47 questions. Try each one, then open the answer to check yourself and read the explanation.
The addition of water to calcium oxide leads to
Answer: B (a chemical change)
Water reacts with calcium oxide to form a new substance, calcium hydroxide (slaked lime), with a lot of heat given out. A new substance means a chemical change.
A mixture of iron and sulphur can be separated by dissolving the mixture in
Answer: D (benzene)
Sulphur dissolves in organic solvents such as benzene (or carbon disulphide) but iron does not, so the sulphur can be dissolved away and the iron filtered off. Dilute HCl would react with the iron instead of separating it.
8.0 g of an element X reacted with an excess of copper (II) tetraoxosulphate (VI) solution to deposit 21.3g of copper. The correct equation for the reaction is [Cu = 64].
Answer: A (X(s) + CuSO4(aq) → Cu(s) + XSO4(aq))
21.3 g of Cu is 21.3/64 ≈ 0.333 mol. With a 1 : 1 ratio, 8.0 g of X is also 0.333 mol, so X has relative atomic mass 24, which is magnesium, a real divalent metal that displaces copper. The other ratios give masses that match no suitable metal.
C3H8(g) + 5O2(g) → 4H2O(g) + 3CO2(g). From the equation above, the volume of oxygen at s.t.p. required to burn 50cm3 of propane is
Answer: A (250cm3)
By Gay-Lussac's law, gas volumes react in the ratio of the coefficients: 1 volume of propane needs 5 volumes of oxygen, so 50 × 5 = 250 cm3.
30cm3 of hydrogen was collected over water at 27°C and 780 mm Hg. If the vapour pressure of water at the temperature of the experiment was 10 mm Hg, calculate the volume of the gas at 760 mm Hg and 7°C.
Answer: C (28.4 cm3)
Pressure of dry hydrogen = 780 − 10 = 770 mmHg at 300 K. V2 = 770 × 30 × 280/(300 × 760) ≈ 28.4 cm3.
A given amount of gas occupies 10.0 dm3 at 4 atm, and 273°C. The number of moles of the gas present is [Molar volume of a gas at s.t.p. = 22.4 dm3]
Answer: A (0.89 mol)
Convert to s.t.p.: V = 10.0 × 4 × 273/546 = 20 dm3. Moles = 20/22.4 ≈ 0.89 mol.
If sulphur (IV) oxide and methane are released simultaneously at the opposite ends of a narrow tube, the rates of diffusion RSO2 and RCH4 will be in the ratio [S = 32, O = 16, C = 12, H = 1]
Answer: C (1:2)
Rate is inversely proportional to √(molar mass). R(SO2)/R(CH4) = √(16/64) = 1/2, so the ratio is 1 : 2.
A solid begins to melt when
Answer: D (energy of vibration of particles of the solid equals the intermolecular forces.)
As a solid is heated, its particles vibrate more and more. Melting begins when this vibrational energy is equal to the forces holding the particles in their fixed positions, so they can start to move past one another.
The diagram above represents an atom that can combine with chlorine to form
Answer: B (an electrovalent bond)
The atom shown has only two electrons in its outermost shell, so it is a metal that easily loses them. A metal losing electrons to chlorine forms ions, which is an electrovalent (ionic) bond.
Which of the following electron configurations indicates an atom with the highest ionization energy?
Answer: A (2, 8, 7)
Ionization energy is highest for a small atom with a nearly full outer shell. 2, 8, 7 (chlorine) has fewer shells than 2, 8, 8, 7, so its outer electrons are held most tightly; the 1- and 2-electron metals lose electrons easily.
The line observed in the simple hydrogen spectrum are due to emission of
Answer: C (energy by electron transition)
Each line comes from light given out when an electron falls from a higher energy level to a lower one, releasing a fixed amount of energy.
If an element X of atomic number Z and mass number Y is irradiated by an intense concentration of neutrons, the relevant nuclear equation is
Answer: B (YZX + 10n → Y+1ZX)
Capturing a neutron adds 1 to the mass number but leaves the number of protons (atomic number) unchanged, giving a heavier isotope of the same element.
The property used in obtaining oxygen and nitrogen industrially from air is the
Answer: A (boiling point)
Air is liquefied and then fractionally distilled; nitrogen and oxygen separate because they have different boiling points.
Potassium tetraoxomanganate (VII) is often added to impure water to
Answer: C (destroy bacteria and algae)
KMnO4 is a strong oxidizing agent and acts as a disinfectant, killing bacteria and algae in the water.
The soil around a battery manufacturing factory is likely to contain a high concentration of
Answer: B (Pb2+ salts)
Car batteries (lead-acid accumulators) are made from lead and lead compounds, so waste from such a factory pollutes the soil with lead salts.
90.0g of MgCl2 was placed in 50.0cm3 of water to give a saturated solution at 298K. If the solubility of the salt is 8.0 mol dm−3 at the same temperature, what is the mass of the salt left undissolved at the given temperature? [Mg = 24, Cl = 35.5]
Answer: A (52.0g)
Molar mass of MgCl2 = 95. 50 cm3 dissolves 8.0 × 0.050 = 0.40 mol = 38 g. Undissolved = 90 − 38 = 52 g.
