Hard Stuff Flashcards
1
Q
What does the mass number tell you?
A
-The total number of protons and neutrons.
2
Q
What does the atomic number tell you?
A
-The number of protons.
3
Q
What is the relative mass of a proton?
A
-1.
4
Q
What is the relative mass of a neutron?
A
-1.
5
Q
What is the relative mass of an electron?
A
-Very small. Nearly 0.
6
Q
What is a compound?
A
- A compound is formed when atoms of two or more elements are chemically combined together. For example, carbon dioxide is a compound formed from a chemical reaction between carbon and oxygen.
- It’s difficult to separate the two original elements out again.
7
Q
What is an isotope?
A
-Isotopes are different atomic forms of the same element, which have the same number of protons but a different number of neutrons.
8
Q
What is a popular pair of isotopes?
A
-Carbon-12 and Carbon-14.
9
Q
What is ionic bonding?
A
-In ionic bonding, atoms lose or gain electrons to form charged particles (called ions) which are then strongly attracted to one another (because of the attraction from
10
Q
What is an ion?
A
-A charged particle.
11
Q
How does ionic bonding happen?
A
- Groups 1&2 (metals), e.g. sodium, potassium, calcium etc. only have 1 or 2 electrons in their outer shell, so therefore they want to get rid of this in order to get a full outer shell as this is desired by electron shells as they try to have the same electronic structure as a noble gas). So therefore, they get rid of the extra electron which leaves as an ion instead.
- Groups 6&7 (non-metals), such as oxygen and chlorine, have 6 or 7 electrons in their outer shells, so their outer shells are nearly full. So therefore, they’re pretty keen to gain that one extra one or two electrons to fill the shell up.
- When they do this, they become ions, and they have latched onto the atom (ion) that previously just gave away the electrons.
12
Q
What is ionic bonding between?
A
-A metal and a non-metal.
13
Q
What type of structures do ionic compounds have?
A
- Ionic compounds always have giant ionic lattices.
- The ions form a closely packed regular lattice arrangement.
- These are very strongly electrostatic forces of attraction between oppositely charged ions, in all directions.
14
Q
What is a example of one giant ionic lattice?
A
-A single crystal of sodium chloride (salt) is one giant ionic lattice, which is why salt crystals tend to be in a cuboid shape. The Na+ and Cl- ions are held together in a regular lattice.
15
Q
In a giant ionic lattice structure, what type of forces hold the atoms together?
A
-Very strong electrostatic forces of attraction between oppositely charged ions, in all directions.
16
Q
What are the similar properties of ionic compounds?
A
- All ionic compounds have similar properties.
- They all have high melting points and high boiling points due to the strong attraction between the ions. It takes a large amount of energy to overcome this attraction.
- When ionic compounds melt, the ions are free to move and they’ll carry electric current.
- They do dissolve easily in water though. The ions separate and are all free to move in the solution, so they’ll carry electric current.
17
Q
What type of ions do Group 1 and 2 metals form?
A
- Group 1 and 2 elements are metals and they lose electrons to form positive ions (losing electrons which are negatively charged).
- For example, Group 1 elements (the alkali metals) form ionic compounds with non-metals where the metal ion has a 1+ charge. E.g. K+Cl-
18
Q
What type of ions do group 6 and 7 elements make?
A
- Group 6 and 7 elements are non-metals. They gain electrons to form negative ions.
- For example, Group 7 elements (the halogens) form ionic compounds with the alkali metals where the halide ion has a 1- charge. E.g. Na+Cl-.
19
Q
How can you tell what the charge on positive ions is?
A
- The charge on positive ions is the same as the group number of the element.
- For example, Positive ions: Group 1: Li+, Na+ and K+. Group 2: Be^2+, Mg^2+ and Ca^2+.
- For negative ions, for example, Group 6: O^2-. For Group 7: F- and Cl-.
20
Q
What elements can form ionic compounds?
A
- Only elements at opposite sides of the periodic table will form ionic compounds, e.g. Na and Cl, where one of them becomes a positive ion and one becomes a negative ion.
- Any of the positive ions in Group 1 and Group 2 can combine with any of the negative ions to form an ionic compound.
21
Q
What do the + and - charges tell us?
A
-The + and - charges we talk about, e.g. Na+ for sodium, just tell you what type of ion the atom will form in a chemical reaction. In sodium metal there are only neutral sodium atoms, Na. The Na+ ions will only appear if the sodium metal reacts with something like water or chlorine.
22
Q
What are ionic compounds made up of?
A
-A positively charged part and a negatively charged part.
23
Q
What is the overall charge of any compound?
A
-The overall charge of any compound is zero.
24
Q
How can you work out the formula for an ionic compound?
A
- You can use the charges on the individual ions present to work out the formula for the ionic compound.
- For example, Sodium chloride contains Na+ (+1) and Cl- (-1) ions. (+1) + (-1) = 0. Charges are balanced with one of each ion, so the formula for sodium chloride = NaCl.
- Another example, Magnesium chloride contains Mg^2+ (+2) and Cl- (-1) ions. Because a chloride ion only has a 1- charge we will need two of them to balance out the 2^+ charge of a magnesium ion. This gives us the formula MgCl2.
25
How do you draw the electronic structure of simple ions?
-Use a big square bracket and a + or - to show the charge.
26
What is covalent bonding?
- Where atoms share electrons with each other so that they've got full outer shells.
- They only share electrons in their outer shells (highest energy levels).
- This way both atoms feel that they have a full outer shell, making them happy as having a full outer shell gives them the electronic structure of a noble gas.
- Each covalent bond provides one extra shared electron for each atom.
- So, a covalent is a shared pair of electrons.
- Each atom involved has to make enough covalent bonds to fill up its outer shell.
27
How does Hydrogen bond with another Hydrogen and Chlorine with Chlorine (they go around in pairs)?
- Covalently.
- Hydrogen atoms have just one electron. They only need one more to complete the first shell.
