C5.8 - Strong and weak acids

Question 1

Some acids are what than others?

Answer 1

Some acids are safer to use than others

Question 2

What the strong acid enough and it will eventually do what?

Answer 2

Dilute the strong acid enough and it will eventually become harmless

Question 3

Dilute the strong acid enough and it will eventually become harmless.
Example

Answer 3

For example, a solution of 6.0 mol/dm³ HCl is relatively concentrated and would have to be labelled as corrosive

Question 4

Some acids, such as the weak acid citric acid, are not harmful when in what?

Answer 4

Some acids, such as the weak acid citric acid, are not harmful when in:
1. Dilute
Or,
2. Even concentrated solutions

Question 5

Examples of strong acids

Answer 5

Examples of strong acids are:

1. Hydrochloric acid
2. Nitric acid
3. Sulfuric acid

Question 6

Examples of weak acids

Answer 6

Examples of weak acids are:

1. Citric acid
2. Ethanoic acid
3. Carbonic acid

Question 7

When is carbon dioxide gas, CO2, given off more slowly?

Answer 7

Carbon dioxide gas, CO2, is given off more slowly, when a metal carbonate reacts with a carboxylic acid (ethanoic acid), as compared with hydrochloric acid of the same concentration

Question 8

What are carboxylic acids called?

Answer 8

Carboxylic acids are called weak acids

Question 9

Weak acids

Answer 9

Weak acids are acids that do not ionise completely in aqueous solutions

Question 10

Strong acids

Answer 10

Strong acids are acids that completely ionise in aqueous solutions

Question 11

What is the pH of a 0.1 mol/dm³ solution of HCl (a strong acid)?

Answer 11

The pH of a 0.1 mol/dm³ solution of HCl (a strong acid) is 1.0

Question 12

The pH of a 0.1 mol/dm³ solution of HCl (a strong acid is 1.0.
Yet, what pH does a 0.1 mol/dm³ solution of ethanoic acid (a weak acid) have?

Answer 12

A 0.1 mol/dm³ solution of ethanoic acid (a weak acid) has a pH of only 2.9

Question 13

The pH of a 0.1 mol/dm³ solution of HCl (a strong acid is 1.0.
Yet, a 0.1 mol/dm³ solution of ethanoic acid (a weak acid) has a pH of only 2.9.
What does this mean?

Answer 13

This means that the solution of ethanoic acid is not as acidic, even though the 2 solutions have the same concentration

Question 14

What must acids do before they show their acidic properties?

Answer 14

Acids must dissolve in water before they show their acidic properties

Question 15

Why must acids dissolve in water before they show their acidic properties

Answer 15

Acids must dissolve in water before they show their acidic properties, because in water all acids ionise (split up)

Question 16

Acids must dissolve in water before they show their acidic properties, because in water all acids ionise (split up).
What do their molecules do?

Answer 16

Their molecules split up to form:

1. H+ (aq) ions
2. Negative ions

Question 17

Acids must dissolve in water before they show their acidic properties, because in water all acids ionise (split up).
Their molecules split up to form H+ (aq) ions and negative ions.
What do all acidic solutions have in common?

Answer 17

All acidic solutions have H+ (aq) ions in common

Question 18

What do strong acids do in solution?

Answer 18

Strong acids ionise completely in solution

Question 19

Strong acids ionise completely in solution.

However, what happens in weak acids?

Answer 19

In weak acids, most of the molecules:

1. Stay as they are
2. Do not release H+ ions into the solution

Question 20

In weak acids, most of the molecules stay as they are - they do not release H+ ions into the solution
Only a relatively small proportion of the acidic molecules will ionise in their solutions.
What is the reaction?

Answer 20

The reaction is reversible

Question 21

The reaction of the ionisation of a strong acid is what?

Answer 21

The reaction of the ionisation of a strong acid is irreversible

Question 22

In weak acids, most of the molecules stay as they are - they do not release H+ ions into the solution
Only a relatively small proportion of the acidic molecules will ionise in their solutions.
The reaction is reversible, unlike the ionisation of a strong acid.
So what happens as the molecules of the weak acid split up to form H+ ions and negative ions?

Answer 22

As the molecules of the weak acid split up to form:
1. H+ ions
2. Negative ions
,the ions recombine to form the original molecules again

Question 23

Equilibrium

Answer 23

Equilibrium is the point in a reversible reaction at which the:
1. Forward
2. Backward
rates of reaction are the same

Question 24

Given 2 aqueous solutions of equal concentration, what will the strong acid have?

Answer 24

Given 2 aqueous solutions of equal concentration, the strong acid will have a higher concentration of H+ (aq) ions than the solution of the weak acid

Question 25

Given 2 aqueous solutions of equal concentration, the strong acid will have a higher concentration of H+ (aq) ions than the solution of the weak acid. So, what does a weak acid have?

