Chemistry Flashcards
1
Q
Relate the uses of nanoparticulate materials to their properties
A
- Nanoparticulate titanium dioxide is used in sunscreens as it’s particles are very small, so is transparent but still absorbs UV radiation
- Nanoparticulate materials can also be useful as catalysts, for example in catalysing the breakdown of dirt in stain-resistant clothes. This is because of their large SA:V ratio.
2
Q
Explain some risks of nanoparticles
A
- They are very small, so can be breathed in and pass through the skin
- They have a large SA:V ratio, therefore can catalyse harmful reactions and carry toxic substances. This may cause various health issues.
3
Q
Recall some physical properties of ionic solids
A
- Ionic compounds have high melting points and boiling points due to strong electrostatic forces of attraction that require lots of energy to break.
- Ionic compounds are hard and brittle.
- They are locked into a lattice, therefore unable to conduct electricity
4
Q
Compare the sizes of nanoparticles, atoms and molecules
A
- Nanoparticles are larger than atoms and simple molecules.
- Nanoparticles typically consist of just a few hundred particles, and are 1-100nm insize, whilst e.g an oxygen atom is 0.1nm in diameter.
5
Q
State the fractions of crude oil and their uses
A
- From top to bottom
- Gases –> domestic heating and cooking
- Petrol –> fuel for cars
- Kerosene –> fuel for aircrafts
- Diesel –> fuel for some cars and trains
- Fuel Oil –> fuel for large ships and power stations
- Bitumen –> surfacing raods and roofs
6
Q
Why is crude oil so important in the petrochemical industry?
A
Petrochemicals are substances made from crude oil, such as polyethene and other polymers.
Crude oil is the source of feedstock (raw materials) for the petrochemical industry.
7
Q
What is crude oil?
A
- Crude oil is a complex misture of hydrocarbons. These are compounds that contain hydrogen and carbon atoms ONLY.
8
Q
Describe the trends in the properties of crude oil fractions in terms of:
- Number of atoms in molecules
- Boiling points
- Ease of Ignition
- Viscosity
A
- The number of atoms in molecules increase from top to bottom (bitumen is the longest)
- The boiling points increases from top to bottom (bitumen has the highest b.p)
- The ease of ignition deceases from top to bottom (bitumen is the most difficult to ignite)
- The viscosity (thickness) increases from top to bottom (bitumen flows with the most difficulty)
9
Q
Why do the fractions of crude oil differ in properties?
A
- They all contain differing numbers of carbon atoms in molecules
- The greater the carbon atoms, the more covalent bonds and intermolecular forces that need to be overcome, so boiling points increase as chains increase.
10
Q
Describe the main features of a homologous series
A
- They have the same general formula
- They have similar chemical properties
- The molecular formulae of neighbouring compounds differ by CH2
- They show a gradual variation in physical properties
11
Q
Explain why alkanes form a homologous series
A
- They share a general formula, CnH2n+2
- They have similar chemical properties, for example they react with excess oxygen to produce carbon dioxide and water.
- There is gradual variation of physical properties, longer chain alkanes have greater boiling points.
12
Q
Explain why ethanol production from carbohydrates are carried out at around 35o C rather than higher themperatures of 70oC and above.
A
- Ethanol is made from seeds - these contain the carbohydrate starch. This starch needs to be broken down into sugars in order to make ethanol.
- Enzymes in the seeds naturally turn the starch into sugars. If temperatures are too high (e.g over 70o C) then the enzyme could denatured, and the starch wouldn’t be broken down into glucose
13
Q
How are carboxylic acids formed?
A
- The oxidation of alcohols
- This often involves oxidising agents, typically a base like copper oxide
14
Q
State the names, formulae and structures of the first four members of the carboxylic acid series
A
15
Q
What is the functional group present in all carboxylic acids?
