Chemistry Unit 2 Flashcards
What is the reaction for neutralisation?
Acid + base –> salt + water
What are the 2 main uses of precipitation reactions?
To remove poisonous ions from drinking water
Treating sewage
For the acid + metal reaction, what indicates the rate of reaction and what confirms the hydrogen?
Rate of reaction = rate at which bubbles of hydrogen are given off
Hydrogen confirmed by the burning splint test giving a squeaky pop
Describe how you would make insoluble salts
Use precipitation
Work out the positive and negative ion of the salt
Mix a nitrate of positive ion in solution with sodium and the negative ion in solution (this is because most nitrates and group 1 compounds are soluble)
You would then get a precipitate of the wanted salt (solid) and sodium nitrate solution in the flask
Then you filter the salt from the solution, wash it and dry it on filter paper
Describe how you make a soluble salt using an alkali
You can’t add an excess of alkali because you can’t tell whether the reaction has finished in this case
You add just the right amount of alkali to acid and order to neutralise the acid (you use an indicator to work out how much alkali is needed to neutralise the acid)
You repeat using exactly the same amounts of acid and alkali so that the salt isn’t contaminated by the indicator
Crystallise the salt
What is ammonium nitrate used for and why?
Very good fertiliser
It has nitrogen from 2 sources (ammonia and nitric acid) and plants need nitrogen to make proteins
Describe how you make a soluble salt using a metal or insoluble base
Pick the correct acid and metal / insoluble base to make the salt you need
Add the insoluble base or metal to the acid and the solid will dissolve in the acid as it reacts
When all acid has been neutralised, the excess solid won’t dissolve
Then filter out the excess solid to get the salt solution
To get pure, solid crystals of the salt, use crystallisation
What is an acid?
A substance with a pH below 7 that forms H+ ions in water
What is an alkali?
A base that dissolves in water (forms OH- ions in water)
Describe crystallisation
To get pure, solid crystals of the salt you use crystallisation
You evaporate some of the water to make the solution more concentrated and then leave the rest to evaporate very slowly
What are the 2 neutralisation reactions and the other similar reaction?
Acid + metal oxide –> salt + water
Acid + metal hydroxide –> salt + water
Similar reaction:
Acid + metal –> salt + hydrogen
What are the 2 ways of making soluble salts?
Using metal or insoluble base
Using an alkali
What salts do hydrochloric, sulphuric and nitric acids produce?
Hydrochloric –> chloride
Sulphuric –> sulphate
Nitric –> nitrate
What is a base?
A substance with a pH above 7
What happens when ammonia reacts with an acid?
Ammonia + hydrochloric acid –> ammonium chloride
Ammonia + sulphuric acid –> ammonium sulphate
Ammonia + nitric acid –> ammonium nitrate
What does diatomic mean?
An element that naturally has 2 covalently bonded atoms such as H^2
Describe electroplating
You can coat the surface of one metal with another metal
The negative electrode is the metal to be plated and the positive electrode is the metal that will plate it. The electrolyte also contains the ions if the playing metal
The ions that plate the metal come from the solution and the positive electrode keeps the solution topped up
Which substances made by electrolysis are diatomic?
Hydrogen at the cathode
Halides at the anode
Show how sodium chloride solution would break down in electrolysis
Hydrogen is less reactive so at the negative electrode, the H+ ions lose their charge
Because a halogen will form at the positive electrode if possible, the Cl- ions will lose their charge and become the halogen chlorine
When the electricity is turned off, the Na+ and OH- ions are left so they react to form sodium hydroxide
What are the 2 reasons for electroplating?
Decoration (plate a cheap metal with an expensive metal to make it look expensive)
Conduction (copper often plates metals for electronic circuits because it conducts electricity so well)
Why does the positive electrode have to be replaced?
When oxygen forms at the electrode, it reacts with the carbon of the electrode and forms carbon dioxide
This reaction eats away the carbon of the electrode
What are the 4 uses of electrolysis?
