AQA GCSE Additional Science Chemistry

Frage	Antworten
How do you find out the charge of an ion?	LOOK AT ITS GROUP NUMBER Group 1 = 1+ (needs to lose 1) Group 2 = 2+ (needs to lose 2) etc. so all +vely charged up to group 5. Group 6 = -2 Group 7 = -1
What is an ion?	An atom that has lost/gained electrons.
What is a reversible reaction?	A reaction in which the products can re-form the reactants. Can never get a 100% percentage yield.
What is the rate of a reaction?	The change in concentration of a reactant or product in a given time.
How does increasing the temperature affect the rate of reaction?	Particles will have more energy and move quicker. (in metals - ions vibrate more) so will collide with more energy. Higher frequency of successful collisions so reaction will be faster.
How does increasing the concentration affect the rate of a reaction?	More particles per unit of volume, higher frequency of collisions, faster reaction.
How does increasing the pressure increase the rate of a reaction?	More particles within a given volume, higher frequency of collisions, faster reaction.
How does increasing the SA increase the rate of a reaction?	More space to react, higher frequency of successful collisions, so reaction is faster.
Acid + metal --> ??+???	Salt and Hydrogen
Acid + Alkali --> ??+?? Acid + Base --> ??+??	Salt + water.
How to make insoluble salts.	Add lead nitrate to potassium iodide. Ions in the 2 solutions react. (Pb^2+ and I^-) Lead iodide is created. Lead iodide is insoluble (it's a solid precipitate) so it precipitates out of solution. Filter precipitate. Wash (e.g. w/distilled water) and dry precipitate.
How to extract aluminium	Aluminium oxide is electrolysed. Cryolite is mixed with aluminium oxide to lower its melting point by around 1/2. Al forms at -ve electrode. Ocygen formed at +ve electrode. +ve carbon electrodes replaced regularly as they react with oxygen to form CO2 and gradually burn away.
Why would the calculated yield of a reaction not be obtained?	Not fully reacted. Gases lost to air. Impurities in the reactants.
How to make Soluble Salts Using Acid + Insoluble Base -> (soluble) Salt + Water	Add copper oxide (IB) to sulphuric AcCID. Warm and stir mixture until reaction is over i.e. some copper oxide's left. Filter solution through filter paper. Add copper sulphate solution to evaporating dish over beaker of water. Heat beaker. leave to sit for a few days. Copper sulphate will evaporate.
What is collision theory?	The reacting particles need enough energy (the activation energy) to react when they collide.
What is the activation energy?	The smallest amount of energy that particles must have before they can react.
3 Advantages of Using Catalysts	1. Cheaper to use a catalyst than to pay for extra energy required for higher temperatures/pressures. 2. They can be used over and over again without being used up or chemically changed. 3. Can lower production costs for making particular products.
2 Disadvantages of Using Catalysts	1. They're often very expensive metals e.g. gold or platinum 2. They're often transition metals or their compounds, which are often toxic and can harm the environment if they escape.
How would you measure the rate of a reaction?	The amount of reactant used/time The amount of product formed/time
4 Developments of Using Catalysts in Industry	1. Chemists are working to develop new catalysts that are harmless to the environment. 2. They can now follow the reactions that happen on the surface of metals in a catalytic converters. Knowing how they take place will help them design new catalysts. 3. Chemists can now make catalysts used in making drugs without the precious metal. 4. Enzymes can be used as catalysts.
What are exothermic reactions?	Energy is transferred FROM the reacting chemicals TO their surroundings. Energy transferred heats up the surroundings; there is a rise in temperature.
What are endothermic reactions?	Energy is transferred FROM the surroundings TO the reacting chemicals. There is a drop in temperature.
3 Examples of Exothermic Reactions	1. Respiration 2. Neutralisation 3. Combustion
Example of an Endothermic Reaction	Thermal decomposition
How can we use the energy from exothermic reactions in a disposable hand warmer?	Oxidation of iron releases energy. Iron turns into hydrated iron oxide in an exothermic reaction. NaCl is used as a catalyst. Can only be used once but lasts for a few hours.
How can we use the energy from exothermic reactions in a reusable hand warmer?	Based on formation of crystals from solutions of a salt (often sodium ethanoate). A supersaturated solution is prepared. We do this by dissolving as much of the salt as possible in hot water and allowing the solution to cool. Small metal disc in plastic pack starts exothermic change. When pressed, small particles of metal are scraped off, starting crystallisation which give out energy.
How would you re-use a reusable hand warmer?	Put solid back into boiling water to re-dissolve the crystals and wait for it to cool down.
How can we use the energy from exothermic reactions in self-heating cans? Give some disadvantages.	Press button in base of can. This breaks seal, allows water and calcium oxide to mix. Development took years and cost millions of pounds. In early versions, temperature of coffee didn't rise high enough.
How can we use cooling effect of endothermic reactions in cold packs for sports injuries? (can also be used to chill drinks cans)	Chemical cold packs contain ammonium nitrate and water. Ammonium nitrate dissolves and takes in energy. Advantages:: Are ideal where there is no ice available to treat knock/strain. Disadvantages: Can only be used once
What's the name of the substance broken down in electrolysis?	The electrolyte
What is formed in the electrolysis of brine (sodium chloride and water)? Where are these substances formed?	Hydrogen - at the -ve electrode as formed from H+ ions. Chlorine - at the +ve electrode as formed from Cl- ions. Sodium Hydroxide solution
Test for Hydrogen 3 Uses of Hydrogen	Produces squeaky pop with lit splint As a fuel, to make ammonia, harden margarine
Test for Chlorine Uses of Chlorine	Bleaches damp litmus paper. Sterilises swimming pools
Test for Sodium Hydroxide Uses of Sodium Hydroxide	Litmus paper turning paper, showing it's alkaline Oven cleaner and making bleach
What are acids?	Substances that produce H+ ions when we add them to water.
What are bases?	Substances that will neutralise acids. They include alkalis, metal oxides and metal hydroxides.
What are alkalis?	A soluble hydroxide. A base that can dissolve in water. Produce OH- ions when we add them to water.
Why do we electroplate objects? 3 reasons	To improve their appearance To protect their surface To use smaller amounts of precious metals.
Explaining Electroplating (What should be used as each electrode, what happens at each electrode)	The object to be plated should be the -ve electrode. The object you'll plate it with should be the +ve electrode. At +ve electrode: Atoms are oxidised. Form nickel ions which go into the solution. At -ve electrode: Ions from solution are reduced. Form atoms which are deposited on the electrode.
How to Make Soluble Salts (using Acid + Alkali -> Salt + Water)	Measure out how much alkali you want. Flask contains alkali and indicator. Add acid until indicator goes green, while measuring how much acid you've added. Repeat experiment without indicator, adding the right amount of acid and alkali. We know solution is now neutral. Put solution into evaporating dish and heat above beaker of water. Leave solution for few days on side to form into salt crystals.
Uses of Precipitation Reactions	Treating Effluent (waste produced by factories): Reacts ions to produce a solid substance that can then be filtered
What is the +ve electrode called?	The anode
What is the -ve electrode called?	The cathode
What happens at the +ve electrode?	Oxidisation -ve ions lose electrons.
What happens at the -ve electrode?	Reduction +ve ions gain electrons.

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