HSC Chemistry: Applying Chemical Ideas Practice Questions

Question 1.

What is the best way to identify whether a solution contains barium ions or calcium ions? (1 mark)

A. Add chloride ions to the solution: barium will precipitate but calcium will not

B. Add carbonate ions to the solution: barium will precipitate but calcium will not

C. Do a flame test: barium produces a scarlet flame and calcium a blue/green flame

D. Do a flame test: barium produces a pale green flame and calcium a brick red flame

Question 2.

All the lead ions present in a 50.0 mL solution were precipitated by reaction with excess chloride ions. The mass of the dried precipitate was 0.595 g. What was the concentration of lead in the original solution? (1 mark)

A. 8.87 g/L

B. 10.2 g/L

C. 11.9 g/L

D. 16.0 g/L

Question 3.

The diagram shows the mass spectrum of an organic compound.

Which compound was analysed? (1 mark)

A. Butan-1-amine

B. Butanoic acid

C. Ethanoic acid

D. Iron(II) sulfide

Question 4.

A common antacid tablet contains aluminium hydroxide to neutralise stomach acid. In order for the antacid to be effective, each 500 mg tablet must contain a minimum of 200 mg of aluminium hydroxide.

Two antacid tablets were crushed and reacted with 70 mL of 0.60 mol L–1 hydrochloric acid. After the antacid had reacted with the acid, the remaining hydrochloric acid was titrated against 0.60 mol L–1 sodium hydroxide. The average volume of sodium hydroxide used was 35 mL.

Calculate the amount of aluminium hydroxide present in each tablet and justify whether the tablets will be effective as an antacid. (4 marks)

Question 5.

A bottle of solution is missing its label. It is either Pb(NO3) 2, Ba(NO3) 2 or Fe(NO3) 2.

Using only HCl, NaOH and H2SO4 solutions, outline a sequence of steps that could be followed to confirm the identity of the solution in the bottle. Include observed results and ionic equations in your answer. (4 marks)

Question 6.

Explain how infrared spectroscopy is used in the analysis and identification of organic substances. (3 marks)

Question 7.

The diagram is a schematic representation of a mass spectrometer.

(a) Name and outline the function of the part labelled A in the diagram. (2 marks)

(b) Outline the advantages of using mass spectrometry for analysis of a compound. (3 marks)

Question 8.

The following data were obtained for an organic compound containing carbon, hydrogen and oxygen. The compound is a colourless liquid that reacts with sodium carbonate powder to produce bubbles.

What is the structural formula of this compound? Justify your answer with reference to the information given on its reactivity and to at least THREE of the provided spectra. (5 marks)

Question 9.

Analyse the conditions required to optimise the production of ammonia using the Haber process. (7 marks)

Question 10. CHALLENGE!

An investigation was carried out using a series of precipitation reactions to determine the concentration of magnesium, silver, and copper ions present in a sample solution.

A 25.0 mL aliquot of the sample solution was pipetted into a conical flask. That solution was reacted with hydrochloric acid solution until no more precipitate was formed. The precipitate was extracted using gravity filtration, allowed to dry overnight and was found to have a mass of 1.36 g.

The filtrate was collected into a separate conical flask. That solution was treated with a dilute ammonia solution to neutralise the remaining hydrochloric acid. Sodium hydroxide solution was added to the resultant solution until no more precipitate was formed. A mixture of blue and white precipitates was obtained in the conical flask. The precipitates were filtered, dried in an oven, and recorded to have a mass of 2.40 g.

In a separate experiment, a fresh 20.0 mL aliquot of the sample solution was pipetted into a conical flask and titrated with a 0.427 mol L–1 solution of sodium carbonate. During this precipitation titration a series of coloured precipitates formed, starting with a pale, yellow silver precipitate, then a blue copper precipitate, followed by a white magnesium precipitate. The titre volume was recorded once a white precipitate had begun to form in the conical flask. The results of the precipitation titration are given in the table:

Calculate the concentrations of magnesium, silver, and copper ions in the original sample solution. Include a relevant chemical equation for each precipitation reaction. (6 marks)

Answers

Question 1. D

Question 2. A

Question 3. B

Question 4.

Number of moles of hydrochloric acid in 70ml:

n = cV = 0.60 x 0.070 = 0.042 moles.

35mL of the sodium hydroxide contains 0.60 x 0.035 = 0.021 moles. Thus 0.021 moles of hydrochloric acid remain. Therefore 0.021 moles must have reacted with the antacid in the tablets.

3HCl(aq) + Al(OH)3(aq) → AlCl2(s) + 3H2O(l)

As the mole ratio is 3:1, there must be 0.021/3 moles of aluminium hydroxide in 2 tablets = 0.007 x 78 = 0.546g thus each 500mg tablet would contain 273mg of aluminium hydroxide. The tablets are effective as 273mg is more than the required 200mg.

Question 5.

Question 6. Bonds between certain atoms in a molecule will absorb specific wavelengths of IR radiation depending on the length of the bond. Therefore, using the complete IR spectrum, the particular bonds in a molecule can be identified. The relative number of each specific bond can be determined by the degree of absorption. An organic substance will have a characteristic spectrum that can be used for its identification, by comparison with published data.

Question 7. (a) A is a magnet. It is required to separate/bend the stream of charged particles.

Question 7. (b) The mass spectrometer is able to quickly identify components of a mixture or components in a compound by their mass/charge ratio. Mass spectrometers cancan identify different isotopes of elements in a compound which allows the compound to be matched to a sample. Mass spectrometry is both qualitative and quantitative, requires only small quantities and is accurate, fast and sensitive.

Question 8.

Reaction with sodium carbonate implies that it is an organic acid as shown. The C NMR spectrum has three peaks; the peak at 180 ppm confirms the presence of a COOH group. The H NMR spectrum shows 3 separate proton environments – the splitting and integration indicate a CH3 group and a CH2 group. The mass spectrum has a parent ion at 74, indicating that the compound must have a molar mass of 74g/mol. Hence the compound is propanoic acid.

Question 9.

The Haber process is an industrial process used to manufacture ammonia according to the following equilibrium reaction.

N2(g) + 3H2(g) ⇌ 2NH3(g)
ΔH = –92 kJ/mol

To be economically viable it needs to produce a high yield at a reasonable rate. Increasing the temperature will provide the reactants with more energy and therefore increase the rate of reaction. According to Le Chatelier’s Principle (LCP) when a change is imposed on a system the system will adjust to minimise the change. Therefore if the temperature is increased the system will adjust to reduce the temperature by favouring the reverse, endothermic reaction and reducing the yield. As a result, the process is carried out at a moderate temperature of 450°C. An iron oxide catalyst is also added to increase the rate of reaction but this has no impact on the yield. According to LCP if the pressure is increased, the system will adjust to reduce the pressure by favouring the reaction that produces fewer moles of gas. In this process it will favour the production of ammonia, increasing the yield, but there is a limit to the pressure that the apparatus can safely withstand so it is carried out at pressures of about 300 atm. The equilibrium mixture is also passed through a condenser to remove the ammonia, shifting the equilibrium to favour the production of more ammonia and increasing the yield. To optimise the production of ammonia, it is important to monitor and maintain these conditions.

Question 10.

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