Chemistry - CHEMICAL CHANGES (C4)

Acids, Bases, & Alkalis -

What is an acid?

A substance that forms H+ ions in aqueous solution.

Acids, Bases, & Alkalis -

What is an alkali?

A base that dissolves in water to form OH- ions.

Acids, Bases, & Alkalis -

What is a base?

A substance that reacts w/ an acid to form a salt + water.

Acids, Bases, & Alkalis -

What is the pH scale?

A scale from 0-14 showing how acidic / alkaline a solution is (0= very acidic, 14= very alkaline).

Acids, Bases, & Alkalis -

What does a universal indicator show?

The pH of a solution by changing colour.

Acids, Bases, & Alkalis -

What is the ionic equation for neutralisation?

H⁺ + OH⁻ → H₂O

Strong & Weak Acids -

What is a strong acid?

An acid that completely ionises in water.

Strong & Weak Acids -

What is a weak acid?

An acid that only partially ionises in water (e.g. ethanoic acid).

Strong & Weak Acids -

Does a strong acid always have a low pH?

Yes, because it produces a high concentration of H+ ions.

Strong & Weak Acids -

How does concentration differ from strength?

Strength is how much the acid ionises; concentration is how many acid particles - in a given volume.

Reactions of Acids -

What is the general word equation for acid + metal?

Acid + Metal → Salt + Hydrogen

Reactions of Acids -

What is the test for hydrogen gas?

A lit splint gives a ‘squeaky pop’ in the presence of hydrogen.

Reactions of Acids -

What is the general word equation for acid + base/alkali?

Acid + Base → Salt + Water

Reactions of Acids -

What is the general word equation for acid + metal carbonate?

Acid + Metal Carbonate → Salt + Water + Carbon Dioxide

Reactions of Acids -

What’s the test for carbon dioxide?

Turns limewater cloudy.

Making Salts -

How do you make a soluble salt from an insoluble base?

Add base to warm acid until no more reacts (excess), filter, then crystallise the solution.

Making Salts -

What method is used to make pure, dry crystals of a salt?

Crystallisation (heat solution gently + allow it to cool).

Reactivity Series -

What is the reactivity series?

A list of metals ordered by how easily they lose electrons (reactivity w/ water/acid).

Reactivity Series -

Name the first 5 elements in the reactivity series.

Potassium, Sodium, Calcium, Magnesium, Aluminium.

Reactivity Series -

How do metals above hydrogen in the reactivity series react w/ acids?

They react to produce hydrogen gas.

Reactivity Series -

What is a displacement reaction?

A more reactive metal displaces a less reactive metal from its compound.

Extracting Metals -

How are metals less reactive than carbon extracted?

By reduction w/ carbon (e.g. iron from iron oxide).

Extracting Metals -

How are metals more reactive than carbon extracted?

By electrolysis.

Extracting Metals -

What is reduction?

Gain of electrons / loss of oxyegn.

Extracting Metals -

What is oxidation?

Loss of electrons / gain of oxygen.

Electrolysis -

What is electrolysis?

The decomposition of a compound using electricity.

Electrolysis -

What is an electrolyte?

An ionic substance that’s molten / dissolved in water to conduct electricity.

Electrolysis -

What happens at the cathode (-) during electrolysis?

Positive ions gain electrons (reduction).

Electrolysis -

What happens at the anode (+) during electrolysis?

Negative ions lose electrons (oxidation).

Electrolysis -

What is produced at the cathode if hydrogen ions + metal ions are present?

Hydrogen is produced if the metal is more reactive than hydrogen.

Electrolysis -

What is produced at the anode in electrolysis of aqueous solutions?

Oxygen - usually produced unless halide ions (Cl-, Br-, I-) are present.