AQA GCSE Chemistry: Chemical Changes and Reactions

What is the general formula for the reaction between an acid and a metal?

acid + metal → salt + hydrogen

What is the general formula for the reaction between an acid and a metal oxide?

acid + metal oxide → salt + water

What happens during a neutralisation reaction between an acid and an alkali?

A salt and water are produced.

What is produced when an acid reacts with a carbonate?

Salt, water, and carbon dioxide.

What is the general formula for the reaction between an acid and a carbonate?

acid + carbonate → salt + water + carbon dioxide

What is the pH of neutral solutions?

pH 7, which are neither acids nor alkalis.

What do acids produce in aqueous solutions?

H⁺ ions.

What do alkalis produce in aqueous solutions?

OH⁻ ions.

What is a redox reaction?

A reaction where both oxidation and reduction occur simultaneously.

What do metals produce when reacted with water?

A metal hydroxide and hydrogen.

What do metals produce when reacted with acids?

A salt and hydrogen.

What is oxidation in terms of electron transfer?

Loss of electrons.

What is reduction in terms of electron transfer?

Gaining of electrons.

What occurs when a more reactive metal displaces a less reactive metal?

The more reactive metal will replace the less reactive one in a chemical reaction.

What is the role of hydrogen ions in neutralisation reactions?

They react with hydroxide ions from an alkali to produce water.

What is the ionic equation for the reaction of hydrogen ions with hydroxide ions?

H⁺ + OH⁻ → H₂O.

What is produced when lithium reacts with water?

Lithium hydroxide and hydrogen.

What is the ionic equation for the reaction of calcium with dilute acid?

Ca → Ca²⁺ + 2e⁻.

What is the mnemonic used to remember the order of the reactivity series?

Purple (potassium), slime (sodium), can (calcium), make (magnesium), carbon, a (aluminium), zebra (zinc), insane (iron), try (tin), learning (lead), how (hydrogen), camels (copper), surprise (silver), gorillas (gold), nitric (nitrate), sulfuric (sulfate).

What happens during electrolysis?

Opposites attract.

What is the result of a reaction between sodium and hydrochloric acid?

Sodium chloride and hydrogen.

What is electrolysis?

Electrolysis is the splitting up of an ionic substance using electricity.

What happens to ions during electrolysis of molten lead bromide?

The positive lead ions are attracted toward the negative electrode (cathode) and gain electrons, while the negative bromide ions are attracted toward the positive electrode (anode) and lose electrons.

What is the difference between strong and weak acids?

A strong acid completely dissociates in solution, while a weak acid only partially dissociates.

Provide an example of a strong acid and its dissociation in solution.

Hydrochloric acid (HCl) completely dissociates into hydrogen (H⁺) and chloride (Cl⁻) ions.

What is the role of the anode and cathode in electrolysis?

The anode is the positive electrode where oxidation occurs, and the cathode is the negative electrode where reduction occurs.

What is oxidation in terms of electron transfer?

Oxidation is the loss of electrons.

What is reduction in terms of electron transfer?

Reduction is the gain of electrons.

What does the double arrow symbol in dissociation equations indicate?

The double arrow symbol indicates that the reaction is reversible.

What is the process for making soluble salts from acids?

1. Make a saturated solution by stirring the acid with a base. 2. Filter the solution to remove excess solid. 3. Heat the solution to crystallize the salt.

What is the significance of the reactivity series in electrolysis?

The reactivity series determines whether hydrogen or a metal will be produced at the cathode during electrolysis.

What happens when a metal is more reactive than hydrogen in electrolysis?

If the metal is more reactive than hydrogen, hydrogen will be produced at the negative cathode.

What is the half equation for the reduction of lead ions during electrolysis?

Pb²⁺ + 2e⁻ → Pb.

What is the purpose of using half equations in electrolysis?

Half equations represent what is happening at the electrodes during electrolysis.

What is the first step in setting up an electrical circuit for electrolysis?

Two electrodes must be placed in the electrolyte.

What is the effect of heating water in the process of making soluble salts?

Heating water helps to dissolve the acid and base to form a saturated solution.

What is the final step in the crystallization process of making soluble salts?

Once cooled, pour the remaining liquid into a crystallizing dish and leave to cool for 24 hours.

What is the general outcome when ions reach the electrodes during electrolysis?

The ions lose or gain electrons and become neutral elements.

What is the importance of the process of electrolysis in metal extraction?

Electrolysis is used to extract metals that are too reactive to be extracted by reduction with carbon.

What is the relationship between the energy used and the extraction of metals by electrolysis?

Large quantities of energy are used to melt the compounds during the extraction process.

What is the effect of stirring a solution while making soluble salts?

Stirring helps to dissolve the solid until no more will dissolve, creating a saturated solution.

Why are ionic substances unable to conduct electricity when solid?

When solid, the ions in ionic substances are fixed in place and cannot move to carry a charge.

What happens to the charges of ions when they reach the electrodes?

The charges are lost, and the ions become neutral elements.

What is the significance of the term 'OIL RIG' in electrolysis?

OIL RIG stands for 'Oxidation Is Loss, Reduction Is Gain,' summarizing the processes at the electrodes.

What ions are attracted to the positive terminal during electrolysis?

Bromide ions (Br-) are attracted to the positive terminal.

What is the process used to manufacture aluminium?

Electrolysis is the process used to manufacture aluminium.

What happens to bromide ions when they reach the anode?

Each bromide ion loses one electron to become a neutral bromine atom.

What is the purpose of adding cryolite to aluminium oxide during electrolysis?

Cryolite is added to lower the melting point of aluminium oxide, reducing energy costs.

What are the common materials used for inert electrodes in electrolysis?

Inert electrodes are often made from graphite or platinum.

What is the balanced equation for the reaction involving bromide ions?

2Br- → Br₂ + 2e-.

What is the formula to calculate concentration in a solution?

Concentration = number of moles ÷ volume.

What is the first step in the titration method?

Using a pipette, measure 25cm³ of sodium hydroxide solution and pour it into a conical flask.

What indicator is used in the titration method described?

Phenolphthalein is used as the indicator.

How do you determine the number of moles of sulfuric acid (H₂SO₄) in a titration?

Number of moles = concentration × volume.

What is the concentration of sodium hydroxide if 20cm³ of 1.0mol/dm³ sulfuric acid reacts with 25cm³ of sodium hydroxide?

The concentration of sodium hydroxide is 1.6mol/dm³.

What is the balanced symbol equation for the reaction between sodium hydroxide and sulfuric acid?

2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O.

What should you do if you go above the 0cm³ line when filling the burette?

Open the tap and allow the excess to run off into a beaker.

How do you convert cm³ to dm³?

To convert cm³ to dm³, divide by 1000.

What is the final step in the titration process?

Record the total volume of acid added to the sodium hydroxide.

What color change indicates the endpoint of the titration?

The indicator changes from pink to colourless.

How many times should the titration experiment be repeated for accuracy?

The experiment should be repeated twice more.

What is the significance of the indicator in a titration?

The indicator signals when the reaction has reached its endpoint by changing color.

What happens to the sodium hydroxide solution when sulfuric acid is added?

The sodium hydroxide solution is neutralized by the sulfuric acid.

What is the relationship between the number of moles of NaOH and H₂SO₄ in the reaction?

There is double the amount of NaOH compared to H₂SO₄.

What is the purpose of swirling the flask during titration?

Swirling the flask ensures thorough mixing of the reactants.

What is the final product formed when bromine atoms bond together?

The final product is the covalent molecule Br₂.