- Chlorine atoms also need only one more electron.
- So they often form single covalent bonds.
28
What is the symbol to show a covalent bond?
—
29
What is the important thing to remember in a dot and cross diagram?
-In a dot and cross diagram (shows electrons) you only have to draw the outer shell of electrons.
30
What bonds make up methane?
- Covalent bonds.
- Carbon has four outer electrons, which is half a full shell. So it forms four covalent bonds to make up its outer shell.
31
What bonds make up Hydrogen Chloride?
- Covalent bonds.
| - This is very similar to H2 and Cl2. Again, both atoms only need one more electron to complete their outer shells.
32
What bonds make up Ammonia (NH3)?
- Nitrogen has five outer electrons.
| - So it needs to form three covalent bonds to make up the extra three electrons needed.
33
What bonds make up Water (H2O)?
- Oxygen atoms have six outer electrons.
- They sometimes form ionic bonds by taking two electrons to complete their outer shell (Not H2O).
- However they'll also cheerfully form covalent bonds and share two electrons instead.
- In water molecules, the oxygen shares electrons with the two H atoms.
34
What bonds make up Oxygen (O2)?
- In oxygen gas, oxygen shares two electrons with another oxygen to get a full outer shell.
- A double covalent bond is formed.
35
What are simple molecular substances?
- The atoms form very strong covalent bonds to form small molecules of several atoms.
- By contrast, the forces of attraction between these molecules are very weak.
- The result of these feeble intermolecular forces is that the melting points are very low, because the molecules are easily parted from each other. It's the intermolecular forces that get broken when simple molecular substances melt or boil - not the much stronger covalent bonds.
- Most molecular substances are gases or liquids at room temperature, but they can be solids.
- Molecular substances don't conduct electricity - there are no ions so there's no electrical charge.
36
What are giant covalent structures?
- Giant covalent structures are macromolecules.
- These are similar to giant ionic structures (lattices) except that there are no charged ions.
- All the atoms are bonded to each other by strong covalent bonds.
- This means that they have very high melting and boiling points.
- They don't conduct electricity - not even when molten (except for graphite).
- The main examples are diamond and graphite, which are both made only from carbon atoms, and silicon dioxide (silica).
37
How is diamond structured?
- Each carbon atom forms four covalent bonds in a very rigid didn't covalent structure.
- This structure makes diamond the hardest natural substance, so it's used for drill tips.
- And it's pretty and sparkly too.
38
How is Graphite structured?
- Each carbon atom only forms three covalent bonds.
- This creates layers which are free to slide over each other, like a pack of cards - so graphite is soft and slippery.
- The layers are held together so loosely that they can be rubbed off onto paper - that's how a pencil works.
- This is because there are weak intermolecular forces between the layers.
- Graphite is the only non-metal which is a good conductor of heat and electricity.
- Each carbon atom has one delocalised (free) electron and it's these free electrons that conduct heat and electricity.
39
What structures do metals have?
- Metals also consist of a giant structure (giant metallic).
- Metallic bonds involve 'free electrons' which produce all the properties of metals. These delocalised (free) electrons come from the outer shell of every metal atom in the structure.
- These electrons are free to move through the whole structure and so metals are good conductors of heat and electricity.
- These electrons also hold the atoms together in a regular structure. There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons.
- They also allow the layers of atoms to slide over each other, allowing metals to be bent and shaped.
40
What type of forces of attraction are involved in giant metallic?
-Electrostatic attraction forces.
41
What type of forces of attraction are involved in giant metallic and giant ionic structures?
-Electrostatic attraction forces.
42
What type of forces of attraction are involved in simple molecular and giant covalent?
-Intermolecular forces.
43
What physical properties do giant metallic structures have?
- Good conductors of heat and electricity because of delocalised (free) electrons.
- Regular structure due to electrostatic attraction between the positive metal ions and the negative electrons due to the delocalised (free) electrons.
- Layers of atoms can slide over each other, so metals can be bent and shaped due to the delocalised (free) electrons.
44
What are alloys?
- Pure metals often aren't quite right for certain jobs. So scientists mix two or more metals together - creating an alloy with the properties they want.
- Different elements have different sized atoms. So, when another metal is mixed with a pure metal, the new metal atoms will distort the layers of metal atoms, making it more difficult for them to slide over each other. So alloys are harder.
45
What are the physical properties of giant ionic structures?
- High melting points.
- High boiling points.
- Can conduct electricity when molten.
46
What are the physical properties of simple molecular?
- Low melting points.
- Low boiling points.
- Can't conduct electricity.
47
What are the physical properties of giant covalent structures?
- High melting points.
- High boiling points.
- Can't conduct electricity.
48
What are the physical properties of giant metallic structures?
- High melting points.
- High boiling points.
- Can conduct electricity (delocalised electrons).
49
What are smart materials?
-Smart materials behave differently depending on the conditions, e.g. temperature.
50
What is a good example of a smart material?
- A good example is nitinol - a "shape memory alloy". It's a metal alloy (about half nickel, half titanium) but when it's cool you can bend/twist it I've rubber. Bend it too far, though and it stays bent. But, if you heat it above a certain temperature, it goes back to a "remembered" shape.
- It's really handy for glasses frames. If you accident,y bend them, you can just pop them into a bowl of hot water and they'll jump back into shape.
- Nitinol is also used in dental braces. In the mouth it warms and tries to return to a 'remembered' shape, and so it gently pulls the teeth with it.
51
What are nanoparticles?
- Really tiny particles, 1-100 manometers across, are called 'nanoparticles' (1nm = 0.000 000 001m).
- Nanoparticles contain roughly a few hundred atoms.
- Nanoparticles include fullerenes.
- A nanoparticles has very different properties from the 'bulk' chemical that it's made from - e.g. fullerenes have different properties from big lumps of carbon.
52
What are fullerenes?
-These are molecules of carbon, shaped like hollow balls or closed tubes. The carbon atom,s are arranged in hexagonal rings. Different fullerene contain different numbers of carbon atoms.
