Unit 1-Acids & Bases Topic 7

Question 1

1. What does the pH of a substance tell you?
2. What range of numbers does the pH scale span?

Answer 1

1. How acidic or alkaline a substance is (the pH of the substance)
2. pH scale is continuous range that stretches from below 0 to above 14.

Most common pH values occur between 0 and 14.

Question 2

What word is used to describe chemical with a pH of

a. Less than 7
b. exactly 7
c. More than 7

Answer 2

a. Acids have a pH of less than 7.
b. Water and neutral solutions have a pH of exactly 7.
c. Alkalis have a pH more than 7.

Question 3

What is the difference between a base and an alkali?

Answer 3

Substances that can react with acids and neutralise them to make a salt and water are called bases.

Bases that dissolve in water are called alkalis.

Question 4

How are acids and alkalis formed?

Answer 4

An alkaline solution can be formed when a metal oxide is dissolved in water.

An acidic solution can be formed when a non-metal oxide is dissolved in water.

Question 5

The data booklet has a table of solubilities on page 8. What type of chemicals would have no effect on pH?

Answer 5

Insoluble substances will have no effect on pH.

Question 6

Acidic and alkaline solutions can conduct electricity because they have ions that are free to carry charge.

What ion do all acids contain?

Answer 6

Hydrogen ion

H⁺

Question 7

Which acids are the following formulae representing?

i) HCl or H⁺ _(aq)Cl^-_(aq)
ii) H₂SO₄ or 2H⁺_(aq) SO₄^2-_(aq)
iii) HNO₃ or H⁺_(aq) NO₃^{<span>-</span>}(aq)

Answer 7

i) Hydrochloric acid
ii) Sulphuric acid
iii) Nitric acid

Question 8

Acidic and alkaline solutions can conduct electricity because they have ions that are free to carry charge.

What ion do all alkalis contain?

Answer 8

Hydroxide ion

OH^{<span>-</span>}

Question 9

Which alkalis are the following formulae representing?

i) NaOH or Na⁺ _(aq) OH^-_(aq)
ii) Ca(OH)₂ or Ca⁺_(aq) 2OH^-_(aq)
iii) LiOH or Li⁺_(aq) OH^-(aq)

Answer 9

i) Sodium hydroxide
ii) Calcium hydroxide
iii) Lithium hydroxide

Question 10

Describe how the concentration of H⁺ ions and pH changes when an acid is diluted.

Answer 10

When an acid is diluted the concentration of H+ ions is decreased and the pH increases towards 7.

Question 11

Describe how the concentration of OH^- ions and pH changes when an alkali is diluted.

Answer 11

When an alkali is diluted the concentration of OH- ions is decreased and the pH decreases towards 7.

Question 12

Water is a covalent compound. These do not conduct electricity.

Yet I was always told not to make toast in the bath.

Please explain.

Answer 12

No one likes soggy toast.

A very small proportion of water molecules will dissociate into an equal number of hydrogen and hydroxide ions.

H₂O_(l) ⇔ H⁺_(aq) + OH^-_(aq)

Question 13

How does the concentration of hydrogen ions (H⁺_(aq)) compare to the concentration of hydroxide ions (OH^-_(aq)) in water and neutral solutions?

Answer 13

In water and neutral solutions, the concentration of hydrogen ions (H⁺_(aq)) is equal to the concentration of hydroxide ions (OH^-_(aq)) .

Question 14

How does the concentration of hydrogen ions (H⁺_(aq)) compare to the concentration of hydroxide ions (OH^-_(aq)) in an alkaline solution,

Answer 14

In alkaline solutions, the concentration of hydroxide ions (OH^-(aq) is greater than the hydrogen ion (H⁺(aq)) concentration.

Question 15

How does the concentration of hydrogen ions (H⁺_(aq)) compare to the concentration of hydroxide ions (OH^-_(aq)) in an acidic solution.

Answer 15

In acidic solutions, the concentration of hydrogen ions (H⁺_(aq)) is greater than the hydroxide ion (OH^-_(aq)) concentration.