Extract a metal from an ore
Purify copper
Create substances from salt
Improve surface of a metal
What are the cathode and anode?
Anode is positive electrode
Cathode is negative electrode
What is brine?
Sodium chloride solution
How do you remember the difference between oxidation and reduction?
OIL RIG
Oxidation is loss (of electrons)
Reduction is gain (of electrons)
Why is electrolysis more complicated in aqueous solutions?
Because ions in the water are present as well as the ions in the compound
What is electrolysis?
The breakdown of a substance by passing electricity through it
Why isn’t an ionic solid an electrolyte?
The ions are not free to move so the current cannot pass through them
What are the rules about reactions at the positive electrode?
If hydroxide and halide ions are present, halogens will be produced and the hydroxide will stay as ions
If no halide is present, oxygen will be formed
Why is electrolysis of aluminium oxide so expensive and what is done to counter this?
It has to be heated up to 2000C for it to become molten
Cryolite (less common aluminium ore) is added and this brings the melting point down to 900C
What will form at the positive electrode if possible?
A halogen
What is an electrolyte?
An ionic substance that is either a liquid or dissolved in water
What are the rules about reactions at the negative electrode?
If metal ions and hydrogen ions are present, the metal ions will stay in solution and hydrogen will form if the metal is more reactive than hydrogen
This is because, the more reactive an element, the keener it is to stay as ions
What is a half equation?
A chemical equation that shows how an ion gains or loses electrons at an electrode
2H+ + 2e- –> H^2
2Cl- –> Cl^2 + 2e-
How do OH- ions oxidise? (Chemical equation)
4OH- –> O^2 + 2H^2O + 4e-
What 2 chemical properties are needed to use electrolysis in breaking down of a substance?
Substance is ionic
Ions are free to move
Why is electrolysis avoided if possible?
Expensive due to the cost of the electricity as a high current is needed
Why is electrolysis used for purifying copper?
Copper needs to be very pure for use as electrical wiring
What is Faraday’s law of electrolysis?
The higher the current used, the faster the substance is produced
What are the 2 reasons that the electrolysis of sodium chloride solution is useful in industry?
Chlorine is useful in bleach and plastics
Sodium hydroxide is a very strong alkali and used widely in the chemical industry
What is dynamic equilibrium?
When 2 conflicting sources make a reversible reaction not lose or gain any more products
What is an endothermic reaction?
A chemical reaction that absorbs heat from the surroundings
What is the industrial problem with reversible reactions?
If the reactants and products can’t escape the reaction area, the reaction would reach a state of equilibrium and the products would turn into the reactants just as much as the other way round
Is exothermic or endothermic rarer?
Endothermic reactions are rarer
What is a reversible reaction?
A reaction where the end products can react back into the original reactants
What is the main endothermic reaction?
When calcium carbonate thermally decomposes to form calcium oxide and carbon dioxide
Give 3 ways in which exothermic reactions are used
Heating
Generating electricity
Self-heating cans
What relates exothermic / endothermic and reversible reactions?
The forward reaction would be exothermic / endothermic and the backward reaction would be the opposite
Give 2 ways in which endothermic reactions are used
Ice packs for injuries
Self-cooling cans for drinks
What are the 3 main exothermic reactions?
Burning fuels
Neutralisation reactions
Oxidation reactions
How do we show a reaction is reversible in a chemical formula?
Double-headed arrow
What is an exothermic reaction?
A chemical reaction that transfers heat to the surroundings
Describe the experiment you use to see the effect of a catalyst on rate of reaction
You put hydrogen peroxide in a conical flask and put in a catalyst
Use the volume of gas given off (oxygen gas) to calculate the rate of reaction
Do this method for all the different catalysts to be tested
How do you measure rate of reaction using change in mass?
If a reaction produces a gas, you can measure the rate of reaction by looking at the change in mass (gas is lost)
You measure the change in mass by using a balance and looking at how fast the mass goes down
What are the 2 advantages of using catalysts in industrial reactions?
