7 1 the characteristic properties of acids and bases

When an acid reacts with a metal, it produces a salt and hydrogen gas.

An alkali is a water-soluble base.

In acidic conditions, litmus paper turns red.

True. Thymolphthalein turns blue in alkaline conditions.

Litmus is not suitable for titrations because its color change is not sharp and it goes through a purple transition color in neutral solutions.

An indicator is a substance that changes colour in acidic or alkaline conditions, used to determine the pH of a solution.

A neutralisation reaction is a reaction between an acid and a base to form a salt and water.

False. Effervescence is produced when an acid reacts with a metal carbonate, due to the formation of carbon dioxide gas.

The products formed from the reaction between sodium hydroxide and hydrochloric acid are sodium chloride and water.

The general equation for the reaction of a metal carbonate with an acid is: metal carbonate + acid ⟶ salt + carbon dioxide + water

The word equation for the reaction between sodium carbonate and sulfuric acid is: sodium carbonate + sulfuric acid ⟶ sodium sulfate + water + carbon dioxide

The identity of the salt produced depends on the acid used and the positive ions in the base.

Metal oxides, metal hydroxides and metal carbonates act as bases in acid-base reactions.

The ion that causes a substance to be acidic is a hydrogen ion / H+.

The ion that causes a substance to be alkaline is a hydroxide ion / OH-.

pH 7 is classed as neutral.

The pH range for alkaline is 8-14.

The pH range for an acid is 0-6.

True. The higher the concentration of hydrogen ions, the lower the pH.

True. The higher the concentration of hydroxide ions in solution, the higher the pH.

The net ionic equation for neutralisation is: H+  (aq) + OH– (aq)⟶ H2O (l)

The pH of distilled water is 7.

To measure the pH of a substance with universal indicator: (Universal indicator paper can also be used).

A proton donor is an acid that ionises in solution producing protons (H+ ions).

A proton acceptor is a base that accepts protons donated by an acid.

A strong acid is an acid that completely dissociates (or ionises) in water, producing solutions of a very low pH.

A weak acid is an acid that partially dissociates (or ionises) in water, producing pH values closer to the middle of the pH scale, while still being below 7.

True. HCl is an example of a strong acid.

The equation for the dissociation of HCl in water is: HCl (aq) → H+ (aq) + Cl- (aq)

True. Weak acids form an equilibrium in water between molecules and their ions.

An example of a weak acid is propanoic acid (CH3CH2COOH). Carboxylic acids are good examples of weak acids.

A concentrated solution is a solution that contains a higher number of solute molecules per dm3 of solution.

False. A concentrated acid solution is not always stronger than a dilute acid solution. It depends on the degree of dissociation.

An oxide is a compound made from one or more atoms of oxygen combined with one other element.

An acidic oxide is an oxide formed when a non-metal element combines with oxygen, reacting with bases to form a salt and water.

A basic oxide is an oxide formed when a metal element combines with oxygen, reacting with acids to form a salt and water.

True. CO2 is an example of an acidic oxide.

True. CuO is an example of a basic oxide.

Acidic oxides produce an acidic solution with a low pH when dissolved in water.

Basic oxides produce a basic solution with a high pH when dissolved in water.

An amphoteric oxide is an oxide that can behave as both acidic and basic, depending on whether the other reactant is an acid or a base.

Two examples of amphoteric oxides are zinc oxide (ZnO) and aluminium oxide (Al2O3).

False. Amphoteric oxides react with both acids and bases.