43 questions. Try each one, then open the answer to check yourself and read the explanation.
When a solid substance disappears completely as a gas on heating, the substance is said to have undergone
Answer: D (sublimation)
Sublimation is a change straight from solid to gas without melting, as with iodine or ammonium chloride.
A chemical reaction is always associated with
Answer: D (the formation of new substances)
The defining feature of a chemical change is that new substances are formed.
If a solution contains 4.9g of tetraoxosulphate(VI) acid, calculate the amount of copper (II) oxide that will react with it. [Cu = 64, O = 16, S = 32, H = 1]
Answer: B (4.0g)
H2SO4 + CuO → CuSO4 + H2O (1 : 1). 4.9 g ÷ 98 = 0.05 mol, so CuO needed = 0.05 × 80 = 4.0 g.
What volume of gas is evolved at s.t.p. if 2g of calcium trioxocarbonate (IV) is added to a solution of hydrochloric acid? [Ca = 40, C = 12, O = 16, Cl = 35.5, H = 1, Molar volume of a gas at s.t.p. = 22.4dm3]
Answer: C (448cm3)
CaCO3 (100 g/mol) gives one mole of CO2 per mole. 2 g = 0.02 mol, so CO2 = 0.02 × 22 400 = 448 cm3.
According to Charles' law, the volume of a gas becomes zero at
Answer: C (–273°C)
Extending Charles' law (V ∝ T) to zero volume gives absolute zero, 0 K = –273°C.
It is difficult to achieve an orderly arrangement of the molecules of a gas because they
Answer: B (have little force of attraction between them)
Gas molecules attract each other only very weakly, so nothing holds them in fixed, orderly positions; they move freely and randomly.
A given volume of methane diffuses in 20s. How long will it take the same volume of sulphur (IV) oxide to diffuse under the same conditions? [C = 12, H = 1, S = 32, O = 16]
Answer: C (40s)
By Graham's law, time ∝ √(molar mass). t = 20 × √(64/16) = 20 × 2 = 40 s.
An electron can be added to a halogen atom to form a halide ion with
Answer: D (8 valence electrons)
A halogen atom has 7 valence electrons; gaining one electron gives the halide ion a full octet of 8.
The shape of the s-orbital is
Answer: A (spherical)
An s-orbital is spherically symmetrical around the nucleus.
22688Ra → x86Rn + α – particle
What is the value of x in the nuclear reaction above?
Answer: B (222)
An alpha particle is 42He, so the mass number falls by 4: 226 – 4 = 222.
The property of chlorine which causes hydrogen chloride to be more ionic than the chlorine molecule is its
Answer: D (electronegativity)
Chlorine is much more electronegative than hydrogen, so it pulls the shared electrons towards itself, making H–Cl polar. In Cl2 both atoms pull equally.
Which of the following mixtures of gases is likely to burn in flame?
Answer: A (neon and hydrogen)
Hydrogen is flammable, so the mixture containing hydrogen can burn; the other gases are inert or do not burn.
In the experiment above, X is a mixture of nitrogen, carbon (IV) oxide and
Answer: C (inert gas)
Alkaline pyrogallol absorbs oxygen and anhydrous calcium chloride absorbs water vapour, so the gas leaving at X is mainly nitrogen with the inert (noble) gases.
Hardness of water is caused by the presence of the ions of
Answer: B (calcium and magnesium)
Dissolved Ca2+ and Mg2+ ions react with soap to form scum, which is what makes water hard.
Pollution of underground water by metal ions is very likely in a soil that has high
Answer: A (acidity)
Acid dissolves metal compounds in the soil, releasing metal ions that seep into groundwater. In alkaline soil metals stay as insoluble hydroxides.
A carcinogenic substance is
Answer: A (asbestos dust)
Breathing in asbestos fibres is known to cause lung cancer, so asbestos dust is carcinogenic.
The solubility in mol dm-3 of 20g of CuSO4 dissolved in 100g of water at 180°C is [Cu = 64, S = 32, O = 16]
Answer: C (1.25)
CuSO4 = 160 g/mol, so 20 g = 0.125 mol in 100 g (about 100 cm3) of water. Per 1000 cm3: 0.125 × 10 = 1.25 mol dm-3.
Which of these compounds is a normal salt?
Answer: D (Na2CO3)
A normal salt has all the replaceable hydrogen of the acid replaced by a metal. Na2CO3 has none left; the others are acid salts.
The oxidation state of chlorine in HClO4 is
Answer: D (+7)
+1 (H) + x + 4(–2) = 0, so x = +7.
ZnO(s) + CO(g) → Zn(s) + CO2(g) (heat)
In the reaction above, zinc has been
Answer: D (reduced)
Zinc goes from +2 in ZnO to 0 in Zn; it loses oxygen and gains electrons, so it is reduced.
