AQA Chemistry
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AQA Chemistry - Details
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297 questions
| 🇬🇧 | 🇬🇧 |
| What is an element | Contains only one type of atom e.g. Mg, S, K |
| What is a compound | Two or more different elements that are chemically combined |
| Are the properties of compounds the same as the element they are made from? | No they have completely different properties |
| How do we separate a compound back into its elements | A chemical reaction |
| What is an atom | The smallest possible unit of an element |
| What is a mixture | Different elements or compounds that are not chemically combined |
| How do we separate a mixture | Using physical techniques |
| What are examples of a physical technique | Filtration, distilation, chromatogrpahy etc |
| What is a molecule | Any element chemically joined |
| MgS | 1 atom of magnesium 1 atom of Sulphur |
| Na2SO4 | 2 atoms of sodium 1atom of Sulphur 4 atoms of Oxygen |
| What happens if we change the number of atoms in a specific compound | We get a whole new compound |
| How do we separate compounds back into their elements | Chemical reaction |
| Name all the key features of a chemical reaction | 1) compounds are broken up or formed 2)at least one new substance is created 3) no atoms are created or destroyed 4)measurable energy change |
| What happens to the chemical properties of a mixture | Doesn't change because they have been mixed with another substance |
| Give me two examples of a mixture | 1) Air (mix of oxygen-nitrogen and co2 2) A bowl with pasta and vegetables |
| What is filtration | Separates an insoluble solid in a liquid |
| What does insoluble mean | The solid wont dissolve in a liquid |
| How do we filter an insoluble solid | We need a filter funnel and filter paper 1)Pour the mixture into the filter paper The liquid passes through while the solid is trapped |
| What is crystalisation | Separate a soluble solid from a liquid |
| What does solvent mean | Liquid |
| Give me a benefit of evaporation | Quick and easy to separate the soluble solid from liquid |
| Give me a disadvantage of evaporation | Some solids decompose when heated(thermal decomposition) |
| How do we use evaporation to separate a soluble solid from a liquid | 1) Pour mixture into an evaporating dish 2) place on top of the tripod 3) Then slowly heat with bunsen burner This cause the solvent to start evaporating and the solution to become more concentrated forming crystals |
| How do we use crystallization to separate a soluble solid from a liquid | 1) Pour mixture into an evaporating dish 2) Heat with a water bath Once we see crystals start to form we stop heating it and take out the water bath and let it cool 3) Then filter and dry |
| Why do we leave it out to cool | Because solids are less soluble at colder temp |
| Steps of crystalisation | 1) Gently heat the mixture till the solvent evaporates 2) Crystals of the solid will start to form |
| What was Thomsons plum pudding model | - discovered electrons in 1897 - a ball of positive charge with electrons mixed in with the dough |
| What was Rutherfords nuclear model | - discorved an atoms mass is concentrated in centre - and contained protons |
| What was Niels Bohr discorvery | - electrons orbit the nucleus - some particles have no charge and he called it neutrons |
| Charge of sub atomic particles | Protons - +1 (mass of 1) electrons - -1(mass very small) neutrons - 0 (mass of 1) |
| What is simple disilation | Separates out a liquid from a solution and also 2 liquids with different boiling points |
| How does it work | 1)Place the solution into the flask 2)Heat the solution which causes the liquid to evaporate turning into a vapor 3)The vapor rises up the glass tube 4)The vapor then passes into the condenser where it turns back to a liquid 5)Collect the liquid in a beaker so at the end we're left with a solid in the flask and liquid in the beaker |
| Why is a thermometer used in simple distillation? | To make sure that the highest boiling point isnt exceeded otherwise both liquids would boil and wouldnt be seperated |
| What is fractional distillation used for | Separte a mixture of different liquids with different boiling points |
| Describe a method for making pure crystals of magnesium chloride from magnesium and dilute hydrochloric acid. | 1) Add a fixed volume of hydrochloric acid to the beaker 2) add small pieces of magnesium ribbon until its in excess so all the acid as reacted 3) filter out any excess magnesium using filter paper and funnel 4) add solution to an evaporating basin 5) heat with a bunsen burner until it starts to crytsalise 6) pat dry the crystals on paper towels |
| What are hydrocarbons | Molecules containing hydrogen and carbon atom only |
| How is crude oil formed | From the remains of fossiled planktons |
| Where is crude oil found | In rocks |
| What is crude oil used for | To produce fuels and other useful chemicals |
| What is crude oil a mixture off | Lots of different compounds that are not chemically combined |
| Why do heavy fractions of crude oil not make good fuels | 1) Low volatility 2) Don't ignite easily 3) Have high boiling points |
| What are the bonds of carbon in alkanes | Carbon atoms bond to four other atoms(either hydrogen or carbon) |
| Why are alkanes called saturated | Because they only contain a single bond with other atoms |
| What are alkanes used for | They're quiet unreactive but can burn well so they make good fuels |
| Name the 4 smallest hydrocarbons in order | 1) Methane 2) Ethane 3) Propane 4) Butane |
| What do the hydrocarbon size affects | Its properties |