Soap lather is an example of a colloid in which
Answer: C (gas is dispersed in liquid)
Lather (foam) is made of tiny air bubbles trapped in soapy water, so a gas is dispersed in a liquid.
The pH of a solution obtained by mixing 100cm3 of a 0.1M HCl solution with 100cm3 of a 0.2M solution of NaOH is
Answer: D (12.7)
HCl = 0.01 mol and NaOH = 0.02 mol, so 0.01 mol of OH− is left in 200 cm3: [OH−] = 0.05 M. pOH = −log 0.05 = 1.3, so pH = 14 − 1.3 = 12.7.
In the conductance of aqueous potassium tetraoxosulphate (VI) solution, the current carriers are the
Answer: C (hydrated ions)
In a solution, electricity is carried by moving ions, not electrons. In water each K+ and SO42− ion is surrounded by water molecules, so the carriers are hydrated ions.
What volume of 0.1 mol dm−3 solution of tetraoxosulphate (VI) acid would be needed to dissolve 2.86g of sodium trioxocarbonate (IV) decahydrate crystals? [H = 1, C = 12, O = 16, S = 32, Na = 23].
Answer: D (100cm3)
Na2CO3.10H2O has molar mass 286, so 2.86 g = 0.01 mol. It reacts 1 : 1 with H2SO4, so 0.01 mol of acid is needed: 0.01/0.1 = 0.1 dm3 = 100 cm3.
1.2F of electricity are passed through electrolytic cells containing Na+, Cu2+ and Al3+ in series. How many moles of each metal would be formed at the cathode of each cell?
Answer: B (1.2 moles of Na, 0.6 mole of Cu and 0.4 mole of Al)
Moles of metal = faradays ÷ charge on the ion: Na 1.2/1 = 1.2, Cu 1.2/2 = 0.6, Al 1.2/3 = 0.4.
What mass of gold is deposited during the electrolysis of gold (III) tetraoxosulphate (VI) when a current of 15A is passed for 193 seconds? [Au = 97, F = 96500C mol−1].
Answer: A (1.97g)
Q = 15 × 193 = 2895 C = 0.03 F. Au3+ needs 3 F per mole, so 0.01 mol of gold is deposited. With the true Au = 197 this is 1.97 g.
Fe(s) + Cu2+(aq) → Fe2+(aq) + Cu(s). From the reaction above, it can be inferred that
Answer: D (Cu2+ is the oxidising agent.)
Cu2+ gains two electrons from iron and becomes Cu. A species that takes electrons is reduced and is the oxidising agent.
2FeCl2(s) + Cl2(g) → 2FeCl3(s). The reducing agent in the reaction above is
Answer: A (FeCl2)
Iron goes from +2 in FeCl2 to +3 in FeCl3, so FeCl2 loses electrons (is oxidized) and is the reducing agent.
The reaction that is accompanied by a decrease in entropy when carried out at constant temperature is
Answer: B (N2(g) + 3H2(g) ⇌ 2NH3(g))
Entropy (disorder) falls when the number of gas molecules falls. In B, 4 moles of gas become 2 moles; the other reactions produce more gas.
32g of anhydrous copper (II) tetraoxosulphate (VI) dissolved in 1dm3 of water generated 13.0kJ of heat. The heat of solution is [Cu = 64, S = 32, O = 16]
Answer: B (65.0 k Jmol−1)
Molar mass of CuSO4 = 160, so 32 g = 0.2 mol. Heat per mole = 13.0/0.2 = 65.0 kJ mol−1 (given out, so ΔH = −65 kJ mol−1).
Mg2+(aq) + 2e− → Mg(s) E° = −2.370 volts
Zn2+(aq) + 2e− → Zn(s) E° = −0.763 volts
Cd2+(aq) + 2e− → Cd(s) E° = −0.403 volts
Cu2+(aq) + 2e− → Cu(s) E° = +0.340 volts
In the electrochemical series above, the strongest reducing agent is
Answer: D (Mg(s))
The metal with the most negative electrode potential gives up electrons most easily, so it is the strongest reducing agent. Magnesium (−2.37 V) is strongest; copper (+0.34 V) is the weakest.
In the diagram above, the activation energy for the backward reaction is
Answer: C (+25kJ)
The backward reaction starts from the products (2PQ, about 15 kJ on the graph) and must climb to the top of the peak (40 kJ). So its activation energy is about 40 − 15 = 25 kJ.
2X(g) + Y(g) → Z(g). In the equation above, the rate of formation of Z is found to be independent of the concentration of Y and to quadruple when the concentration of X is doubled. The correct equation for the reaction is
Answer: D (R = k[X]2[Y]0)
Doubling [X] makes the rate 4 = 22 times faster, so the order in X is 2. The rate does not depend on Y, so its power is 0.