Increases rate of reaction so the plant doesn’t need to operate for as long saving money
Allows the reaction to work at lower temperatures and pressures
What is the biggest problem with catalysts?
They are very specific
Only one type of catalyst will catalyse a specific reaction
Describe the experiment you use to see the effect of temperature on rate of reaction
Let the 2 clear solutions of sodium thiosulphate and hydrochloric acid react in a comical flask and use the precipitation method to calculate the rate of reaction
Then use a water bath to heat the solutions up before mixing them and calculate the rate of reaction
The second reaction should be faster
How does surface area affect the rate of reaction?
If the surface area is larger, more of the reactant is exposed meaning the particles of the other reactant are more likely to collide with it
How do you measure the rate of reaction with the volume of gas given off?
You use a gas syringe to collect up the gas of the reaction
The more gas given off in a given time, the faster the reaction
Why is a catalytic converter needed?
The harmful gases of carbon monoxide and nitrogen oxides are changed to the much less harmful carbon dioxide and nitrogen
What are the 2 problems with the precipitation rate of reaction experiment?
Different people might not agree on the exact point that the mark disappears
Only works for reactions where the initial solution is clear
What is collision theory?
The theory that substances react when the particles of the reactants collide, break apart and then re-form to create new substances
Describe the experiment you use to see the effect of surface area on rate of reaction
You put marble chips and hydrochloric acid in conical flask and use the volume of gas given off method to calculate the rate of reaction
You then do the same but crunch up the chips more which gives a larger surface area
The second reaction should happen faster
How does concentration change the rate of reaction?
If the particles are more crowded (higher concentration) they are much more likely to collide so the reaction is faster
What are successful collisions?
Collisions that result in a chemical reaction
Describe the experiment you use to see the effect of concentration on rate of reaction
You use the change in mass method to calculate the rate of reaction of magnesium metal and dilute hydrochloric acid
You do the sane reaction with a higher concentration hydrochloric acid
The second reaction should have a higher rate
How do catalysts work?
The catalyst particles collide with the reactant particles and lower the activation energy by providing an alternative route for the reaction
What are the 4 factors that can change the speed of a reaction?
Temperature, concentration, surface area and pressure
Where are catalysts used?
They are used in industrial chemical reactions where there isn’t much time
They are used in catalytic converters
What is the Haber process?
Iron is used as a catalyst to produce ammonia from nitrogen gas and hydrogen gas
What is activation energy?
The amount of energy that needs to be put in to trigger the reaction
What is concentration?
It is the amount of molecules of the reactant dissolved in a given volume of water
How does temperature affect the rate of reaction?
If there is a higher temperature, the particles will vibrate more giving them more energy
More energy means they move faster and are more likely to collide
Give 2 ways in which we can measure the rate of a reaction
How fast the reactants are used up
How fast the products of the reaction are formed
How do you measure rate of reaction with precipitation?
This is when the product of the reaction is a precipitate that clouds the solution
Observe a mark through the solution and measure how long it takes to disappear
The quicker the mark, the quicker the tst
What is the advantage and disadvantage of the change in mass experiment?
Very accurate because the mass balance is accurate
But the gas is released straight into the room
What is pressure?
How much gas has been squashed into a given area
They have more pressure making the particles closer together
What is a catalyst?
A substance that massively increases the rate of a reaction without being used up or changed
What are the 3 ways of measuring the rate of reaction?
Change in mass
Volume of gas given off
Precipitation
What are the 3 disadvantages of using catalysts in industrial reactions?
They often need to be removed from the product and cleaned
Different reactions use different catalysts so they can be quite expensive
Catalysts can stop working because of impurities so you need to keep your reaction mixture very clean
What is the advantage and disadvantage of the volume of gas given off experiment?
The volume of gas measured is very accurate
If the reaction is too violent, you can blow the plunger out of the end of the syringe
How does pressure affect the rate of reaction?
If we squash more gas into a smaller area, the molecules will be closer together meaning they are more likely to collide
What is thin layer chromatography?
