50 questions. Try each one, then open the answer to check yourself and read the explanation.
Figure 1 above shows part of the Periodic Table. Which of the elements belongs to the p-block?
Answer: D (P, Q and R)
The p-block is the block of six columns on the right of the Periodic Table (groups 3 to 0). Only P, Q and R are in that block; V, W and X are in the s-block and S, T and U are in the middle (d-block).
Which of the following conducts electricity?
Answer: B (Graphite)
In graphite each carbon uses only three of its four outer electrons for bonding; the fourth is free to move between the layers and carry current.
An organic compound contains 72% carbon, 12% hydrogen and 16% oxygen by mass. The empirical formula of the compound is (H = 1, C = 12, O = 16).
Answer: D (C6H12O)
Moles: C 72/12 = 6, H 12/1 = 12, O 16/16 = 1. The simplest ratio is 6 : 12 : 1, so the empirical formula is C6H12O.
0.499 g of CuSO4.xH2O when heated to constant weight gave a residue of 0.346 g. The value of x is (Cu = 63.5, S = 32.0, O = 16, H = 1).
Answer: D (4.0)
Water lost = 0.499 − 0.346 = 0.153 g = 0.0085 mol. CuSO4 left = 0.346/159.5 = 0.00217 mol. Ratio 0.0085 : 0.00217 ≈ 4, so x = 4.
In an experiment, which of the following observations would suggest that a solid sample is a mixture? The
Answer: C (solid begins to melt at 573 K but is not completely melted until 648 K)
A pure solid melts sharply at one temperature. A sample that melts over a wide range of temperatures (573 K to 648 K) must contain more than one substance.
Hydrogen diffuses through a porous plug
Answer: E (four times as fast as oxygen.)
By Graham's law, rate is inversely proportional to the square root of the molar mass: rate(H2)/rate(O2) = √(32/2) = √16 = 4.
Given that the molecular mass of iron is 56 and that of oxygen is 16, how many moles of iron (III) oxide will be contained in 1 kg of the compound?
Answer: C (6.25 moles)
Molar mass of Fe2O3 = 2 × 56 + 3 × 16 = 160 g. Moles in 1000 g = 1000/160 = 6.25.
3.0 g of a mixture of potassium carbonate and potassium chloride were dissolved in a 250 cm3 standard flask. 25cm3 of this solution required 40.00 cm3 of 0.1 M HCl for neutralization. What is the percentage by weight of K2CO3 in the mixture (K = 39, O = 16, C = 12).
Answer: E (92)
HCl used = 0.040 × 0.1 = 0.004 mol, which reacts with 0.002 mol of K2CO3 (K2CO3 + 2HCl). The whole 250 cm3 holds 0.02 mol × 138 g = 2.76 g, and 2.76/3.0 × 100 = 92%.
Figure 2 represents the solubility curves of two salts, X and Y, in water. At room temperature (300 K)
Answer: A (Y is twice as soluble as X)
At 300 K the graph gives about 20 g of X but about 38 g of Y per 100 g of water, so Y is roughly twice as soluble as X.
Figure 2 represents the solubility curves of two salts, X and Y, in water. If 80 g each of X and Y are taken up in 100 g of water at 353 K we shall have
Answer: B (only 16 g of Y undissolved)
At 353 K up to about 82 g of X dissolves in 100 g of water, so all 80 g of X dissolves. Only about 64 g of Y can dissolve, leaving 80 − 64 = 16 g of Y undissolved.
Figure 2 represents the solubility curves of two salts, X and Y, in water. If the molar mass of X is 36 g, the number of moles of X dissolved at 343 K is
Answer: D (2.0 moles)
From the graph, about 70 g of X dissolves in 100 g of water at 343 K. Moles = 70/36 ≈ 1.9, which is closest to 2.0 moles.
Some properties of chemical substances are mentioned below (i) sour taste (ii) slippery to touch (iii) yields alkaline gas with ammonium salts (iv) has pH less than 7 (v) turns phenolphthalein pink. Which of the above are NOT typical properties of alkalis?
Answer: C ((i) and (iv))
A sour taste and a pH below 7 are properties of acids. Alkalis feel slippery, release ammonia from ammonium salts and turn phenolphthalein pink.
A certain volume of a gas at 298 K is heated such that its volume and pressure are now four times the original values. What is the new temperature?
Answer: E (4768.0 K)
PV/T is constant, so if P and V are each multiplied by 4, T is multiplied by 16: 298 × 16 = 4768 K.
Hydrogen is not liberated when trioxonitrate (V) acid reacts with zinc because
Answer: B (hydrogen produced is oxidized to water)
Trioxonitrate (V) acid is a powerful oxidising agent. Any hydrogen formed is at once oxidised to water, and the acid is reduced to oxides of nitrogen instead.
The boiling points of water, ethanol, toluene and butan-2-ol are 373. OK, 351.3K, 383.6 K and 372.5 K respectively. Which liquid has the highest vapour pressure at 323.0 K?
Answer: C (Ethanol)
The liquid with the lowest boiling point evaporates most easily, so at any temperature it has the highest vapour pressure. Ethanol boils lowest (351.3 K).
In what respect will two dry samples of nitrogen gas differ from each other if sample 1 is prepared by completely removing CO2 and O2 from air, and sample 2 is prepared by passing purified nitrogen (i) oxide over heated copper? Sample 1 is
Answer: B (slightly denser than sample 2)
Nitrogen from air still contains about 1% of the noble gases, mainly argon, which is heavier than nitrogen. So it is slightly denser than pure nitrogen made chemically.
Copper sulphate solution is electrolysed using platinum electrodes. A current of 0.193 amperes is passed for 2 hrs. How many grams of copper are deposited? (Cu = 63.5, F = 96500 coulombs).