53
What are nanotubes?
- Fullerenes can be joined together to form nanotubes - teeny tiny hollow carbon tubes a few nanotubes across.
- All those covalent bonds make carbon nanotubes very strong. They can be used to reinforce graphite in tennis rackets.
54
What can nanotubes be used for?
-To reinforce graphite in tennis rackets.
55
What is using nanoparticles known as?
-Using nanoparticles is known as nanoscience.
56
What new uses of nanoparticles are being developed (7 points)?
- They have a huge surface area to volume ratio, so they could help make new industrial catalysts.
- You can use nanoparticles to make sensors to detect one type of molecule and nothing else. These highly specific sensors are already being used to test water purity.
- Nanotubes can be used to make stronger, lighter building materials.
- New cosmetics, e.g. sun tan cream and deodorant, have been made using nanoparticles. The small particles do their job but don't leave white marks on the skin.
- Nanomedicine = hot topic. Idea = tiny fullerenes are absorbed more easily by the body than most particles. This means they could deliver drugs right into the cells where they're needed.
- New lubricant coatings are being developed using fullerenes. These coatings reduce friction a bit like ball bearings and could be used in all sorts of places from artificial joints to gears.
- Nanotubes conduct electricity, so they can be used in tiny electric circuits for computer chips.
57
What are weak forces like in plastics?
-Individual tangled chains of polymers, held together by weak intermolecular forces,mare free to slide over each other.
58
What are strong forces like in plastics?
-Some plastics have stronger intermolecular forces between the polymer chains, called cross links, that hold the chains firmly together.
59
What are thermosoftening polymers?
- They don't have cross-linking between chains. The forces between the chains are really easy to overcome, so it's dead easy to melt the plastic.
- When it cools, the polymer hardens into a new shape.
- You can melt these plastics and remould them as many times as you like.
60
What are thermosetting polymers?
- They have crosslinks.
- These hold the chains together in a solid structure.
- The polymer doesn't soften when it's heated.
- Thermosetting polymers are the tough guys of the plastic world.
- They're strong, hard and rigid.
61
How do you make polymers have different properties?
- How you make a polymer affects it's properties.
| - The starting materials and reaction conditions will affect the properties of a polymer.
62
What are the two types of polyethene that you can make?
-Low-density (LD) and High-density (HD) polyethene.
63
How is Low density (LD) polyethene made and what is it usually used for?
```
Low density (LD) polyethene is made by heating ethene to about 200degress under high pressure.
-It's flexible and is used for bags and bottles.
```
64
How is high density (HD) polyethene made and what is it usually used for?
- High density (HD) polyethene is made at a lower temperature and pressure (with a catalyst).
- It's more rigid and is used for water tanks and drainpipes.
65
What type of plastic would you use for a hot drink?
- Low cost (disposable).
| - High melting point (for hot drinks).
66
What type of plastic would you use for clothing?
- Flexible (essential for clothing).
| - Able to make into fibres (clothing is usually woven).
67
What type of plastic would you use for a measuring cylinder?
-Transparent and resistant to chemicals (you need to be able to see the liquid inside and the liquid and measuring cylinder mustn't react with each other).
68
What is the relative atomic mass?
-Relative atomic mass Ar, is usually just the same as the mass number of the element.
69
What is relative formula mass?
- It is just all the relative atomic masses added together to get the relative formula mass - Mr.
- For example, MgCl2 is just 24 + (35.5 X 2) = 95. S Mr of MgCl2 is simply 95.
70
What is one mole of a substance known as?
-The relative formula mass (Ar or Mr) of a substance in grams is known as one mole of that substance.
71
What is the formula for the number of moles?
-Number of moles = Mass in g (of element or compound) divided by the Mr (of element or compound).
72
What is the formula for finding the percentage mass of an element in a compound?
-Percentage mass of an element in a compound = Ar x No. of atoms (of that element) divided by the Mr (of whole compound) x100.
73
What are the steps to finding the empirical formula of a compound (from masses or percentages)?
- List all the elements in the compound (there's usually only two or three).
- Underneath them, write their experimental masses (ones given to you) or percentages.
- Divide each mass or percentage by the Ar for that particular element.
- Turn the numbers you get into a nice simple ratio by multiplying and/or dividing them by well-chosen numbers.
- Get the ratio in its simplest form, and that tells you the empirical formula of the compound.
74
What are the steps to calculating masses in reactions?
- Write out the balanced equation.
- Work out the Mr of the two bits you want.
- Apply the rule: Divide to get one, then multiply to get all (But you have to apply this first to the substances they give you information about, and then the other one.).
75
What is the yield?
-The amount of product you get is known as the yield.
76
How do you change the amount of yield you get?
-The more reactants you start with, the higher the actual yield will be.
77
What is the percentage yield?
- Percentage yield is given by the formula:
| - Percentage yield = actual yield (grams) divided by predicted yield (grams) x 100.
78
What is percentage yield?
- Percentage yield is always somewhere between 0 and 100%.
- A 100% percentage yield means that you got all the product you expected to get.
- A 0% yield means that no reactants were converted into product, i.e. no product at all was made.
79
Why is a yield always less than 100% and never 100%? (3 points).
-The reaction is reversible. A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants. For examples ammonium chloride = (reversible reaction sign should be there
80
When is it important to think about the product yield?
-Thinking about product yield is important for sustainable development.
81
What is sustainable development?
-Sustainable development is about making sure that we don't use resources faster than they can be replaced - there needs to be enough for future generations too. So, for example, using as little energy as possible to create the highest product yield possible means that resources are saved. A low yield means wasted chemicals - not very sustainable.
82
What are the two ways of identifying and analysing substances?
- Paper chromatography.
| - Gas chromatography.
83
How do you do paper chromatography?
- A food colouring might contain one dye or it might be a mixture of dyes. Here's how you can tell:
- Extract the colour from a food sample by placing it in a small cup with a few drops of solvent (can be water, ethanol, salt water, etc).