| What do the hydrocarbon properties affect | How useful it is as a fuel |
| Give me the properties of Longer chained hydrocarbons | - Higher viscosity(flow less easily) - Less flammable - Higher boiling point |
| What does the equation for the combustion of hydrocarbons depend on | The amount of oxygen available |
| What happens to the combustion of an hydrocarbon in a good supply of oxygen | - Energy released - C02 + H20 created |
| What happens to the combustion of hydrocarbons in a lack of oxygen | - Carbon monoxide is created |
| Give me the properties of a short chained hydrocarbon | - Highly volatile - Ignite easily - Low boiling points |
| What is fractional distillation | Process of separating crude oil into fractions |
| How does fractional distillation separate hydrocarbons | Using their boiling points |
| Describe the process of FD | 1) Crude oil is evaporated - the vapors are put into the fractionating column at the bottom and raises upwards 2) Long chained HC condense at the bottom due to the high BP - SC HC condense nearer to the top due to it being highly volatile 3) The fractions are collected then processed to create products (petrol, diesel, etc) |
| What is cracking | Breaks down longer chained hydrocarbons into smaller more useful molecules |
| Steps to catalytic cracking | - Vapourised hydrocarbons passed over hot catalyst - The product includes alkanes and alkenes |
| Steps to steam cracking | - Vapourised HC mixed with steam at high temp - Products include alkanes and alkenes |
| Name the uses of alkenes | - combined to make polymers - starting material for chemicals like ethanol |
| What is a pure substance | Single element or compound |
| How do we work out purity | - By looking at melting and boiling points of samples - pure have exact and specific melting and boiling points |
| What are some examples of pure substances | Water, glucose, oxygen, sodium chloride etc |
| Impurities effect on melting point | Lower melting point Increase range of temp that the sample will melt |
| Impurities effect on boiling point | - increase boiling point - increase range of temp at which sample will boil |
| What is a formulation | Mixtures of chemicals that are designed to create more useful products |
| Quantity of each component in a formulation | To ensure that the formulation does its job, each component must be present in a precisely measured quantity |
| Give me an example of a formulation | Metal alloys, medicines and fertilisers |
| Pure substances on melting and boiling | Only pure substances melt and boil at specific temperatures |
| What does water boil at | 100 degrees celcius |
| What does sodium chloride melt at | 801 degree celcius |
| What is aa physical test | Testing the ohysucal proepeties of a substance |
| Impure substances on melting and boiling | They melt and boil over a range of temperatures depending on how much of each substance is in the mixture |
| What is chromatography | Separates mixtures into its different components |
| Impurities on melting and boiling point | - lower melting point - increase boiling point |
| What are the two phases of chromatography | Phase 1 - Substances picked up and carried by a mobile phase(liquid or gas) phase 2 - Mobile phase moves into a stationary phase (solid or viscous liquid) |
| Quantity of each component in a formulation | Each chemical component must be measured in precise quantity to ensure that the formulation works |
| In chromatography, will a substance move further if it is more attracted to the mobile or stationary phase? | More attracted to the mobile phase |
| Equation for Rf value | Distance travelled by substance/ distance travelled by solvent |
| What is chromatography | Analytic technique used to separate different substances from mixtures |
| Paper chromatography experiment | 1) Take filter paper and draw a line near the bottom(baseline) 2) Add a sample of ink to the pencil line 3) Add a shallow amount of solvent to the beaker 4) Then place filter paper into solvent but make sure it doesn't submerge the pencil line 5) Wait for the solvent to seep up the paper, then the different dies which make up ink will dissolve and rise with it 6) Take out the paper and leave it to dry |
| How does each die travel | At different rates - each one must be a different substance |
| What is the mobile phase | Substances the molecules can move in e.g. liquid or gas |
| What is the stationary phase | Substance the molecules cant move in e.g. viscous liquid or solid |
| Chemicals more soluble in solvent | Spend more time in mobile phase therefore moving faster |
| Chemicals less soluble | Spend more time in stationary phase therefore moving more slowly |
| What is a reference substance | A pure sample that runs alongside the unknown mixture to see if its a component in the mixture |
| How do we test for Hydrogen | - Hold a lit splint at the end of a test tube containing a gas - If its hydrogen a squeaky pop will be let off |
| How do we test for oxygen | - Insert glowing splint into test tube containing a gas - If gas is oxygen the splint will relight |
| Testing for carbon dioxide | - shake carbon dioxide with calcium hydroxide - The solution will turn from clear to cloudy |
| Testing for chlorine | - damp litmus paper into test tube containing a gas - If the gas is chlorine the litmus paper will change from red to white |
| How are elements arranged in periodic table | By atomic number |
| What do elements in the same column have in common | Same amount of electrons in the outer shell |
| Predicting chemical properties | Because elements in the column have same number of electrons in their outer shell, they have similar chemical properties and will react in similar ways |