Acids and bases: Grade 11 Past Paper Questions

QUESTION 4. The balanced equation below represents the ionisation of nitric acid (HNO₃) in water: HNO₃(l) + H₂O(l) ⇌ H₃O⁺(aq) + NO₃⁻(aq). 4.1.1 Define an acid in terms of the Lowry-Brønsted theory. 4.1.2 Write down the FORMULAE of the TWO bases in the equation above. 4.1.3 Is nitric acid a STRONG or a WEAK acid? Give a reason for the answer. 4.1.4 Define an ampholyte. 4.1.5 Write down the formula of an ampholyte present in the equation above. 4.2 A learner performs a titration using a standard potassium hydroxide solution of concentration 0,1 mol·dm⁻³ and sulphuric acid of unknown concentration. The balanced equation for the reaction is: H₂SO₄(aq) + 2KOH(aq) → K₂SO₄(aq) + 2H₂O(l). 4.2.1 Define a standard solution. The titration is done three times (Runs 1, 2 and 3) using the same indicator. The volumes of the acid and base solutions used for each run are indicated in a table, recording 25 cm³ of KOH against 20,90 cm³ and 21,24 cm³ of H₂SO₄ for two of the titration runs. 4.2.2 Using the above data, determine the concentration of the H₂SO₄ solution. 4.2.3 The following is a list of possible indicators that can be used: methyl orange (3,1–4,4), bromothymol blue (6–8), phenolphthalein (8–10). Which indicator is most suitable for this titration? Give a reason for the answer.

1.4 Which ONE of the following pairs represents the CONJUGATE ACID and CONJUGATE BASE of HPO₄²⁻? A. PO₄³⁻ and HPO₄²⁻ B. HPO₄²⁻ and H₃PO₄ C. H₂PO₄⁻ and PO₄³⁻ D. HPO₄²⁻ and PO₄³⁻. 1.5 Which ONE of the following processes is exothermic? A. Melting ice cubes. B. Baking bread. C. Burning a candle. D. Photosynthesis. 1.6 Which ONE of the following is correct for Boyle's Law? A. P ∝ 1/V when temperature is constant. B. P ∝ V when temperature is constant. C. P ∝ 1/T when volume is constant. D. P ∝ T when volume is constant. 1.7 Which ONE of the following graphs represents the deviation of real gas behaviour (broken line) from ideal gas behaviour (solid line)?

4.3 A solution is formed by adding 30 cm³ of HCl of concentration 0,15 mol·dm⁻³ to 20 cm³ of Ca(OH)₂ of concentration 0,1 mol·dm⁻³, according to the following balanced equation: Ca(OH)₂ + 2HCl → CaCl₂ + 2H₂O. Determine the final pH of the solution. QUESTION 5. 5.1 A gas is contained in Chamber A, which has a volume of 5,3 dm³, and is sealed off from Chamber B, which has a volume of 3,2 dm³. Initially, only Chamber A contains gas at a pressure of 135,2 kPa, while Chamber B is a vacuum (contains no gas). The chambers are then connected by opening a valve between them, and the gas is allowed to expand freely. The temperature remains constant and no gas escapes. 5.1.1 State Boyle's Law in words. 5.1.2 Explain, in terms of Boyle's Law, what happens to the pressure of the gas after the valve is opened. 5.1.3 Calculate the final pressure of the gas after the valve is opened. 5.2 Sketch a graph that shows the relationship between pressure (y-axis) and volume (x-axis) for a fixed amount of gas at constant temperature. 5.3 State the conditions of temperature and pressure under which a real gas behaves as an ideal gas. 5.4 Which real gas behaves the closest to an ideal gas? Explain the answer.

3.6 Redraw the above graph in your answer book, and label it A. Do not label the axes or show any given values. On the same set of axes, draw the graph that will be obtained if a catalyst is added. Label this as graph B. QUESTION 4. The balanced equation below represents the ionisation of nitric acid (HNO₃) in water: HNO₃(l) + H₂O(l) ⇌ H₃O⁺(aq) + NO₃⁻(aq). 4.1.1 Define an acid in terms of the Lowry-Brønsted theory. 4.1.2 Write down the FORMULAE of the TWO bases in the equation above. 4.1.3 Is nitric acid a STRONG or a WEAK acid? Give a reason for the answer. 4.1.4 Define an ampholyte. 4.1.5 Write down the formula of an ampholyte present in the equation above. 4.2 A learner performs a titration using a standard potassium hydroxide solution of concentration 0,1 mol·dm⁻³ and sulphuric acid of unknown concentration. The balanced equation for the reaction is: H₂SO₄(aq) + 2KOH(aq) → K₂SO₄(aq) + 2H₂O(l). 4.2.1 Define a standard solution. 4.2.2 Using the above data, determine the concentration of the H₂SO₄ solution.