- Put spots of the coloured solution on a pencil baseline on filter paper. (Don't use pen because it might dissolve in the solvent and confuse everything).
- Roll up the sheet and put it in a beaker with some solvent - but keep the baseline above the level of the solvent.
- The solvent seeps up the paper, taking the dyes with it. Different dyes form spots in different places.
- Watch out though, a chromatogram with four spots means at least four dyes, not exactly four dyes. There could be five dyes, with two of them making a spot in the same place. It can't be three dyes though, because one dye can't split into two spots.
84
Why must the baseline be drawn in pencil and bot pen in paper chromatography?
-Because pen might dissolve in the solvent and confuse everything, but pencil won't.
85
How many dyes will a chromatogram with four spots have?
- Watch out though, a chromatogram with four spots means at least four dyes, not exactly four dyes.
- There could be five dyes, with two of them making a spot in the same place.
- It can't be three dyes though, because one dye can't split into two spots.
86
What are the advantages to using instrumental methods (using machines) in chromatography?
- Very sensitive - can detect even the tiniest amounts of substances.
- Very fast and tests can be automated.
- Very accurate.
87
How is gas chromatography done?
- Gas chromatography can separate out a mixture of compounds and help you identify the substance present.
- A gas is used to carry substances through a column packed with a solid material.
- The substances travel through the tube at different speeds, so they're separated.
- The time they take to reach the detector is called the retention time. It can be used to help identify the substances.
- The recorder draws a gas chromatograph. The number of peaks show the number of different compounds in the sample.
- The position of the peaks shows the retention time of each substance.
- The gas chromatography column can also be linked to a mass spectrometer. This process is known as GC-MS and can identify the substances leaving the column very accurately.
88
How do you work out the relative molecular mass from gas chromatography?
-You can work out the relative molecular mass of each of the substances from the graph it draws. You just read off from the molecular ion peak (the peak from the relative atomic mass is the relative molecular mass on the gas chromatograph).
89
What is GC-MS?
- Gas Chromatography - Mass Spectrometer.
- The gas chromatography column can also be linked to a mass spectrometer. This process is known as GC-MS and can identify the substances leaving the column very accurately.
90
How do you know how many different compounds there are from a gas chromatograph?
-The recorder draws a gas chromatograph. The number of peaks shows the number of different compounds in the sample.
91
What is the retention time of a substance in gas chromatography?
-The time the substance takes to reach the doctor from being out into the column packed with solid material is called the retention time.
92
What does the position of the peaks show us on a gas chromatograph?
-The position of the peaks shows the retention time of each substance, so allows us to help identify the substances.
93
What is an example of the slowest rates of reactions?
-One of the slowest rates of reactions is the rusting of iron.
94
What is n example of a rate of reaction with a moderate speed?
-A moderate speed reaction is a metal (like magnesium) reacting with acid to produce a gentle stream of bubbles.
95
What is an example of a really fast rate of reaction?
-A really fast reaction is an explosion, where it's all over in a fraction of a second.
96
What four things does the rate of reaction depend on?
- Temperature.
- Concentration (or pressure for gasses).
- Catalyst.
- Surface are of solids (or size of solid pieces).
97
What could an increased rate of reaction be due to?
- Increase in temperature.
- Increase in concentration (or pressure).
- Catalyst added.
- Solid reactant crushed up into small bits (smaller total surface area/size of solid pieces).
98
What does it mean if many lines converge (join together) on the same level at the end on a rate of reaction graph testing a particular reaction under different conditions?
-If many of the lines converge at the same level at the end or at any point on the graph, it shows that they all produce the same amount of product, although they take different times to get there.
99
What is the formula to work out the rate of reaction?
-Rate of reaction = amount of reactant used or amount of product formed divided by time.
100
What are the three different ways the rate of reaction can be measured?
- Precipitation.
- Change in Mass (Usually Gas given off).
- The volume of gas given off.
101
How is precipitation a way to measure the rate of reaction?
- This is when the product of the reaction is a precipitate which clouds the solution.
- Observe a mark (e.g. a cross drawn with a thick, permanent black marker on a piece of paper underneath the conical flask) through a solution and measure how long it takes for it to disappear.
- The quicker the mark disappears, the quicker the reaction.
102
What are the disadvantages to using precipitation as a way to measure the rate of reaction?
- This only works for reactions whee the initial solution is rather see-through.
- The result is very subjective - different people might not agree over the exact point when the mark 'disappears'.
103
How is change in mass (usually gas given off) a way to measure the rate of reaction?
- Measuring the speed of a reaction that produces a gas can be carried out on a mass balance.
- As the gas is released the mass disappearing is easily measured on the balance.
- The quicker the reading on the balance drops, the faster the reaction.
104
What are the advantages to using change in mass (usually gas given off) as a way to measure the rate of reaction?
- Rate of reaction graphs are particularly easy to plot using the results from this method.
- This is the most accurate of the three methods (precipitation, change in mass (usually gas given off), or the volume of has given off) because the mass balance is very accurate (small degree of accuracy, it's not hard to read and it picks up the slightest change/very sensitive to mass change).
105
What are the disadvantages to using change in mass (usually gas given off) as a way to measure the rate of reaction?
- It has the disadvantage of releasing the gas straight into the room.
- But other than that, it is pretty good and is the best out of the three (Precipitation, change in mass (usually gas given off).
106
How is the volume of gas given off a way to measure the rate of reaction?
- This involves using a gas syringe to measure the volume of gas given off.
- The more gas given off during a given time interval, the faster the reaction.
107
What are the advantages to using the volume of gas given off as a way to measure the rate of reaction?
- A graph of gas volume against time elapsed could be plotted to give a rate of reaction graph.
- Gas syringes usually give volumes accurate to the nearest millilitre, so they're quite accurate.
108
What is the disadvantage to using the volume of gas given off as a way to measure the rate of reaction?