A variant of paper chromatography that uses silica plates instead of filter paper as a stationary phase
What do substances need to be so that mass spectrometry works?
They need to be ionised to be detected
How does chromatography purify substances?
The substance that needs to be purified will be separated from other substances which makes it pure
Describe the process of paper chromatography
A pencil line is drawn 1 cm above the base of the filter paper with a ruler
The different substances are spotted onto the line at different points
Reference substances are also spotted onto the line
The bottom of the filter paper is dipped in solvent
The substances travel up the filter paper with the solvent and stop at different points forming a chromatogram
What are the 3 advantages of using machines for chemical analysis?
Can detect even the tiniest amounts of substances
Very fast and tests can be automated
Very accurate
What is the retardation factor?
How much a substance favours the mobile phase or stationary phase
1 for mobile and 0 for stationary
What does the height of a peak on the mass spectrum mean?
Each peak represents an ion
The higher the peak, the heavier the ion
What is gas chromatography?
A form of chromatography that uses a carrier gas as a mobile phase and is very accurate
Describe gas chromatography
The substances are heated until they become gases
The carrier gas brings the substances along a tube and they pass a sensor
The fact that they travel at different speeds means that they will go through the sensor at different times
What is the stationary phase?
The part of the chromatography equipment that does not move and is usually solid
What is chromatography?
A chemical process that separates mixtures of dissolved substances
What is the advantage of using thin layer chromatography instead of paper chromatography?
Small quantities of the substances can be used
What is a mass spectrometer?
An instrument that weighs molecules and tells us the molecular mass of substances
Why do we use reference substances?
So that we can see if some of the unknown substances are actually the reference substances
What is a mass spectrum?
The graph output of a mass spectrometer
What is a locating agent?
A chemical that reacts with a substance to form a coloured compound
What is the stationary phase in paper chromatography?
Filter paper
What is the retention time?
The time a substance takes to reach the detector
How do we know if an unknown substance and a reference substance are the same?
They will be level in height on the chromatogram
What is chemical analysis?
Analysing substances to find out their chemical composition and structure
What do we do to distinguish invisible spots?
Dip the filter paper in locating agent
What is a chromatogram?
The filter paper in paper chromatography with the spots at different heights after the chromatography has taken place
Why can’t some substances be detected by colour on the chromatogram?
They are colourless substances
How do you calculate the retardation factor?
Distance between spot and pencil line / distance between top of mobile phase and pencil line
How does chromatography find out which substances are present?
The substances are separated from each other meaning that they are pure so we can analyse which substances are present
Give the 2 uses of chromatography
Chemical analysis that finds out what the substances present are
Synthesis (purifying substances)
Which substances are used as carrier gases and why?
Argon and nitrogen
They are inert (don’t react)
Why do some substances move across the mobile phase at different speeds than each other?
Some substances have an equilibrium position that favours the mobile phase more or less than others
What is the mobile phase?
The part of the chromatography that pushes the substances across the stationary phase
What is retention?
How much a substance holds back (favours the stationary phase)
What is paper chromatography?
A type of chromatography where colours present in a substance travel up the paper at different rates
What is the mobile phase in paper chromotography?
Solvent
What is an empirical formula?
A formula that gives the simplest whole number ratio of atoms in a compound
What are the 7 factors that affect the sustainability of chemical production?
Feedstocks (renewable feedstocks needed)
Atom economy (high percentage)
Waste (minimised)
Energy in and out
Social and economic benefits (as much as possible)
Environmental impact (must be low)
Health and safety (processes can’t put workers in danger)
Describe how you calculate an empirical formula
Mass / relative atomic mass for each component
Divide each calculated number by the smallest of the 2 numbers calculated
Round to the nearest whole number
Put numbers into a ratio representing the components of the compound
The ratio should represent the number of atoms for the elements such as 1:2 being MnO^2
What is percentage yield?
The amount of product received compared with the amount of product expected
How could newly discovered chemicals be potentially hazardous?
We don’t know their long-term health effects yet so there are no hazard signs
Why is empirical formula used?