In the electrolysis of brine, the anode is
Answer: D (carbon)
Chlorine attacks most metals, so an inert carbon (graphite) anode is used in the industrial electrolysis of brine.
The mass of silver deposited when a current of 10A is passed through a solution of silver salt for 4830s is [Ag = 108, F = 96500 C mol-1]
Answer: B (54.0g)
Q = 10 × 4830 = 48 300 C = 0.5 F. Ag+ + e- → Ag, so 0.5 mol Ag = 0.5 × 108 = 54 g.
Which of the following hydrogen halides has the highest entropy value?
Answer: D (HI)
Standard entropy rises with molar mass and number of electrons down the group (HF ≈ 174, HI ≈ 207 J K-1 mol-1), so HI has the highest.
N2O4(g) ⇌ 2NO2(g)
In the endothermic reaction above, more product formation will be favoured by
Answer: C (a decrease in pressure)
One gas molecule gives two, so lowering the pressure shifts the equilibrium towards the side with more molecules, NO2.
The allotrope of carbon used in the decolourization of sugar is
Answer: C (charcoal)
Animal (bone) charcoal has a huge surface area and adsorbs the coloured impurities from sugar solution.
Which of the following gases can be collected by the method of downward delivery?
Answer: A (chlorine)
Downward delivery suits gases denser than air. Chlorine is about 2.5 times as dense as air; ammonia and hydrogen are lighter, and oxygen is collected over water.
When steam is passed over red-hot carbon, the substances produced are
Answer: C (hydrogen and carbon (II) oxide)
C + H2O → CO + H2; this mixture of carbon(II) oxide and hydrogen is water gas.
Sulphur (IV) oxide bleaches by
Answer: A (reduction)
In water SO2 removes oxygen from (reduces) the dye to a colourless product; that is why its bleaching can wear off as air re-oxidises the dye.
Carbon is tetravalent because
Answer: C (the 2s and 2p atomic orbitals hybridize)
One 2s electron is promoted and the 2s and three 2p orbitals mix (sp3 hybridisation), giving four equivalent half-filled orbitals that form four bonds.
Aluminium hydroxide is used in the dyeing industry as a
Answer: C (mordant)
Aluminium hydroxide is a mordant: it sticks to the fibre and binds the dye to it so the colour does not wash out.
Alloys are best prepared by
Answer: D (cooling a molten mixture of the metals.)
Alloys are made by melting the metals together, mixing them and allowing the mixture to cool and solidify.
Transition metals possess variable oxidation states because they have
Answer: A (electrons in the d orbitals)
The 3d and 4s electrons are close in energy, so different numbers of d electrons can be used in bonding, giving several oxidation states.
Sodium metal is always kept under oil because it
Answer: C (reacts vigorously on exposure to air)
Sodium reacts rapidly with oxygen and moisture in air, so it is stored under paraffin oil to keep air away.
Oxyacetylene flame is used for iron-welding because it
Answer: C (evolves a lot of heat when burnt)
Ethyne burning in oxygen gives a very hot flame (about 3000°C), hot enough to melt iron.
The alkyl group can be represented by the general formula
Answer: A (CnH2n+1)
An alkyl group is an alkane (CnH2n+2) with one hydrogen removed: CnH2n+1, e.g. CH3–.
An isomer of C5H12 is
Answer: B (2 – methylbutane)
2-methylbutane has 5 carbons and 12 hydrogens. Butane and 2-methylpropane are C4H10; 2-ethylbutane is really a C6 compound (3-methylpentane).
A characteristic of the alkane family is
Answer: C (substitution reaction)
Alkanes are saturated, so they react by substitution, e.g. methane with chlorine in sunlight.
Which of these reagents can confirm the presence of a triple bond?
Answer: C (Copper (I) chloride)
Bromine water and KMnO4 are decolourised by both double and triple bonds. Ammoniacal copper(I) chloride gives a red precipitate only with alkynes having a terminal triple bond.
Vulcanization involves the removal of
Answer: C (the double bond)
In vulcanization, sulphur reacts at the C=C double bonds of rubber, forming cross-links, so the double bonds are used up.
CH3COOH(g) → CH4(g) + CO2(g)
The reaction above is
Answer: B (decarboxylation)
The –COOH group is removed as CO2, leaving methane: that is decarboxylation.
C2H5OH(aq) → Y (conc. H2SO4, 180°C)
In the reaction above, Y represents
Answer: C (C2H4)
Excess concentrated sulphuric acid at about 180°C removes water from ethanol (dehydration), giving ethene, C2H4.
Alkanol + Alkanoic acid ⇌ Ester + Water
The reverse reaction of the equation above is known as
Answer: A (hydrolysis)
The reverse of esterification is the breaking of an ester by water into the acid and alkanol, which is hydrolysis.
In the production of soap, concentrated sodium chloride solution is added to
Answer: B (decrease the solubility of the soap)
Adding brine lowers the solubility of soap so it separates out as a solid on top (salting out).