-You have to be quite careful though - if the reaction is too vigorous, you can easily blow the plunger out of the end of the syringe (as there will be too much gas for the spring to hold, so it will push the syringe so far, that it will end up going out of the end of syringe and you can't do anything to stop it).
109
What is the reaction of hydrochloric acid and marble chips used to demonstrate (which factor on the rate of reaction)?
-This experiment is often used to demonstrate the effect of breaking the solid up into small bits (smaller surface area).
110
What is the reaction of hydrochloric acid and marble chips method?
- Measure the volume of gas evolved with a gas syringe and take readings at regular intervals.
- Make a table of readings and plot them as a graph. You choose regular time intervals, and time goes on the x-axis and volume goes on the y-axis.
- Repeat the experiment with exactly the same volume of acid, and exactly the same mass of marble chips, but with the marble more crunched up.
- Then repeat with the same mass of powdered chalk instead of marble chips.
111
What does the reaction of hydrochloric acid and marble chips show?
- Using finer particles means that the marble has a larger surface area.
- A larger surface causes more frequent collisions so the rate of reaction is faster.
- If a greater mass of small marble chips is added, then the extra surface gives a quicker reaction and there is also more gas evolved overall.
112
What is the reaction of magnesium metal with dilute HCl used to demonstrate (which factor on the rate of reaction)?
-This reaction is good for measuring the effects of increased concentration (as in the marble/acid reaction).
113
What is the reaction of magnesium metal with dilute HCl method?
- This reaction gives off hydrogen gas, which we can measure with a mass balance, as shown.
- In this experiment, time also goes on the x-axis and volume goes on the y-axis.
- Take readings of mass at regular time intervals.
- Put the results in a table and work out the loss in mass for each reading. Plot a graph.
- Repeat with more concentrated acid solutions, but always with the same amount of magnesium.
- The volume of acid must always be kept the same too - only the concentration is increased.
114
How is the reaction of hydrochloric acid and marble chips different to the reaction of magnesium metal with dilute HCl?
-It is different to the reaction of hydrochloric acid and marble chips as that uses a gas syringe to measure gas lost whereas the reaction of magnesium metal with dilute HCl uses a mass balance to measure gas lost.
115
What does the reaction of magnesium metal with dilute HCl show?
-The graphs show the same old pattern - a higher concentration gives a steeper graph, with the reaction finishing much quicker.
116
What can the reaction of sodium thiosulfate and HCl producing a cloudy precipitate demonstrate (which factor on the rate of reaction)?
-The reaction can be repeated for solutions at different temperatures. In practice, that's quite hard to do accurately and safely (it's not a good idea to heat an acid directly). The best way to do it is to use a water bath to heat both solutions to get the right temperature before you mix them.
117
What is the reaction of sodium thiosulfate and HCl producing a cloudy precipitate method?
- These two chemicals are both clear solutions.
- They react together to form a yellow precipitate of sulfur.
- The experiment involves watching a black mark disappear through the cloudy sulfur and timing how long it takes to go.
- The depth of liquid must be kept the same each time, of course.
118
What does the reaction of sodium thiosulfate and HCl producing a cloudy precipitate show?
-The results will of course show that the higher the temperature the quicker the reaction and therefore the less time it takes for the mark to disappear.
119
What else can the reaction of sodium thiosulfate and HCl producing a cloudy precipitate be used to demonstrate (which factor on the rate of reaction)?
-This reaction can also be used to test the effects of concentration.
120
What is one disadvantage of the reaction of sodium thiosulfate and HCl producing a cloudy precipitate?
- This reactions doesn't give a set of graphs.
| - All you get is a set of readings of how long it took till the mark disappeared for each temperature.
121
What is the decomposition of hydrogen peroxide used to demonstrate (which factor on the rate of reaction)?
-This is a good reaction for showing the effect of different catalysts.
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What is the decomposition of hydrogen peroxide method?
- The decomposition of hydrogen peroxide is: 2(H2O2) > 2(H2O) + O2.
- This is normally quite slow, but a sprinkle of manganese (IV) oxide catalyst speeds it up no end. Other catalysts which work are found in: a) potato peel and b) blood.
- Oxygen gas is given off, which provides an ideal way to measure the rate of reaction using the gas syringe method.
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What does the decomposition of hydrogen peroxide show?
- Same old graphs.
- Better catalysts give a quicker reaction, which is shown by a steeper graph which levels off quickly.
- This reaction can also be used to measure the effects of temperature, or of concentration of the H2O2 solution. The graphs will look just the same.
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What is the collision theory?
-It says that the rate of reaction simply depends on how often and how hard the reacting particles collide with each other. The basic idea is that particles have to collide in order to react, and they have to collide hard enough (with enough energy).
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What three factors increase the nu,her of collisions?
- Higher temperature increases collisions.
- Higher concentration (or PRESSURE) increases collisions.
- Larger surface area increases collisions.
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How does a higher temperature increase collisions?
- When the temperature is increased the particles all move quicker (as they have more energy as heat).
- If they're moving quicker, they're going to collide more often.
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How does a higher concentration (or PRESSURE) increase collisions?
- If the solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules which makes collisions between the important particles more likely.
- In a gas, increasing the pressure means the particles are more squashed up together so there will be more frequent collisions.
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How does a larger surface area increase collisions?
- If one of the reactants is a solid then breaking it up into smaller pieces will increase the total surface area.
- This means the particles around it in the solution will have more area to work on, so there'll be more frequent collisions.
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Was does a higher temperature also do?
- Higher temperature also increases the energy of collisions, because it makes all the particles move faster.
- Increasing the temperature causes faster collisions.
- Reactions only happen if the particles collide with enough energy.
- The minimum amount of energy needed by the particles to react is known as the activation energy.
- At a higher temperature there will be a more particles colliding with enough energy to make the reaction happen.
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How does a catalyst speed up reactions (speed up the rate of reaction)?
- Many reactions can be speeded up by adding a catalyst.
