Strong acids and alkalis completely dissociate into ions. So one mole of KOH or HCl gives one mole of H⁺ or OH⁻ ions.

pH can be found by pH = −log₁₀[H⁺] and pOH can be found by pOH = −log₁₀[OH⁻]

The relationship between [OH⁻] and [H⁺] is given by the ionic product of water (which should be learned):

K_w = [OH⁻] × [H⁺] = 1 × 10⁻¹⁴ (mol² dm⁻⁶) and therefore pH + pOH = 14 (at 298K).

Without a calculator it's important to rememeber that pH scale is logarithmic. E.g. 1.0 × 10⁻⁶ mol dm⁻³ HCl (aq) with have a pH of 6, and 1.0 × 10⁻⁵ mol dm⁻³ HCl (aq) will have a pH of 5 etc. (1.0 mol dm⁻³ HCl (aq) has a pH of 0)

1.0 × 10⁻⁶ mol dm⁻³ KOH (aq) will therefore have a pOH of 6, and a pH of 14-6 = 8.

1.0 × 10⁻⁶ mol dm⁻³ KOH (aq) is therefore the correct answer.

Incorrect answers

It is tempting to think that 1.0 × 10⁻⁸ mol dm⁻³ HCl (aq) will have a pH=8, but, at 298K a pH of 8 is alkaline, and HCl is an acid. In fact, we must remember that water also contributes H⁺ ions (1.0 × 10⁻⁷ mol dm⁻³ H⁺ ions). So the total H⁺ ion concentration of 1.0 × 10⁻⁸ mol dm⁻³ HCl (aq) at 298K will be 1.0 × 10⁻⁷ mol dm⁻³ from water and 1.0 × 10⁻⁸ mol dm⁻³ from HCl (aq). Giving a pH of a little under 7.

A Brønsted-Lowry base is an H⁺ ion (proton) acceptor. So in order to behave as a Brønsted-Lowry base, a species must have the capacity to accept an H⁺ ion. All the species given can accept an H+ ion (as they have an available lone pair and will form stable species) except the ammonium ion, which cannot.

Therefore NH₄⁺ is the correct answer.

Rain water is naturally acidic due to dissolved carbon dioxide, but this only causes mild acidity (pH ≈ 5.6).

Acid deposition occurs when oxides of nitrogen and sulfur dissolve in rain water.

Therefore 1 and 3 only is the correct answer.

Every acid has a conjugate base. To find the conjugate base of a Bronsted-Lowry acid, simply remove an H⁺ ion from the acid.

If we do that, we realise that three of the 'acids' given, that is CH₃COOH, C₂H₅COOH and NH₄⁺ are components of a weak acid/weak base equilibrium. (carboxylic acids are weak, and ammonia (NH₃) is weak.)

HNO₃ is a strong acid and fully dissociates into ions in solution, so NO₃⁻ will not accept an H⁺ ion easily, and is therefore the weakest conjugate base.

Therefore HNO₃ is the correct answer.

The Brønsted-Lowry model is our usual model for defining acids and bases.

A Brønsted-Lowry acid is a proton/hydrogen ion/H⁺ donor and a Brønsted-Lowry base is a proton/hydrogen ion/H⁺ acceptor. These definitions need to be learned. Thus the difference between a conjugate Brønsted-Lowry acid-base pair is a proton/hydrogen ion/H⁺.

Therefore A hydrogen ion is the correct answer.

An amphiprotic species can both accept or donate a proton (Therefore, is both a Brønsted-Lowry acid and a Brønsted-Lowry base).

(A Brønsted-Lowry acid is an H⁺ ion (proton) donor and a base is an H⁺ ion (proton) acceptor. So in order to behave as both, a species must be able to both donate and accept an H⁺ ion.)

Note that Al₂O₃ is amphoteric (can react as an acid or as a base) but is not amphiprotic (it has no H⁺ ions).

H₂PO₄⁻ can accept a proton to form H₃PO₄, or can donate a proton to form HPO₄²⁻. We should recognise that both these species (produced) are stable.