It is a quick and accurate estimate of the molecular formula
However, it isn’t always right
What is green chemistry?
The idea of making chemicals so that they endure the test of time and meet the needs of humans today and in the future
How do we make sure chemical processes are safe?
Hazard symbols
Regular checks
How do you calculate atom economy?
Molar mass of atoms in desired products / molar mass of atoms in reactants * 100 (percentage)
What are the 3 reasons that a percentage yield is under 100%?
The reaction is reversible (reactants never completely converted to products)
Filtration (you always lose some of the substances)
Unexpected reactions (there can often be other reactions happening that use up the reactants)
What is the formula for calculating percentage yield?
Actual yield / maximum theoretical yield * 100 (percentage)
How do you calculate the maximum theoretical yield?
Add together the molar masses of all the atoms in the reactants
The molar mass of an atom of the element should be the relative atomic mass in grams
Show how you would calculate the empirical formula of magnesium oxide? (The magnesium is 2g and the magnesium oxide is 3.25g)
3.25 - 2 = 1.25 2 / 24 (magnesium relative AM) = 0.0833 1.25 / 16 (oxygen RAM) = 0.0781 0.0781 is smallest 0.0781 / 0.0781 = 1 0.0833 / 0.0781 = 1.0665 1.0665 is rounded to 1 (nearest whole number So the ratio of the magnesium to the oxygen in the magnesium oxide is 1:1 This means the formula is MgO
How do you make polymers in a way that they will be more flexible?
High temperature and high pressure to make it more flexible
Why do nanoparticles have different properties to larger versions of the same material
The much larger surface area to volume ratio
What is a smart material?
A material that changes one of its properties depending on its conditions
Describe thermosoftening polymers
They don’t have cross-linking between chains so the chains are held together by weak intermolecular forces so they can slide over each other
Easy to melt
When it cools, the polymer hardens into a new shape
It can be melted and moulded again as many times as you like
What are fullerenes?
Molecules of carbon shaped like hollow balls or closed tubes
They can be joined together to make nanotubes
What is the most common natural nanoparticle?
Pollutants from burning fossil fuels
What is a nanoparticle?
A particle from 1 to 100 nanometres
What are the 7 uses of nanomaterials?
High surface area to volume ratio could help to make industrial catalysts
Can make sensors that detect only one type of molecule
Nanotubes can be used to make stronger and lighter building materials
Sun cream and deodorant made of nanoparticles don’t leave marks on the skin
Fullerenes are absorbed more easily by the body than other particles meaning that they could deliver drugs right into the cells they are needed
New lubricant coatings that massively reduce friction
Nanotubes conduct electricity so they could be used in tiny electric circuits
What is a nanometre in comparison to a metre?
A billionth of a metre
What is nitinol and what is it used for?
A shape memory alloy that returns to its original shape when heated
Used for braces because the heat of the mouth causes it to return to its original shape and gently pull the teeth in
Describe thermosetting polymers
They have stronger intermolecular forces called cross links that hold the chains firmly together
Doesn’t soften when heated
Strong, hard and rigid
What are the melting and boiling points of simple covalent substances like?
Usually gases or liquids at room temperature
What are the 4 properties of metals?
Free electrons allow conduction of heat and electricity
They are strong because of the strong electrostatic attractions between the positive metal ions and negative electrons
The regular arrangement allows layers of atoms to slide over each other allowing metals to be bent and shaped
What are simple covalent substances?
Where small covalently bonded compounds are held together by very weak intermolecular forces
Describe metals
Metal atoms lose their outer electrons to their surroundings
If many metal atoms are together, the sea of delocalised electrons is enough to hold the atoms together in a regular structure
Do simple covalent substances conduct electricity and why?
No
Because there are no freely moving charged particles
Describe diamond
Each carbon atom forms four covalent bonds in a very rigid giant covalent structure
This makes diamond the hardest natural substance
What are giant covalent substances?