- A solid catalyst works by giving the reacting particles a surface to stick to. This increases the number of successful collisions (and so speeds the reaction up).
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What is the activation energy?
-The minimum amount of energy needed by the particles to react is known as the activation energy.
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What is the definition for a catalyst?
-A catalyst is a substance which speeds up a reaction, without being change or used up in the reaction.
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Why are catalysts used in industrial reactions?
-Catalysts help reduce costs in industrial reactions.
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How do catalysts help reduce costs in industrial reactions?
- Catalysts are very important for commercial reasons - most industrial reactions use them.
- Catalysts increase the rate of the reaction, which saves a lot of money simply because the plant doesn't need yo operate for as long to produce the same amount of stuff.
- Alternatively, a catalyst will allow the reaction to work at a much lower temperature. That reduces the energy used up in a reaction (the energy cost), which is good for sustainable development and can save a lot of money too.
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What are the disadvantages to using catalysts in industrial reactions?
- They can be very expensive to buy, and often need to be removed from the product and cleaned. They never get used up in the reaction though, so once you've got them you can use them over and over again.
- Different reactions use different catalysts, so if you make more than one product at your plant, you'll probably need to buy different catalysts for the,
- Catalysts can be 'poisoned' by impurities, so they stop working, e.g. sulfur impurities can poison the iron catalyst used in the Haber process (used to make ammonia for fertilisers). That means you have to keep your reaction mixture very clean.
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What is an exothermic reaction?
-An exothermic reaction is one which transfers energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature.
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What is the best example of an exothermic reaction?
- The best example of an exothermic reaction is burning fuels - also called combustion.
- This gives out a lot of heat - it's very exothermic.
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What are other examples of an exothermic reaction?
-Neutralisation reactions (acid+alkali) are also exothermic.
-Many oxidation reactions are exothermic. For example, adding sodium to water produces heat, so it must be exothermic. The sodium emits heat and moves about on the surface of the water as it is oxidised.
-
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What are some everyday uses of exothermic reactions?
- Exothermic reactions have lots of everyday uses. For example, some hand warmers use the exothermic oxidation of iron in air (with a salt solution catalyst) to generate heat.
- Self heating cans of hot chocolate and coffee also rely on exothermic reactions between chemicals in their bases.
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What are endothermic reactions?
-An endothermic reaction is one which takes in energy from the surroundings, usually in the form of heat and is usually shown by a fall in temperature.
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What are a good example of an endothermic reaction?
- Endothermic reactions are much less common.
- Thermal decompositions are a good example: Heat must be supplied to make calcium carbonate decompose to make quicklime.
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What are some everyday uses of endothermic reactions?
-Endothermic reactions also have everyday uses. For example, some sports injury packs use endothermic reactions - they take in heat and the pack becomes very cold. More convenient than carrying ice around.
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What type of reactions can reversible reactions be?
- In reversible reactions, if the reaction is endothermic in one direction, it will be exothermic in the other direction.
- The energy absorbed by the endothermic reaction is equal to the energy released during the exothermic reaction.
- A good example is the thermal decomposition of hydrated copper sulfate. Hydrated > (endothermic) anhydrous copper sulfate + water
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What is the pH scale?
- The oH scale is a measure of how acidic or alkaline a solution is.
- The strongest acid has a pH 0.
- The strongest alkali has pH 14.
- A neutral substance has pH 7 (e.g. pure water).
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What is an indicator?
- An indicator is a dye that changes colour.
- The dye in the indicator changes colour depending on whether it's above or below a certain pH.
- Universal indicator is a combination which gives the colour shown above.
- Ir's very useful for estimating the pH of a solution.
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What is an acid?
- An acid is a substance with a pH of less than 7.
| - Acids form H+ ions in water.
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What is a base?
-A base is a substance with a pH of greater than 7.
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What is an alkali?
- An alkali is a base that dissolves in water.
| - Alkalis form OH- ions in water.
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What type of ions make a solution acidic?
-H+ ions make a solution acidic.
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What type of ions make a solution alkaline?
-OH- ions make a solution alkaline.
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What is the reaction between acids and bases?
- The reaction between acids and bases is called neutralisation.
- acid+ base > salt + water.
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What is the equation for neutralisation in terms of H+ (aq) and OH- (aq) ions?
-H+ (aq) + OH- (aq) > H2O (l).
153
What do hydrogen (H+) ions react with hydroxide (OH-) ions to produce?
-Hydrogen (H+) ions react with hydroxide (OH-) ions to produce water.
154
What is the state symbol for a solid?
-(s) - solid.
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What is the state symbol for a liquid?
-(l) - liquid.
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What is the state symbol for a gas?
-(g) - gas.
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What is the state symbol for Ann aqueous solution (dissolved in water)?
-(aq) - Dissolved in water (aqueous).
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What does an acid + metal react to produce?
- Acid + Metal > Salt + Hydrogen.
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What things do you need to remember with the metal reacting with acids to make salts and hydrogen experiment?
- The more reactive the metal, the faster the reaction will go - very reactive metals (e.g. sodium) react explosively.
- Copper does not react with dilute acids at all - because it's less reactive than hydrogen.
- The speed of reaction is indicated by the rate at which the bubbles of hydrogen are given off.
- The hydrogen is confirmed by the burning of a splint test giving the notorious 'squeaky pop'.
- The name of the salt produced depends on which metal is used, and which acid is used.
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What is a test for hydrogen?
-Hydrogen is confirmed by the burning splint test giving the notorious 'squeaky pop'.
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What type of salts will hydrochloric acid make?
- Hydrochloric acid will always produce chloride salts.
- 2HCl + Mg > MgCl2 + H2 (Magnesium chloride).
- 6HCl + 2Al > 2AlCl3 + 3H2.
- 2HCl + Zn > ZnCl2 + H2.
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What type of salts will sulfur is acid always react to produce?
- Sulfuric acid will always produce sulfate salts.
