Paper 3: Practical skills, all content and multiple choice

Describe how to make 250 cm³ of a standard solution of sodium carbonate from a weighed solid.

Titres (cm³) for a hydrochloric acid solution against 25.0 cm³ of sodium carbonate standard solution: 22.45, 22.60, 22.40, 22.50. Identify the concordant titres and calculate the mean titre.

Each burette reading has an uncertainty of ±0.05 cm³. Calculate the percentage uncertainty in a titre of 22.45 cm³.

Explain why the burette should be rinsed with the acid before filling.

In an iodine clock reaction, explain how the time for the blue-black colour to appear is used to measure the initial rate.

Results (data are illustrative, written for this paper):

[H₂O₂] / mol dm⁻³	0.020	0.040	0.060	0.080
Time / s	120	60	41	30

Calculate 1/t for each and deduce the order with respect to H₂O₂.

Give two variables that must be kept constant.

Describe how to set up a cell to measure the EMF between a copper electrode in Cu²⁺(aq) and a zinc electrode in Zn²⁺(aq).

Explain why potassium nitrate is used in the salt bridge rather than potassium chloride.

The measured EMF was 1.04 V instead of 1.10 V. Suggest two reasons.

Cyclohexene was prepared by heating cyclohexanol with phosphoric acid and distilling. Describe how to purify the impure distillate.

5.00 g of cyclohexanol (Mr 100.0) gave 2.87 g of cyclohexene (Mr 82.0). Calculate the percentage yield.

Describe a test to confirm that the product contains an alkene.

Give two reasons for adding anti-bumping granules and heating gently.

Explain why the baseline on a TLC plate is drawn in pencil and why it is above the solvent level.

Amino acids are colourless. Describe how their spots can be located.

For the Haber process, N₂ + 3H₂ ⇌ 2NH₃, ΔH = −92 kJ mol⁻¹. Explain why the industrial conditions are 450 °C and 200 atm with an iron catalyst, referring to yield, rate and cost.

Ethanoic acid is titrated with sodium hydroxide. Explain the shape of the pH curve and choose a suitable indicator from methyl orange (pH 3.1–4.4) and phenolphthalein (pH 8.3–10.0).

25.0 cm³ of a solution of iron(II) ions required 18.20 cm³ of 0.0200 mol dm⁻³ acidified KMnO₄ for complete reaction. Calculate the concentration of Fe²⁺ and explain why no indicator is needed.

Compound X, C₃H₆O₂, reacts with sodium carbonate to produce CO₂. Its ¹H NMR spectrum has three peaks: a triplet (3H), a quartet (2H) and a singlet (1H) at δ 11.0. Identify X and explain your reasoning.

Which species has the same electron configuration as Ar?

How many molecules are in 0.500 mol of water?

Which molecule has a bond angle of 104.5°?

Which substance has a giant covalent structure?

Standard enthalpy of formation is defined for 1 mol of a compound formed from its elements under standard conditions. Which has ΔfH° = 0?

Which change increases the rate of a reaction of a solid with acid without changing the activation energy?

For an exothermic equilibrium, increasing temperature will

What is the oxidation state of sulfur in Na₂S₂O₃?

Which process has a negative entropy change?

The units of a first-order rate constant are

For a gas mixture at total pressure 300 kPa containing 2 mol A and 1 mol B, the partial pressure of A is

Which is the strongest oxidising agent? (E°: Cl₂/Cl⁻ +1.36, Br₂/Br⁻ +1.09, I₂/I⁻ +0.54, Fe³⁺/Fe²⁺ +0.77 V)

What is the pH of 0.010 mol dm⁻³ NaOH at 298 K? (Kw = 1.0 × 10⁻¹⁴)

Which Period 3 element has the highest melting point?

Which Group 2 hydroxide is least soluble?

Silver nitrate added to a halide solution gives a cream precipitate soluble in concentrated ammonia. The halide is

Which oxide forms an acidic solution in water?

What is the coordination number of Co in [Co(NH₃)₆]³⁺?

[Fe(H₂O)₆]³⁺ is more acidic than [Fe(H₂O)₆]²⁺ because Fe³⁺

Cracking long-chain alkanes produces

Which polymer is made by addition polymerisation?

Which alcohol is tertiary?

An IR absorption at 3230–3550 cm⁻¹ (broad) indicates

Enantiomers differ in their

Benzene undergoes substitution rather than addition because

Phenylamine is made from nitrobenzene using

Nylon-6,6 contains which linkage?

In DNA, the bases are attached to

How many peaks in the ¹³C NMR spectrum of propanone?

In column chromatography, the component eluted first is the one that