17 questions. Try each one, then open the answer to check yourself and read the explanation.
Calculate the number of moles of (H+) present in 1dm3 of 0.5m solution of H2SO4?
Answer: A (1.0 mole)
1 dm3 of 0.5 M H2SO4 holds 0.5 mol of acid. Each H2SO4 gives 2H+, so there are 2 × 0.5 = 1.0 mol of H+.
Determine the PH of a 2.50×10−5M solution of potassium hydroxide.
Answer: B (9.4)
KOH ionises fully, so [OH−] = 2.5 × 10−5 and pOH = −log(2.5 × 10−5) ≈ 4.6. pH = 14 − 4.6 = 9.4.
2CO(g) + O2(g) → 2CO2(g)
In the above reaction, the standard heats of formation of CO(g) and CO2(g) are −297KJmol−1 and −396KJmol−1 respectively. The heat change of the reaction is
Answer: C (−198KJmol−1)
ΔH = Σ products − Σ reactants = 2(−396) − 2(−297) = −792 + 594 = −198 kJ mol−1 (O2 is an element, so its value is 0).
The rate law obtained for a given reaction is expressed as r = K [X]n [Y]m. The overall order of the reaction becomes.
Answer: D (n+m)
The overall order is the sum of the powers on the concentrations in the rate law: n + m.
A filter paper soaked in lead ethanoate solution will turn black in the presence of
Answer: C (hydrogen sulphide gas)
H2S reacts with lead ethanoate to form black lead(II) sulphide, PbS; this is the test for hydrogen sulphide.
Which of the following is an aromatic compound?
Answer: D (C6H5OH)
C6H5OH is phenol, which contains a benzene ring; the others are open-chain (aliphatic) compounds.
Which of these hydrocarbons burns in air with a sooty flame?
Answer: B (C6H6)
Benzene, C6H6, has a high carbon-to-hydrogen ratio, so it burns incompletely and gives a smoky, sooty flame; the alkanes burn cleanly.
A compound composed of Al, Si, O and H is?
Answer: B (clay)
Clay (kaolin) is hydrated aluminium silicate, Al2Si2O5(OH)4, made of Al, Si, O and H.
The vapour density of XO2(g) given as 32, calculate the atomic mass of X
Answer: C (32)
Relative molecular mass = 2 × vapour density = 64. X + 2(16) = 64, so X = 32.
CH3COOH is
Answer: B (monobasic)
Only the hydrogen of the –COOH group ionises (CH3COOH ⇌ CH3COO− + H+), so ethanoic acid is monobasic.
Which of these salts will give a precipitate when treated with NaOH solution?
Answer: B (AlCl3)
Al3+ + 3OH− → Al(OH)3, a white gelatinous precipitate. NH4Cl gives ammonia gas, and the sodium salts give no change.
Which of the following elements can catenate?
Answer: A (carbon)
Catenation is the ability of atoms of an element to join to each other in long chains and rings; carbon shows this strongly.
What is the ratio of carbon : hydrogen :oxygen in carbohydrate?
Answer: A (1:2:1)
Carbohydrates have the general formula Cx(H2O)y; for glucose, C6H12O6, C : H : O = 6 : 12 : 6 = 1 : 2 : 1.
Vulcanization deals with the removal of
Answer: B (the double bond)
In vulcanization sulphur reacts at the C=C double bonds of natural rubber, forming cross-links and using up double bonds; this makes the rubber harder and less sticky.
Ammonia gas reacts with which of the following to form a dense white fume?
Answer: C (HCl(g))
NH3 + HCl → NH4Cl; the tiny solid particles of ammonium chloride form dense white fumes.
The alloy that contain iron from the following is
Answer: D (steel and pemalloy)
Steel is iron with carbon, and permalloy is iron with nickel; brass, bronze, solder and duralumin contain no iron (duralumin is mostly aluminium).
Which of these is an unsaturated hydrocarbon?
Answer: D (propene)
Propene, CH3CH=CH2, has a C=C double bond and undergoes addition, so it is unsaturated; butanol is not a hydrocarbon and pentane is saturated.