- H2SO4 + Mg > MgSO4 + H2 (Magnesium sulfate).
- 3H2SO4 + 2Al > 2Al2(SO4)3 + 3H2 (Aluminium sulfate).
- H2SO4 + Zn > ZnSO4 + H2 (Zinc Sulfate).
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What type of salts will nitric acid react to produce when neutralised?
-Nitric acid produces nitrate salts when neutralised, but with metals and produce nitrogen oxides instead.
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What do all metal oxides and metal hydroxides react with acids to form?
- All metal oxides and metal hydroxides react with acids to form a salt and water.
- Acid + Metal Oxide > Salt + Water.
- Acid + Metal Hydroxide > Salt + Water.
- These are both neutralisation reactions.
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What decides the salt?
- The combination of metal and acid decides the salt.
- For example:
- hydrochloric acid + copper oxide > copper chloride + water.
- hydrochloric acid + sodium hydroxide > sodium chloride + water.
- sulfuric acid + zinc oxide > zinc sulfate + water.
- sulfuric acid + calcium hydroxide > calcium sulfate + water.
- nitric acid + magnesium oxide > magnesium nitrate + water.
- nitric acid + potassium hydroxide > potassium nitrate + water.
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What are the symbol equations for the combination of metal and acids making a salt and water?
- The symbol equations are all pretty much the same. Here are two of them:
- H2SO4 (aq) + ZnO (s) > ZnSO4 (aq) + H2O (l).
- HNO3 (aq) + KOH (aq) > KNO4 (aq) + H2O (l).
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What is ammonia neutralised with?
-Ammonia can be neutralised with HN03 to make fertiliser.
-Ammonia dissolves in water to make an alkaline solution.
-When it reacts with nitric acid, you get a neutral salt - ammonium nitrate:
NH3 (aq) + HNO3 (aq) > NH4NO3 (aq).
Ammonia + nitric acid > Ammonium nitrate - just the ammonium salt.
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Why is ammonium nitrate made from ammonia being neutralised with HNO3 to make fertiliser, an especially good fertiliser?
-Ammonium nitrate is an especially good fertiliser because it has nitrogen from two sources, the ammonia and the nitric acid. Kind of double dose. Plants need nitrogen to make proteins.
169
What salts are soluble in water?
- Chlorides.
- Sulfates.
- And nitrates.
170
What salts are insoluble in water?
- Most oxides.
| - And hydroxides.
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How do you make a soluble salt using a metal or an insoluble base?
- You need to pick the right acid, plus a metal or an insoluble base (a metal oxide or ,teal hydroxide). E.g. if you want to make copper chloride, mix hydrochloric acid and copper oxides. E.g. CuO (s) + 2HCl (aq) > CuCl2 (aq) + H2O (l).
- You add the metal, metal oxide or hydroxide to the acid - the solid will dissolve in the acid as it reacts. You will know when all the acid has been neutralised because the excess solid will just drink to the bottom of the flask.
- Then filter out the excess metal, metal oxide or metal hydroxide to get the salt solution. To get pure, solid crystals of the salt, evaporate some of the water (to make the solution more concentrated) and then leave the rest to evaporate very slowly. This is called crystallisation.
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How do you make a soluble salt with an alkali?
- You can't use the crystallisation method with alkalis (soluble bases) like sodium, potassium or ammonium hydroxides because you can't tell whether the reaction has finished - you can't just add an excess to the acid and filter out what's left.
- You have to add exactly the right amount of alkali to just neutralise the acid - you need to use an indicator to show when the reaction's finished. Then repeat using exactly the same volumes of alkali and acid so the salt isn't contaminated with indicator.
- Then just evaporate off the water to crystallise the salt as normal.
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How do you make an insoluble salt using precipitation reactions?
-If the salt you what to make is insoluble me you can use a precipitation reaction.
-You just need to pick two solutions that contain the ions you need. E.g. to make lead chloride you need a solution which contains lead ions and one which contains. So you can mix lead nitrate solution (most nitrates are soluble) with sodium chloride solution (all group 1 compounds are soluble). E.g. Pb(NO3)2 (aq) + 2NaCl (aq) > PbC
2 (s) + 2NaNO3 (aq).
-Once the salt has precipitated out (and is lying at the bottom of your flask), all you have to do is filter it from the solution, wash it and then dry it on filter paper.
-Just mix two solutions contains the ions you need - simple as that.
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What can precipitation reactions be used for?
- Precipitation reactions can be used to remove poisonous ions (e.g. lead) from drinking water.
- Calcium and magnesium ions can also be removed from water this way - they make water "hard", which stops soap lathering properly.
- Another use of precipitation is treating effluent (sewage) - again, unwanted ions can be removed.
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What does electrolysis mean?
-Electrolysis means "splitting up with electricity".
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What is electrolysis?
- Electrolysis means "splitting up with electricity".
- If you pass an electric current through an ionic substance that's molten or in solution, it breaks down into the elements it's made of. This is called electrolysis.
- It requires a liquid to conduct the electricity, called the electrolyte.
- Electrolytes contain free ions - they're usually the molten or dissolved ionic substance.
- In either case it's the free ions which conduct the electricity and allow the whole thing to work.
- For an electrical circuit to be complete, there's got to be a flow of electrons. Electrons are taken away from ions at the positive electrode (anode) and given to other ions at the negative electrode (cathode). As ions gain or lose electrons they become atoms or molecules and are released (in solid form).
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What two things does electrolysis always involve?
- Oxidation.
| - Reduction.
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What is oxidation?
-Oxidation is loss of electrons (or gain of oxygen in core science).
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What is reduction?
-Reduction is gain of electrons (or loss of oxygen in core chemistry).
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What is the acronym to remember what oxidation and reduction and what do the letters stand for?
- OILRIG.
| - Oxidation is loss. Reduction is gain.
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When will a salt conduct electricity?
-When a salt (e.g. lead bromide) is molten it will conduct electricity.
