Chem Topic 3

What are acids in solution a source of?

Hydrogen ions, H⁺.

What are alkalis in solution a source of?

Hydroxide ions, OH⁻.

What is the pH of a neutral solution?

pH 7.

What pH do acidic solutions have?

Less than 7.

What pH do alkaline solutions have?

Greater than 7.

What happens to blue litmus in acid?

It turns red.

What happens to red litmus in alkali?

It turns blue.

What colour is methyl orange in acid?

Red.

What colour is methyl orange in alkali?

Yellow.

What colour is methyl orange at neutral pH?

Orange.

What colour is phenolphthalein in acid?

Colourless.

What colour is phenolphthalein in alkali?

Pink.

What happens to pH as hydrogen ion concentration increases?

pH decreases.

What happens to pH as hydroxide ion concentration increases?

pH increases.

What happens to pH when H⁺ concentration increases by a factor of 10?

pH decreases by 1.

What does the term dilute mean?

A small amount of solute compared with the amount of solvent.

What does the term concentrated mean?

A large amount of solute 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 the key difference between strong and weak acids?

The degree of dissociation into ions.

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 do acids react with metals to produce?

A salt and hydrogen.

What is the general equation for acid + metal?

Acid + metal → salt + hydrogen.

What do acids react with metal oxides to produce?

A salt and water.

What is the general equation for acid + metal oxide?

Acid + metal oxide → salt + water.

What do acids react with metal hydroxides to produce?

A salt and water.

What is the general equation for acid + metal hydroxide?

Acid + metal hydroxide → salt + water.

What do acids react with metal carbonates to produce?

A salt, water and carbon dioxide.

What is the general equation for acid + carbonate?

Acid + carbonate → salt + water + carbon dioxide.

How do you test for hydrogen gas?

Use a lit splint; hydrogen gives a squeaky pop.

How do you test for carbon dioxide?

Bubble it through limewater; the limewater turns cloudy.

What is neutralisation?

A reaction between an acid and a base.

What happens during acid-alkali neutralisation?

H⁺ ions react with OH⁻ ions to form water.

What is the ionic equation for neutralisation?

H⁺ + OH⁻ → H₂O.

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

To ensure all the acid reacts.

Why is excess insoluble reactant removed?

It is insoluble, so it can be filtered off.

What remains after reacting an acid with an excess insoluble reactant?

Only the soluble salt and water remain in solution.

Why is titration used with a soluble reactant?

You cannot filter off excess soluble reactant.

Why must soluble reactants be mixed in the correct proportions?

To ensure neither reactant is left in excess.

What remains after correct-proportion soluble reactants react?

Only the salt and water.

What is the purpose of a titration?

To find the exact volume needed for neutralisation.

Which apparatus delivers a measured volume in a titration?

A pipette.

Which apparatus measures the volume added during a titration?

A burette.

What is used to show when neutralisation is complete?

A suitable indicator.

How is pure dry hydrated copper sulfate prepared from copper oxide?

React copper oxide with excess sulfuric acid, filter, then crystallise.

Why is excess copper oxide used?

To ensure all the sulfuric acid reacts.

Why is excess copper oxide removed by filtration?

Copper oxide is insoluble.

Why is a water bath used when preparing crystals?

To gently evaporate water without overheating the crystals.

What is the formula of hydrated copper sulfate?

CuSO₄·5H₂O.

Which sodium salts are soluble?

All common sodium salts are soluble.

Which potassium salts are soluble?

All common potassium salts are soluble.

Which ammonium salts are soluble?

All common ammonium salts are soluble.

Are all nitrates soluble?

Yes, all nitrates are soluble.

Which common chlorides are insoluble?

Silver chloride and lead chloride.

Which common sulfates are insoluble?

Lead, barium and calcium sulfates.

Which common carbonates are soluble?

Sodium, potassium and ammonium carbonates.

Which common hydroxides are soluble?

Sodium, potassium and ammonium hydroxides.

What is a precipitate?

An insoluble solid formed when solutions are mixed.

How can you predict whether a precipitate forms?

Use the solubility rules.

How do you name an insoluble salt formed by precipitation?

Identify the positive ion and negative ion in the compound.

How do you prepare a pure dry insoluble salt?

Mix suitable solutions, filter the precipitate, wash it and dry it.

Why is the precipitate washed?

To remove soluble impurities.

Why is the precipitate dried?

To remove remaining water.

What is an electrolyte?

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

What is electrolysis?

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

What type of electrical supply is used in electrolysis?

Direct current (DC).

Which electrode attracts cations?

The negative cathode.

Which electrode attracts anions?

The positive anode.

What is the charge of a cation?

Positive.

What is the charge of an anion?

Negative.

Which way do cations move during electrolysis?

Towards the negative cathode.

Which way do anions move during electrolysis?

Towards the positive anode.

What happens at the cathode?

Reduction occurs.

What happens at the anode?

Oxidation occurs.

What is reduction in terms of electrons?

Gain of electrons.

What is oxidation in terms of electrons?

Loss of electrons.

What is a memory aid for oxidation?

OIL: Oxidation Is Loss of electrons.

What is a memory aid for reduction?

RIG: Reduction Is Gain of electrons.

What forms at the cathode during electrolysis?

A species gains electrons.

What forms at the anode during electrolysis?

A species loses electrons.

What are the products of copper chloride solution electrolysis?

Copper at the cathode and chlorine at the anode.

What happens to Cu²⁺ ions at the cathode?

Cu²⁺ + 2e⁻ → Cu.

What happens to chloride ions at the anode?

2Cl⁻ → Cl₂ + 2e⁻.

What are the products of sodium chloride solution electrolysis?

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

What happens at the cathode in sodium chloride solution?

Water gains electrons to form hydrogen and hydroxide ions.

What are the products of sodium sulfate solution electrolysis?

Hydrogen at the cathode and oxygen at the anode.

What happens at the cathode during electrolysis of acidified water?

Hydrogen is produced.

What happens at the anode during electrolysis of acidified water?

Oxygen is produced.

What are the products of molten lead bromide electrolysis?

Lead at the cathode and bromine at the anode.

What happens to Pb²⁺ in molten lead bromide?

Pb²⁺ + 2e⁻ → Pb.

What happens to Br⁻ in molten lead bromide?

2Br⁻ → Br₂ + 2e⁻.

How do you predict products of molten binary ionic compounds?

Cation forms the metal at the cathode; anion forms the non-metal at the anode.

Why must an ionic compound be molten or dissolved for electrolysis?

Its ions must be free to move.

What is a half equation?

An equation showing electron transfer at one electrode.

What is the cathode half equation for Cu²⁺?

Cu²⁺ + 2e⁻ → Cu.

What is the anode half equation for chloride ions?

2Cl⁻ → Cl₂ + 2e⁻.

What happens during electrolysis of copper sulfate using copper electrodes?

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

What happens to the copper anode?

Cu → Cu²⁺ + 2e⁻.

What happens to Cu²⁺ at the cathode?

Cu²⁺ + 2e⁻ → Cu.