Acids + Bases

Question 1

State the definition of the pH scale

Answer 1

The pH scale is a numerical scale used to measure how acidic or alkaline a substance is. It ranges from 0 to 14.

Question 2

State the ions found in acids and alkalis

Answer 2

Acids contain a higher concentration of H+ ions than OH- ions
Alkalis contain a higher concentration of OH- ions than H+ ions
Neutral substances contain equal concentrations of OH- and H+ ions

Question 3

Recognise an acid and an alkali from compound names and formulas

Answer 3

Acids
The majority of acids end their name with the word “acid” such as hydrochloric acid and sulfuric acid. Common household acids are vinegar and citrus fruits.

Hydrochloric acid - HCl
Sulfuric acid - H2SO4
Nitric acid - HNO3

Bases
Bases neutralise acids. Soluble bases are alkalis.

Bases tend to be metal hydroxides, metal oxides or metal carbonates. Ammonia is a common alkali.

Potassium hydroxide - KOH
Sodium carbonate - Na2CO3
Ammonia - NH3

Question 4

State what happens to the pH when a solution is diluted

Answer 4

Acid
When an acid is diluted the pH increases (towards 7) as the concentration of H+ ions decreases.

Alkalis
When an alkali is diluted the pH decreases (towards 7) as the concentration of OH- ions decreases.

Question 5

State the pH of metal oxide and non-metal oxide solutions

Answer 5

Metal oxides and non-metal oxides can affect the pH of a solution differently when they dissolve in water:

Soluble metal oxides dissolve in water to form alkaline solutions (pH greater than 7)

Soluble non-metal oxides dissolve in water to form acidic solutions (pH less than 7)

Insoluble oxides do not dissolve in water and therefore have no effect on pH

Question 6

State the definition of a neutralisation reaction

Answer 6

A neutralisation reaction is when a base and an acid react together to form a neutral solution and salt.

Question 7

Write and recognise neutralisation equations

Answer 7

Metal oxide + acid → water + a salt

Metal hydroxide + acid → water + a salt

Metal carbonate + acid → water + a salt + carbon dioxide

Question 8

How can we name a salt from neutrilisation reaction

Answer 8

First Part
The first part comes from the metal in the base (e.g., hydroxide, carbonate)

Second Part
The second part of the name comes from the acid used

Example
Calcium hydroxide + sulfuric acid → calcium sulfate + water

Question 9

Explain what happens during a titration

Answer 9

A titration is an experimental method used to determine the concentration of an unknown solution.

Question 10

Describe the term spectator ion

Answer 10

A spectator ion is an ion which is present in a reaction but is not involved, it is only ‘observing’/’spectating’, and does not change state or charge.