Acids, bases and salts (C7.1-2)

What is produced when an acid reacts with a metal?

• Hydrogen gas and ammonia

• Water and carbon dioxide

• Salt and oxygen

• Salt and hydrogen gas

Answer explanation

When an acid reacts with a metal, it produces salt and hydrogen gas. The metal displaces hydrogen from the acid, resulting in the formation of a salt and the release of hydrogen gas, making 'Salt and hydrogen gas' the correct answer.

What is an alkali?

• A gas at room temperature

• A type of acid

• A water-soluble base

• A neutral substance

Answer explanation

An alkali is defined as a water-soluble base that can neutralize acids. This distinguishes it from gases, acids, and neutral substances, making 'A water-soluble base' the correct choice.

What color does litmus paper turn in acidic conditions?

• Green

• Yellow

• Blue

• Red

Answer explanation

Litmus paper turns red in acidic conditions. This is a key characteristic of litmus paper, which is used to test pH levels. In contrast, it turns blue in basic conditions.

What is an indicator?

• A solution that does not change color

• A base that neutralizes acids

• A type of acid

• A substance that changes color in acidic or alkaline conditions

Answer explanation

An indicator is a substance that changes color in response to acidic or alkaline conditions, helping to identify the pH level of a solution. The correct choice highlights this key property of indicators.

What is the general equation for the reaction of a metal carbonate with an acid?

• Acid + base ⟶ salt + carbon dioxide

• Base + acid ⟶ salt + water

• Metal + acid ⟶ salt + hydrogen gas

• Metal carbonate + acid ⟶ salt + carbon dioxide + water

Answer explanation

The correct equation for the reaction of a metal carbonate with an acid is: Metal carbonate + acid ⟶ salt + carbon dioxide + water. This reflects the typical products formed in such reactions.

What determines the identity of the salt produced in an acid-base neutralization reaction?

• The acid used and the positive ions in the base

• The temperature of the reaction

• The concentration of the acid

• The color of the acid

Answer explanation

The identity of the salt produced in an acid-base neutralization reaction is determined by the specific acid used and the positive ions from the base, as they combine to form the salt.

Which ions cause a substance to be acidic?

• Hydroxide ions

• Sodium ions

• Hydrogen ions

• Calcium ions

Answer explanation

Hydrogen ions (H+) are responsible for acidity in substances. The more H+ ions present, the more acidic the solution becomes, while hydroxide ions (OH-) contribute to basicity.

What pH is classed as neutral?

• 6

• 14

• 7

• 0

Answer explanation

A pH of 7 is considered neutral, meaning it is neither acidic nor basic. Values below 7 indicate acidity, while values above 7 indicate alkalinity.

What is the net ionic equation for neutralization?

• H+ (aq) + OH– (aq) ⟶ H2O (l)

• H+ (aq) + OH– (aq) ⟶ H2O (g)

• H2O (l) ⟶ H+ (aq) + OH– (aq)

• H+ (aq) + O2– (aq) ⟶ H2O (l)

Answer explanation

The correct net ionic equation for neutralization is H+ (aq) + OH– (aq) ⟶ H2O (l), which shows the reaction between hydrogen ions and hydroxide ions to form liquid water.

What is a proton donor?

• An acid that ionizes in solution

• A neutral substance

• A base that accepts protons

• A salt formed from an acid

Answer explanation

A proton donor is defined as an acid that ionizes in solution, releasing protons (H+ ions). This is why the correct answer is 'An acid that ionizes in solution', as it directly describes the behavior of acids.