Chemical Changes

What are acids a source of in solution?

Hydrogen ions (H⁺).

What are alkalis a source of in solution?

Hydroxide ions (OH⁻).

What is the pH of a neutral solution?

pH 7.

What pH values do acidic solutions have?

Less than 7.

What pH values do alkaline solutions have?

Greater than 7.

What colour does blue litmus turn in an acid?

Red.

What colour does red litmus turn in an alkali?

Blue.

What colour is methyl orange in an acid?

Red.

What colour is methyl orange in an alkali?

Yellow.

What colour is phenolphthalein in an acid?

Colourless.

What colour is phenolphthalein in an alkali?

Pink.

How does hydrogen ion concentration affect the pH of an acidic solution?

The higher the hydrogen ion concentration, the lower the pH.

How does hydroxide ion concentration affect the pH of an alkaline solution?

The higher the hydroxide ion concentration, the higher the pH.

What happens to pH when hydrogen ion concentration increases by a factor of 10?

The pH decreases by 1.

What is the core practical investigating pH changes?

Investigate the change in pH when powdered calcium hydroxide or calcium oxide is added to a fixed volume of dilute hydrochloric acid.

What does dilute mean?

A solution containing a relatively small amount of dissolved substance compared with the amount of solvent.

What does concentrated mean?

A solution containing a relatively large amount of dissolved substance compared with the amount of solvent.

What is a strong acid?

An acid that completely dissociates into ions in solution.

What is a weak acid?

An acid that only partially dissociates into ions in solution.

What is a base?

A substance that reacts with an acid to form a salt and water only.

What is an alkali?

A soluble base.

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

Acid + metal → salt + hydrogen.

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

Acid + metal oxide → salt + water.

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

Acid + metal hydroxide → salt + water.

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

Acid + metal carbonate → salt + water + carbon dioxide.

How do you test for hydrogen gas?

Place a lit splint near the gas; hydrogen produces a squeaky pop.

How do you test for carbon dioxide?

Bubble the gas through limewater; the limewater turns milky/cloudy.

What is neutralisation?

A reaction between an acid and a base.

What happens in acid-alkali neutralisation?

Hydrogen ions from the acid react with hydroxide ions from the alkali to form water.

What is the ionic equation for acid-alkali neutralisation?

H⁺ + OH⁻ → H₂O.

Why is excess insoluble reactant added when preparing a soluble salt?

To ensure all of the acid reacts.

Why is the excess insoluble reactant removed when preparing a soluble salt?

It is insoluble, so it can be removed by filtration.

What remains in the solution after reacting an acid with an excess insoluble reactant?

Only the soluble salt and water.

Why must titration be used when preparing a soluble salt from an acid and a soluble reactant?

Because the soluble reactant cannot be separated from the solution by filtration.

What is done after finding the correct proportions in a titration?

The acid and soluble reactant are mixed in the correct proportions without the indicator.

What remains in the solution after correctly reacting an acid with a soluble reactant?

Only the salt and water.

What is the Topic 3 core practical for preparing copper sulfate?

Prepare pure, dry hydrated copper sulfate crystals starting from copper oxide, including using a water bath.

How is copper sulfate prepared from copper oxide?

Add excess copper oxide to warm sulfuric acid, filter off the excess copper oxide, then evaporate some water and cool the solution to crystallise copper sulfate.

Why is excess copper oxide added when preparing copper sulfate?

To ensure all the sulfuric acid is neutralised.

Why is a water bath used when preparing copper sulfate crystals?

To gently evaporate water and reduce the risk of overheating or splashing.

What equipment is used to carry out an acid-alkali titration?

A burette, pipette and suitable indicator.

What is a burette used for in a titration?

To accurately measure and deliver a variable volume of solution.

What is a pipette used for in a titration?

To accurately measure a fixed volume of solution.

Why is an indicator used in a titration?

To show when the acid and alkali have reacted in the correct proportions.

What is the solubility rule for sodium, potassium and ammonium salts?

All common sodium, potassium and ammonium salts are soluble.

What is the solubility rule for nitrates?

All nitrates are soluble.

What is the solubility rule for chlorides?

Common chlorides are soluble except silver chloride and lead chloride.

What is the solubility rule for sulfates?

Common sulfates are soluble except lead sulfate, barium sulfate and calcium sulfate.

What is the solubility rule for carbonates?

Common carbonates are insoluble except sodium, potassium and ammonium carbonates.

What is the solubility rule for hydroxides?

Common hydroxides are insoluble except sodium, potassium and ammonium hydroxides.

What is a precipitate?

An insoluble solid formed when two solutions react.

How can you predict whether a precipitate forms when two solutions are mixed?

Use the solubility rules to determine whether one of the possible products is insoluble.

How do you prepare a pure, dry insoluble salt?

Mix two suitable soluble solutions to form a precipitate, filter the precipitate, wash it with distilled water and dry it.

What is an electrolyte?

An ionic compound in the molten state or dissolved in water that conducts electricity.

What is electrolysis?

The decomposition of an electrolyte using electrical energy from a direct current supply.

What happens to positive ions during electrolysis?

Positive cations migrate to the negatively charged cathode.

What happens to negative ions during electrolysis?

Negative anions migrate to the positively charged anode.

What is the cathode?

The negative electrode in electrolysis.

What is the anode?

The positive electrode in electrolysis.

What is produced at the cathode during electrolysis?

Reduction occurs and a positive ion gains electrons.

What is produced at the anode during electrolysis?

Oxidation occurs and a negative ion loses electrons.

What happens during electrolysis of copper chloride solution using inert electrodes?

Copper is produced at the cathode and chlorine gas is produced at the anode.

What happens during electrolysis of sodium chloride solution using inert electrodes?

Hydrogen is produced at the cathode and chlorine is produced at the anode; sodium hydroxide remains in solution.

What happens during electrolysis of sodium sulfate solution using inert electrodes?

Hydrogen is produced at the cathode and oxygen is produced at the anode.

What happens during electrolysis of acidified water?

Hydrogen is produced at the cathode and oxygen is produced at the anode.

What happens during electrolysis of molten lead bromide?

Lead is produced at the cathode and bromine is produced at the anode.

How can you predict the products of electrolysis of a molten binary ionic compound?

The metal ion is reduced at the cathode to form the metal, while the non-metal ion is oxidised at the anode to form the non-metal.

What is a half equation?

An equation showing the electrons gained or lost by an ion during electrolysis.

What is the half equation for copper ion reduction?

Cu²⁺ + 2e⁻ → Cu.

What is the half equation for chloride ion oxidation?

2Cl⁻ → Cl₂ + 2e⁻.

What is oxidation in terms of electrons?

Loss of electrons.

What is reduction in terms of electrons?

Gain of electrons.

Where does reduction occur in electrolysis?

At the cathode.

Where does oxidation occur in electrolysis?

At the anode.

What happens during electrolysis of copper sulfate solution using copper electrodes?

Copper is deposited at the cathode and copper dissolves from the anode.

What happens to the mass of the cathode during copper sulfate electrolysis using copper electrodes?

It increases as copper is deposited.

What happens to the mass of the anode during copper sulfate electrolysis using copper electrodes?

It decreases as copper dissolves.

How can electrolysis be used to purify copper?

Impure copper is used as the anode, pure copper is the cathode, and copper ions move through the electrolyte and are deposited as pure copper at the cathode.

What is the Topic 3 core practical involving electrolysis?

Investigate the electrolysis of copper sulfate solution using inert electrodes and copper electrodes.