What ion is found in high concentration in a strong acid solution?
Hydrogen ions (H⁺).
What ion is found in high concentration in a strong alkali solution?
Hydroxide ions (OH⁻).
What ion is found in low concentration in a weak acid solution?
Hydrogen ions (H⁺).
What ion is found in low concentration in a weak alkali solution?
Hydroxide ions (OH⁻).
Give an example of a strong acid.
Hydrochloric acid (HCl), sulphuric acid (H₂SO₄), or nitric acid (HNO₃).
Give an example of a weak acid.
Ethanoic acid (CH₃COOH) or methanoic acid (HCOOH).
Give an example of a strong alkali.
Sodium hydroxide (NaOH), potassium hydroxide (KOH), or barium hydroxide (Ba(OH)₂).
Give an example of a weak alkali.
Aqueous ammonia (NH₃).
Do strong acids have a high or low pH?
Low pH.
Do strong alkalis have a high or low pH?
High pH.
Do weak acids have a higher or lower pH than strong acids?
Higher pH.
Do weak alkalis have a higher or lower pH than strong alkalis?
Lower pH.
What type of acid has the greatest effect on pH?
Strong acid.
What type of alkali has the greatest effect on pH?
Strong alkali.
Do strong acids or weak acids have a higher concentration of H⁺?
Strong acids.
Do strong alkalis or weak alkalis have a higher concentration of OH⁻?
Strong alkalis.
Explanation Questions
Explain how the degree of ionisation affects the strength of an acid.
The greater the degree of ionisation, the stronger the acid. Strong acids completely ionise and have high concentrations of H⁺ ions, while weak acids only partially ionise and have a lower concentration of H⁺ ions.
Explain how the degree of ionisation affects the strength of an alkali.
The greater the degree of ionisation, the stronger the alkali. Strong alkalis completely ionise and have high concentrations of OH⁻ ions, while weak alkalis only partially ionise and have a lower concentration of OH⁻ ions.
Why do strong acids have a lower pH than weak acids at the same concentration?
Strong acids completely ionise in water, producing a higher concentration of H⁺ ions compared to weak acids at the same concentration. The higher concentration of H⁺ ions results in a lower pH.
Why do strong alkalis have a higher pH than weak alkalis at the same concentration?
Strong alkalis completely ionise in water, producing a higher concentration of OH⁻ ions compared to weak alkalis at the same concentration. The higher concentration of OH⁻ ions results in a higher pH.
How does the concept of equilibrium relate to the ionisation of weak acids and alkalis?
Weak acids and alkalis do not fully ionise in water; instead, they reach an equilibrium between the unionised molecules and the ions they form. This means that the ionisation process is reversible, and only a proportion of the weak acid or alkali is in the ionised form.
How can the strength of an acid be identified experimentally, and how does this relate to its degree of ionisation?
The strength of an acid can be identified by measuring the pH of a solution. A strong acid will have a lower pH than a weak acid of the same concentration. This is because strong acids have a higher degree of ionisation and therefore, a higher H⁺ ion concentration.
How can the strength of an alkali be identified experimentally, and how does this relate to its degree of ionisation?
The strength of an alkali can be identified by measuring the pH of a solution. A strong alkali will have a higher pH than a weak alkali of the same concentration. This is because strong alkalis have a higher degree of ionisation and therefore, a higher OH⁻ ion concentration.
Give an example of a strong acid, and explain why it is classified as strong.
Hydrochloric acid (HCl) is a strong acid because it completely ionises in water to form a high concentration of H⁺ ions and chloride ions (Cl⁻).
Give an example of a weak alkali, and explain why it is classified as weak.
Aqueous ammonia (NH₃) is a weak alkali because it only partially ionises in water, resulting in a lower concentration of hydroxide (OH⁻) ions in solution, compared to a strong alkali.
Why is the degree of ionisation an important factor in determining the reactivity of an acid or alkali?
The degree of ionisation directly impacts the concentration of H⁺ or OH⁻ ions. A higher concentration of these ions leads to a higher reactivity, as these ions are the active species in acid/base reactions. Thus, strong acids and alkalis, due to their complete ionisation, are more reactive.