Covalent structures where all atoms are bonded to each other by strong covalent bonds
Describe graphite
Each carbon atom only forms 3 covalent bonds which creates layers that are free to slide over each other
Each carbon atom has one delocalised electron that is between the layers and holds them together (weak intermolecular forces)
Graphite is soft because the layers are free to slide over each other because of the weak intermolecular forces
Good conductor of electricity and heat because of the delocalised electrons
What are the 3 properties of giant covalent structures?
High melting and boiling points (strong bonds)
Never conduct electricity (except for graphite)
What happens when simple covalent substances melt or boil?
The intermolecular forces are broken and no harm comes to the covalent bonds
How do you draw a dot and cross diagram for covalent bonding?
Draw a Venn diagram
Only draw the outer shells unless question asks otherwise
Put dots on one atom and crosses on the other
Put the required amount of the those dots and crosses in the overlap so that both atoms have a full outer shell
Describe covalent bonding
Non-metals share electrons in their outer shells
This means that both atoms feel that they have a full outer shell
They are held together because the shared electrons are attracted by both nuclei
Describe silicon dioxide
Sometimes called silica and it is what sand is made of
Each grain of sand is one giant structure of silicon and oxygen
What can ionic bonds form between?
Only metals and non-metals
How do you show ions by drawing their electronic structure?
Draw the electronic structures of the original atoms
Get rid of lost electrons and add gained electrons to the drawings
Put square brackets around each drawing and put the charge after the brackets of each ion
What are the 4 main properties of ionic compounds?
High melting and boiling points due to the strong force of attraction
They dissolve easily in water
Melting ionic compounds or putting them into solution lets the ions freely move so they can conduct electricity
How do you calculate the reaction for an ionic compound?
Look at the charge of the positive ion and look at the charge of the negative ion
Calculate how many of each ion is needed to get an overall charge of 0
The number of ions will be the subscripts in the ionic compound
Describe ionic bonding
Atoms on the left side of the periodic table lose the electrons in their outer shell so that they have a full outer shell (they now have more protons than electrons so they have a +ve charge)
Atoms on the right side gain the electrons that the other atoms lost in order to get a full outer shell (they have a -ve charge because they now have more electrons than protons)
The opposite charges of the 2 ions hold them together as a compound
Describe the structure of ironic compounds
Ionic compounds always have giant ionic lattices
The ions form a closely packed regular lattice arrangement
There are very strong electrostatic forces of attraction between oppositely charged ions in all directions
What do you do if there is brackets in the formula unit?
Calculate the relative formula mass of the contents of the brackets and multiply that by the number after the bracket
Why is the relative atomic mass of chlorine 35.5?
The 35.5 is an average
75% of chlorine is 35 and 25% is 37
Why do isotopes chemically behave in the same way as each other?
Chemical reactions are determined by the number of electrons
What is an element?
A substances where all atoms contain the same number of protons
How do you calculate relative formula mass?
Add together the relative atomic masses of every atom in the compound
How do you work out how much 1 mole is of a substance?
1 mole is the relative atomic mass or relative formula mass in grams
What is the atomic number?
The number of protons in the element
Show how would calculate the relative formula mass of water
In water, there is one oxygen and 2 hydrogens
16 + (2 * 1) = 18
The relative formula mass of water is 18
What is the molar mass?
Another term for relative formula mass or relative atomic mass
How do you calculate relative atomic mass?
Multiply mass number of isotope by its abundance for each isotope
Add them all together
Divide by 100
What is the mass number?
The total number of protons and neutrons
If we know the relative formula mass of water is 18, how much is 1 mole of water?
18g
What is relative formula mass?
A way of calculating the mass of a compound compared to other compounds and elements
What is relative atomic mass?
An average of the mass numbers of all isotopes of an element
What is a formula unit?
When calculating relative formula mass, the formula unit is the compound we are calculating the relative formula mass of
What are isotopes?
Variants of an element that have the same number of protons and electrons but a different number of neutrons
Why are the physical properties of isotopes different?
The different numbers of neutrons will cause the masses of the different isotopes to be different