(draw it)
A
-COOH
16
Q
Describe a method to compare the heat of combustion of the first five alcohols
A
In the textbook’s method, we measure the temperature rise of a known mass of water caused by the combustion of methanol, ethanol, propanol, butanol, and pentanol.
- Measure the mass of an alcohol burner and cap, record the mass
- Place the alcohol burner in the centre of a heat proof mat
- Use a measuring cylinder to add 100cm3 of cold water to a conical flask
- Measure and record the initial temperature of the water and clamp the flask above the alcohol burner
- Light the wick of the alcohol burner and allow the water to heat up by about 40oC
- Replace cap on the burner, measure and record final temperature o the water
- Measure the mass of alcohol burner and cap again, record the mass
- Calculate the mass of alcohol burned to produce a 1oC rise in temperature, by using the temperature difference
Note that in Mr Ade’s method:
We let the water heat to 100oC, then calculate the change in mass. Measure spirit burner before and after (mass). Change in mass is the amount of fuel used to heat the water to 100oC.
CONTROL FACTORS:
- volume of water
- height of flask above wick
SOURCES OF ERROR:
- heat loss to the surroundings –> we use insulation
- measuring mass
- measuring temperature
- measuring volume of water
17
Q
Compare and contrast the gases in the early atmosphere with that in today’s
A
SIMILARITIES
- Contained both CO2 and water vapour
DIFFERENCES
- Little to no oxygen in the early atmosphere, photosynthesis caused it to increase
- Proportion (not amount) of CO2 is much less since it was used in photosynthesis and dissolved in oceans
18
Q
What has caused variations in CO2 in today’s atmosphere?
A
INCREASE
- Combustion of fossil fuels has released CO2
- Deforestation has reduced the amount of plantst taking in CO2
DECREASE
- Used up in photosynthesis
- Dissolved in oceans
19
Q
Explain why most simple molecular covalent compounds have low boiling points
A
- Despite the strong covalent bonds inbetween individual atoms, there are weak intermolecular forces between each molecule.
- A low amount of energy is required to overcome these weak forces, therefore they generally have lower boiling points
20
Q
How many particles are present in 1 mole of any substance?
A
6.02 x 1023
21
Q
What would you observe when you put lithium, sodium and potassium in water that contains universal indicator?
A
- Li: Bubbling fiercely on the surface and moves around a bit. Water turns purple
- Na: Melts into a ball and fizzes about the surface Water turns purple
- K: Bursts into flames and flies about the surface. Water turns purple.
- Effervesance/bubbling indicates the presence of a gas (hydrogen)
- Water turns purple becuase it is alkali (metal hydroxide forms)
- Increased speed indicates a higher rate of reaction
22
Q
Explain the trend in reactivity of alkali metals as you go down the group
A
- Alkali metals contain 1 electron in their outer shell, so their reactivity is measured upon their tendency to lose this outer electron
- As you go down, atoms get larger as we add electron shells
- The force of attraction between the positive nucleus and the negative outer electron decreases as they become further apart
- Therefore, as we go down the group, there is a weaker force of attraction between the outer electron and the positive nucleus so it’s easier to remove the outer electron.
23
Q
How do you calculate relative atom mass?
A
- (mass 1 x abundance 1) + (mass 2 x abundance 2)
- DIVIDED BY 100
24
Q
Why are alkenes considered unsaturated?
A
- They contain a carbon double bond, which can split and form new bonds.
25
What does complete combustion produce?
Carbon Dioxide and Water
26
Describe the test for alkenes/alkanes
* When placed in and mixed with bromine water, an alkane won't react and no change will be observed
* However, the double bond in an alkene, will open out and react with the **bromine wate**r taking it out of the water and it goes from **orange-brown to colourless**
* This forms 1,2 dibromo-ethane
27
Why are some reations exothermic and others endothermic?
(in terms of bond breaking / bond making)
* Energy is transferred to the reactants to break their bonds, so breaking bonds is endothermic
* Energy is transferred from the reactants to the surroundings to form bonds, so making bonds is exothermic.