Answer 25

A weak acid has a higher pH value

Question 26

What happens because a weak acid has a higher pH value?

Answer 26

Because a weak acid has a higher pH value, it reacts more slowly than a strong acid with a metal carbonate

Question 27

The pH of a 0.10 mol/dm³ solution of dilute hydrochloric acid is 1.0. In this solution of hydrochloric acid, why is the concentration of hydrogen ions, H+ (aq), also 0.10 mol/dm³?

Answer 27

The concentration of hydrogen ions, H+ (aq), is also 0.10 mol/dm³, because HCl (aq) ionises completely in solution

Question 28

The pH value when the concentration of H+ (aq) ions is 0.10 mol/dm³

Answer 28

The pH value when the concentration of H+ (aq) ions is 0.10 mol/dm³ is 1.0

Question 29

The pH value when the concentration of H+ (aq) ions is 0.010 mol/dm³

Answer 29

The pH value when the concentration of H+ (aq) ions is 0.010 mol/dm³ is 2.0

Question 30

The pH value when the concentration of H+ (aq) ions is 0.0010 mol/dm³

Answer 30

The pH value when the concentration of H+ (aq) ions is 0.0010 mol/dm³ is 3.0

Question 31

The pH value when the concentration of H+ (aq) ions is 0.00010 mol/dm³

Answer 31

The pH value when the concentration of H+ (aq) ions is 0.00010 mol/dm³ is 4.0

Question 32

What happens as the concentration of hydrogen ions, H+ (aq), decreases by a factor of 10 (an order of magnitude)?

Answer 32

As the concentration of hydrogen ions, H+ (aq), decreases by a factor of 10 (an order of magnitude), the pH value increases by 1 unit

Question 33

0.10 in standard form

Answer 33

0.10 in standard form is 1.0 x 10 to the power of -1

Question 34

0.010 in standard form

Answer 34

0.010 in standard form is 1.0 x 10 to the power of -2

Question 35

0.0010 in standard form

Answer 35

0.0010 in standard form is 1.0 x 10 to the power of -3

Question 36

0.00010 in standard form

Answer 36

0.00010 in standard form is 1.0 x 10 to the power of -4

Question 37

Dilute the strong acid enough and it will eventually become harmless. For example, a solution of 6.0 mol/dm³ HCl is relatively concentrated and would have to be labelled as corrosive. However, when that solution is diluted by adding water to give a solution of 0.10 mol/dm³ HCl, it what?

Answer 37

When that solution is diluted by adding water to give a solution of 0.10 mol/dm³ HCl, it only requires labelling as irritant

Question 38

Examples of weak acids are citric acid, ethanoic acid and carbonic acid. Citric acid is found in what?

Answer 38

Citric acid is found in citrus fruits

Question 39

Examples of weak acids are citric acid, ethanoic acid and carbonic acid. Ethanoic acid is found in what?

Answer 39

Ethanoic acid is found in vinegar

Question 40

Examples of weak acids are citric acid, ethanoic acid and carbonic acid. Carbonic acid is found in what?

Answer 40

Carbonic acid is found in: 1. Rainwater 2. Fizzy drinks

Question 41

Carboxylic acids are called weak acids, as opposed to strong acids such as what?

Answer 41

Carboxylic acids are called weak acids, as opposed to strong acids such as hydrochloric acid

Question 42

Strong acids ionise completely in solution. In weak acids, most of the molecules stay as they are and do not release H+ ions into the solution. Only a relatively small proportion of the acidic molecules will do what?

Answer 42

Only a relatively small proportion of the acidic molecules will ionise in their solutions

Question 43

In weak acids, most of the molecules stay as they are - they do not release H+ ions into the solution Only a relatively small proportion of the acidic molecules will ionise in their solutions. The reaction is reversible, unlike what?

Answer 43

The reaction is reversible, unlike the ionisation of a strong acid

Question 44

In weak acids, most of the molecules stay as they are - they do not release H+ ions into the solution Only a relatively small proportion of the acidic molecules will ionise in their solutions. The reaction is reversible, unlike the ionisation of a strong acid. As the molecules of the weak acid split up to form H+ ions and negative ions, the ions recombine to form the original molecules again. A position of equilibrium is reached in which what?

Answer 44

A position of equilibrium is reached in which both: 1. Whole molecules (the majority) 2. Their ions (the minority) are present

Question 45

Equilibrium is the point in a reversible reaction at which the forward and backward rates of reaction are the same. Therefore, the amounts of substances present in the reacting mixture do what?

Answer 45

Therefore, the amounts of substances present in the reacting mixture remain constant