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What happens at the negative electrode (cathode) in electrolysis?
-At the -ve electrode, an ion accepts electron(s) to become one atom.
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What happens at the positive electrode (anode)?
-At the +ve electrode, ions lose electron(s) and become molecules.
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What happens at the positive electrode in the electrolysis of molten lead bromide?
+ve ions are attracted to the -ve electrode.
- Here they gain electrons (reduction).
- Lead is produced at the -ve electrode.
- At the -ve electrode, one lead ion accepts two electrons to become one lead atom.
185
What happens at the positive electrode (anode) in the electrolysis of molten lead bromide?
- ve ions are attracted to the +ve electrode.
- Here they lose electrons (oxidation).
- Bromine is produced at the +ve electrode.
- At the +ve electrode, two bromide ions lose one electron each and become one bromine molecule.
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How does reactivity affect the products formed by electrolysis?
- Sometimes there are more than two free ions in the electrolyte. For example, if a salt is dissolved in water there will also be some H+ and OH- ions.
- At the negative electrode (cathode), if metal ions and H+ ions are present, the metal ions will stay in solution if the metal is more reactive than hydrogen.
- At the positive electrode, if OH- and halide ions (Cl-, Br-, I-) are present then molecules of chlorine, bromine or iodine will be formed.
- If no halide is present, then oxygen will be formed.
187
Why do metals stay in a solution in electrolysis if the metal is more reactive then hydrogen?
- This is because, the more reactive an element, the keener it is to stay as ions.
- So, hydrogen will be produced unless the metal is less reactive than it.
188
What are the three useful products made from the electrolysis of sodium chloride solution?
- Sodium hydroxide.
- Hydrogen.
- Chlorine.
189
What happens at the positive electrode in the electrolysis of sodium chloride solution?
- At the positive electrode, two chloride (Cl-) ions lose their electrons and become one chlorine molecule.
- ve ions are attracted to the +ve electrode.
- Here they lose electrons (oxidation).
- Chlorine is produced at the +ve electrode.
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What happens at the negative electrode in the electrolysis of sodium chloride solution?
-At the negative electrode (cathode), two hydrogen ions accept two electrons to become one hydrogen molecule.
-Hydrogen is produced at the -ve electrode.
+ve ions are attracted to the -ve electrode.
-Here they gain electrons (reduction).
191
What happens to the sodium ions in the electrolysis of sodium chloride solution?
- The sodium ions stay in solution because they're more reactive than hydrogen.
- Hydroxide ions from water are also left behind.
- This means that sodium hydroxide (NaOH) is left in the solution.
192
What is the main thing to remember in the half equations for electrolysis?.
-The main thing is to make sure the number of electrons is the same for both half-equations.
193
What are the half-equations for the electrolysis of sodium chloride?
-For the electrolysis of sodium chloride the half-equations are:
Negative electrode: 2H+ + 2e- > H2.
Positive electrode: 2Cl- > Cl2 + 2e- or 2Cl- - 2e- > Cl2.
194
What are the half equations for the electrolysis of molten lead bromide?
-For the electrolysis of molten lead bromide the half equations would be:
Positive electrode: Pb2+ + 2e- > Pb.
Negative electrode: 2Br- > Br2 + 2e- or 2Br- - 2e- > Br2.
195
What useful products from the electrolysis of sodium chloride solution are useful in industry?
- The products of the electrolysis of sodium chloride solution are pretty useful in industry.
- Chlorine has many uses, e.g. in the production of bleach and plastics.
- Sodium hydroxide is a very strong alkali and is used widely in the chemical industry, e.g. to make soap.
196
What is a use of electrolysis?
- Electrolysis is used to remove aluminium from its ore.
- Aluminium is a very abundant (rare) metal, but it is always found naturally in compounds.
- It's main ore is bauxite, and after mining and purifying, a white powder is left.
- This is pure aluminium oxide, Al2O3.
- The aluminium has to be extracted from this using electrolysis.
197
What is added to electrolysis of aluminium oxide to help lower temperature and costs?
- Cryolite is used to lower the temperature (and costs).
- Al2O3 has a very high melting point of over 2000 degrees - so melting it would be very expensive (high melting points = lot of energy required to melt it = very expensive/lot of money needed to fund the lot of energy used to heat up to high melting points).
- Instead the aluminium oxide is dissolved in molten cryolite (a less common ore of aluminium).
- This brings the temperature down to about 900 degrees which makes it cheaper and easier.
- The electrodes are made of carbon (graphite) a good conductor of electricity.
- Aluminium forms at the negative electrode (cathode) and oxygen forms at the positive electrode (anode).
- Negative electrode: Al3+ +3e- > Al. Positive electrode: 2O2- > O2 + 4e-
- The oxygen reacts with the carbon in the electrode (made of graphite which is carbon) to produce carbon dioxide. This means that the positive electrodes gradually get 'eaten away' and have to be replaced every now and then.
198
What is an example of a process which involves electrolysis?
-Electroplating uses electrolysis.
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What is electroplating?
- Electroplating uses electrolysis to coat the surface of one metal with another metal, e.g. you might want to electroplate silver onto a brass cup to make it look nice.
- The negative electrode is the metal object you want to plate HD the positive electrodee is the pure metal you want it to be played with. You also need the electrolyte to contain ions of the plating metal. (The ions that plate the metal object come from the soolution, while the positive electrode keeps the solution 'topped up'.).
- Example: To electroplate silver onto a brass cup, you'd make the brass cup the negative electrode (to attract the positive silver ions), a lump of pure silver the positive electrode and dip them in a solution of silver ions, e.g. silver nitrate.
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What are the different uses for electroplating?
- There are lots of different uses for electroplating:
- Decoration: Silver is attractive, but very expensive. It's much cheaper to plate a boring brass cup with silver, than it is to make the cup out of solid silver - but it looks just as pretty.
- Conduction: Metals like copper conduct electricity well - because of this they're often used to plate metals like electronic circuits and computers.