28
How do
1) Temperature
2) Concentration
3) Surface Area
Affect the rate of reaction?
1. An increase in temperature gives the reactant particles more kinetic energy meaning they move around more. This means there will be more frequent successful collisions and more particles will have the required level of energy to react
2. An increase in concentration means more particles in a fixed volume
This means that that successful collisions will be more frequent as particles are closer together
3. More surface area leaves more of the surface exposed. This means that collisions have more surface to occur on and so successful ones occur more often
29
Describe a positive test for
1) Chlorine
2) Hydrogen Gas
* Chlorine, if present, will turn damp blue litmus paper red, then bleach it white
* We can carry out a squeaky pop test to test for hydrogen - we light a splint, then place it near the gas. If Hydrogen is present, it extinguishes and produces a pop sound.
30
What do hydrogen halides produce in solution when dissolved?
* ACIDS
For example, hydrogen chloride dissolves to form hydrochloric acids.
Hydrogen fluoride dissolves to form hydrofluoric acid. etc.
31
Predict the trend in state and colour change as you go down the halogen group.
* As you go down the halogen group, boiling point / melting point will increase and the colour becomes darker.
* For example, chlorine has a b.p of -34, and is a green gas. If you go down, iodine has a bp of 184 but is a purple/black solid.
32
Explain how the order of reactivity of halogens can be worked out from displacement reactions
* We can carry out displacement reactions, where a more reactive element takes the place of a less reactive leemnt.
* Therefore, a more reactive halogen displaces a less reactive halogen from a halide compound.
* E.G Chlorine can displace bromine from sodium bromide in solution.
33
State what observation you would make in each of these reactions signifying that displacement has taken place:
1. Fluorine + Potassium chloride
2. Chlorine + Potassium bromide
3. Bromine + Potassium iodide
1. Solution turns yellow showing that chlorine has been produced
2. Solution turns orangey-brown showing that bromine has been produced
3. Solution turns dark brown showing that iodine has been produced
34
Why is displacement a redox reaction?
* Because both oxidation and reduction occur at the same time.
* e.g 2Cl- + F2 → Cl2 + F-
* The chlorine loses electrons at the same time that the fluorine gains electrons and so it is a redox reaction
35
What do halogens produce when they react with metals?
* Halogens form halide salts.
36
What colours do these metal ions appear during a flame test
1. Lithium
2. Sodium
3. Potassium
4. Calcium
5. Copper
1. Red / Crimson
2. Yellow
3. Lilac
4. Orange-Red
5. Blue-Green
37
How do we use flame photometer data to identify metal ions?
* Flame photometers can separate a mixture of colours into a spectrum.
* Different metal ions produce different emission spectra, which can be matched to a known ion
38
What colour do these metal hydroxides appear as?
1. Iron II
2. Iron III
3. Copper
4. Calcium
5. Aluminium
1. green
2. brown
3. blue
4. white
5. white
39
How do we use sodium hydroxide solution in these precipitation reactions?
* A few drops of sodium hydroxide are added to a solution containing metal ions
* The metal and the hydroxide will react to form metal hydroxide
* This will be insoluble and form a precipitate of a colour that can be used to identify the metal
40
How do you test for sulphate ions?
* Add some dilute hydrochloric acid to the solution
* Then add barium chloride If sulfate ions are present, this will produce a white precipitate of (insoluble) barium sulfate
41
How do you test for halide ions?
* Add some dilute nitric acid to your sample
* Add some silver nitrate solution
* Observe the colour of the precipitate formed and compare to check what ion was present
42
How do you test for ammonium ions and ammonia?
* Dilute sodium hydroxide solution is added which produces ammonia gas
* Ammonia gas has a characteristic sharp smell but a confirmatory test is needed to be sure
* Ammonia gas turns damp red litmus paper blue
43
What colours do each of these halide ions form in precipitate?
* Chloride
* Bromide
* Iodide
1. white
2. cream
3. yellow