2Cl2(g) + 2H2O(g) ⇌ 4HCl(g) + O2(g) ΔH° = +115kJ mol−1. In the above equilibrium reaction, a decrease in temperature will
Answer: A (favour the reverse reaction)
The forward reaction is endothermic. Cooling favours the exothermic direction, which here is the reverse reaction.
3CuO(s) + 2NH3(g) → 3Cu(s) + 3H2O(l) + N2(g) (i)
2NH3(g) + 3Cl2(g) → 6HCl(g) + N2(g) (ii)
4NH3(g) + 3O2(g) → 6H2O(l) + 2N2(g) (iii)
The reactions represented by the equations above demonstrate the
Answer: C (reducing properties of ammonia)
In each reaction the nitrogen in NH3 goes from −3 to 0 in N2; ammonia is oxidized, so it acts as a reducing agent.
A gas that turns a filter paper previously soaked in lead ethanoate solution black is
Answer: B (hydrogen sulphide)
Hydrogen sulphide reacts with lead ethanoate to form black lead(II) sulphide; this is the standard test for H2S.
In the experiment above, X could be a solution of
Answer: B (sodium trioxonitrate (III) and ammonium chloride)
Nitrogen is prepared in the laboratory by warming a mixture of sodium nitrite (sodium dioxonitrate(III)) and ammonium chloride; the gas is collected over water.
The oxide that remains unchanged when heated in hydrogen is
Answer: D (ZnO)
Hydrogen can reduce the oxides of less reactive metals such as copper, lead and iron to the metal. Zinc is too high in the activity series, so heating ZnO in hydrogen leaves it unchanged.
Which of the following is observed when a solution of iron (III) chloride is mixed with a solution of sodium hydroxide?
Answer: D (A brown precipitate is formed)
Fe3+ ions react with OH− to give reddish-brown iron(III) hydroxide precipitate.
A common characteristic shared by iron and aluminium is that both
Answer: A (are extracted by reduction methods)
Both metals are obtained from their ores by reduction: iron by carbon(II) oxide in the blast furnace and aluminium by electrolytic reduction. Aluminium oxide is amphoteric, aluminium shows only +3, and both hydroxides are insoluble.
Alloys are often used in preference to pure metals because
Answer: C (metallic properties are improved in alloys)
Alloying improves properties such as hardness, strength and resistance to corrosion, which is why alloys are chosen over pure metals.
CH3CH2CH(OH)CH(CH3)2
The IUPAC nomenclature for the above compound is
Answer: B (2-methylpentan-3-ol)
The longest chain has five carbons with OH on C3 from either end. Numbering to give the methyl branch the lower number puts it on C2: 2-methylpentan-3-ol.
Dehydration of CH3-CH2-CH2-CH2-OH gives
Answer: A (CH2 = CH-CH2-CH3)
Removing a water molecule from butan-1-ol (the OH and an H from the next carbon) forms a C=C double bond, giving but-1-ene, CH2=CHCH2CH3. Dehydration gives an alkene, not an alkyne.
nCH2=CH2 → (-CH2-CH2-)n [O2 (initiator), 1,500 atm, 473K]. The above equation represents the manufacture of
Answer: B (polythene)
Ethene molecules join together by addition polymerization at high pressure to form polythene (poly(ethene)).
One mole of a hydrocarbon contains 6g of hydrogen. If the molecular weight is 54, the hydrocarbon is an
Answer: D (alkyne)
6 g of H means 6 H atoms. 54 − 6 = 48 g of carbon = 4 C atoms, so the formula is C4H6, which fits CnH2n−2, an alkyne (butyne).
The products obtained when a pure hydrocarbon is burnt in excess oxygen are
Answer: D (carbon (IV) oxide and water.)
Complete combustion of a hydrocarbon turns all the carbon into carbon(IV) oxide and all the hydrogen into water.
How many structural isomers can be drawn for the non-cyclic alkanol with molecular formula C4H10O?
Answer: D (4)
There are four butanols: butan-1-ol, butan-2-ol, 2-methylpropan-1-ol and 2-methylpropan-2-ol.
On cracking medicinal paraffin, a gas is evolved which gives a pop sound with a lighted splinter and an oily liquid which decolourizes bromine solution is also obtained. The products of the cracking are
Answer: C (hydrogen gas and alkene)
A gas that burns with a pop is hydrogen. A liquid that decolourizes bromine is unsaturated, an alkene.
An example of aromatic compound is
Answer: C (C6H5OH)
Aromatic compounds contain a benzene ring (C6H5–). C6H5OH is phenol; the others are aliphatic hexane derivatives.
Terylene is synthesized from ethane-1, 2-diol and benzene-1, 4-dicarboxylic acid by
Answer: B (condensation reaction)
The diol and the diacid join through ester links and lose a water molecule at each link, so terylene is a condensation polymer.
Which of the following is true concerning the properties of benzene and hexane?
Answer: A (Both undergo substitution reaction.)
Hexane is saturated and benzene is very stable, so both mainly undergo substitution reactions (e.g. with chlorine). Both are liquids and neither readily decolourizes bromine water.