Therefore H₂PO₄⁻ is the correct answer.

pH can be found by pH = −log₁₀[H⁺] and pOH can be found by pOH = −log₁₀[OH⁻]

The relationship between [OH⁻] and [H⁺] is given by the ionic product of water (which should be learned):

K_w = [OH⁻] × [H⁺] = 1 × 10⁻¹⁴ (mol² dm⁻⁶) and therefore pH + pOH = 14 (at 298K).

Without a calculator it's important to rememeber that pH scale is logarithmic. E.g. 1.0 × 10⁻⁶ mol dm⁻³ H⁺ (aq) with have a pH of 6, and 1.0 × 10⁻⁵ mol dm⁻³ H⁺ (aq) will have a pH of 5 etc. (1.0 mol dm⁻³ H⁺ (aq) has a pH of 0)

A solution with [H+] = 1.0 × 10⁻¹² mol dm⁻³ will therefore have a pH of 12, which is basic. The other solutions are acidic.

[H+] = 1.0 × 10⁻¹² mol dm⁻³ is therefore the correct answer.

A Brønsted-Lowry acid is a proton/hydrogen ion/H⁺ donor. So the acid loses an H⁺ and gives it to something else.

The reaction is an equilibrium, and an H⁺ is transferred when the reaction takes place in both directions.

Left-to-right, the HCO₃⁻ is donating a proton to NH₃, and right-to-left the NH₄⁺ is donating a proton to CO₃²⁻.

Therefore the correct answer is: HCO₃⁻ and NH₄⁺

Strong acids and alkalis fully dissociate into ions in aqueous solution, weak acids and alkalis only partially dissociate.

Hydrochloric acid (HCl) and sulfuric acid (H₂SO₄) are strong acids, so fully dissociate into ions. H₂SO₄ dissociates into two moles of H⁺ ions (per mole of acid) and since pH = −log₁₀ [H⁺], H₂SO₄ will have a lower pH than HCl of the same concentration.

Ethanoic acid (CH₃COOH) is a weak acid, so will partially dissociate, and will therefore have a higher pH than any strong acid of equal concentration (HCl and H₂SO₄).

Sodium hydroxide is a strong alkali and will therefore have the highest pH.

Therefore NaOH > CH₃COOH > HCl > H₂SO₄ is the correct answer.

Acid reactions need to be learned:

Acid + Base (metal oxide/hydroxide) → Salt + Water

Acid + Metal → Salt + Hydrogen

Acid + Metal Carbonate (or Metal Hydrogen Carbonate) → Salt + Water + Carbon Dioxide

And neutralising: hydrochloric acid produced chlorides; sulfuric acid produces sulfates; nitric acid produces nitrates.

The formula of calcium nitrate is Ca(NO₃)₂ since calcium is in group 2 (Ca²⁺) and the nitrate ion has a formula of NO₃⁻ (compound ions must be learned).

Therefore Ca(NO₃)₂ + H₂O + CO₂ is the correct answer.

Every base has a conjugate acid. (To find the conjugate acid of a Bronsted-Lowry base, simply add an H⁺ ion to the base.)

We need to remember that strong bases are good proton acceptors (and they fully dissociate into ions in aqueous solution) so the conjugate acid of a strong base will be a weak acid, since it will not easily give up a proton/hydrogen ion (and return to the strong base).

Therefore A strong base is a good proton acceptor and has a weak conjugate acid is the correct answer.

pH can be found by pH = −log₁₀[H⁺]

Without a calculator it's important to rememeber that pH scale is logarithmic. E.g. 1.0 × 10⁻⁶ mol dm⁻³ HCl (aq) with have a pH of 6, and 1.0 × 10⁻⁵ mol dm⁻³ HCl (aq) will have a pH of 5 etc. (1.0 mol dm⁻³ HCl (aq) has a pH of 0)

And therefore diluting the [H⁺] by 10 will increase the ph by 1, diluting by 100 will increase by 2, diluting by 1000 will increase by 3 etc. (diluting an acid increases pH).

In this question, the [HCl] (and therefore [H⁺]) is diluted by 100 times (10cm³ to 1000cm³ total), thus the pH will increase by 2.

pH = 5 is therefore the correct answer.