Answer: A (0.457 g)
Charge = 0.193 × 2 × 3600 = 1389.6 C. Cu2+ needs 2 × 96500 C per mole (63.5 g), so mass = 63.5 × 1389.6 / 193000 = 0.457 g.
X + Y ⇌ Z is an equilibrium reaction. The addition of a catalyst.
Answer: B (increases the rate of change in concentrations of X, Y and Z)
A catalyst speeds up both the forward and backward reactions equally, so all the concentrations change faster and equilibrium is reached sooner. It does not change the amounts present at equilibrium.
What is the formula of sodium gallate if gallium (Ga) shows an oxidation number of + 3?
Answer: D (NaGa(OH)4)
In NaGa(OH)4: (+1) + Ga + 4(−1) = 0, so Ga = +3. Gallium is in the same group as aluminium, which forms NaAl(OH)4.
If the ONLY pollutants found in the atmosphere over a city are oxides of nitrogen, suspended lead compounds. carbon monoxide and high levels of methane, the probable source(s) of the pollution must be
Answer: A (automobile exhaust and biological decomposition)
Car exhaust gives oxides of nitrogen, lead compounds (from leaded petrol) and carbon monoxide; methane comes from rotting (biological decomposition). Coal burning would also give SO2, which is absent.
A correct electrochemical series can be obtained from K, Na, Ca, Al, Mg, Zn, Fe, Pb, H, Cu, Hg, Ag, Au by interchanging
Answer: A (Al and Mg)
The correct order is K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au. Magnesium is more reactive than aluminium, so they must be swapped.
A certain industrial process is represented by the chemical equation 2A(g) + B(g) ⇌ C(g) + 3D(g) ΔH = X kJ mol−1. Which of the following conditions will favour the yield of the products?
Answer: A (increase in temperature, decrease in pressure)
The products side has more gas molecules (4 against 3), so a lower pressure shifts the equilibrium to the right. Taking ΔH = +X (endothermic), a higher temperature also shifts it to the right.
2MnO4− + 10Cl− + 16H+ → 2Mn2+ + 5Cl2 + 8H2O. Which of the substances serves as an oxidizing agent?
Answer: D (MnO4)
Manganese goes from +7 in MnO4− to +2 in Mn2+, so the manganate (VII) ion is reduced. It takes electrons from Cl−, so it is the oxidising agent.
In the reaction H2O(g) ⇌ H2(g) + ½O2(g) ΔH = −243600 kJ, which of the following has no effect on the equilibrium position?
Answer: A (Adding argon to the system)
Argon does not take part in the reaction and, added at constant volume, does not change the partial pressures of the reacting gases. Changing temperature, pressure or the amount of hydrogen all shift the equilibrium.
Which of the following metals will displace iron from a solution of iron (II) tetraoxosulphate (IV)?
Answer: D (Zinc)
A metal displaces another from its salt only if it is higher in the electrochemical series. Zinc is above iron; copper, mercury, silver and gold are below it.
Complete hydrogenation of ethyne yields
Answer: C (ethane)
Ethyne adds two molecules of hydrogen: C2H2 + 2H2 → C2H6. Complete hydrogenation gives ethane; ethene is only the halfway product.
Which of the following is used in the manufacture of bleaching powder?
Answer: B (Chlorine)
Bleaching powder is made by passing chlorine over slaked lime, Ca(OH)2.
A man suspected of being drunk is made to pass his breath into acidified potassium dichromate solution. If his breath carries a significant level of ethanol, the final colour of the solution is
Answer: E (green)
Ethanol reduces the orange dichromate (VI) ion to green chromium (III) ions, so the solution turns from orange to green.
When pollen grains are suspended in water and viewed through a microscope, they appear to be in a state of constant but erratic motion. This is due to
Answer: E (the bombardment of the pollen grains by molecules of water)
This is Brownian motion: the moving water molecules hit the pollen grains unevenly from all sides, pushing them about at random.
The energy change (ΔH) for the reaction CO(g) + ½O2(g) → CO2(g) is (ΔHf(CO) = −110.4 kJ mol−1) (ΔHf(CO2) = −393 kJ mol−1)
Answer: C (−282.9 kJ)
ΔH = (heats of formation of products) − (heats of formation of reactants) = −393 − (−110.4 + 0) ≈ −283 kJ, so the answer is −282.9 kJ.
The products formed on hydrolysis of CH3COOCH2CH2CH3 (shown) in acid (HCl) is
Answer: C (CH3CO–O–H + HOCH2CH2CH3)
Acid hydrolysis of an ester gives back the acid and the alcohol it was made from. Propyl ethanoate gives ethanoic acid and propan-1-ol (HOCH2CH2CH3).
The neutralization reaction between NaOH solution and nitrogen (IV) oxide (NO2) produces water and
Answer: A (NaNO2 and NaNO3)
NO2 reacts with alkali as a mixture of two acids: 2NO2 + 2NaOH → NaNO2 + NaNO3 + H2O. Both sodium dioxonitrate (III) and sodium trioxonitrate (V) are formed.
The oxidation of CH3—CH2—CH(CH3)—OH (shown) gives
Answer: A (2-butanone)
The compound is butan-2-ol, a secondary alcohol. Oxidising a secondary alcohol gives a ketone, butan-2-one.
Tetraoxosulphate (VI) ions are finally tested using
Answer: B (acidified barium chloride)
Adding barium chloride acidified with dilute HCl to a sulphate solution gives a white precipitate of barium sulphate that does not dissolve in the acid.
The I.U.P.A.C name for the compound CH3—CH(CH3)—CH = CH—CH3 is
Answer: B (4-methyl-2-pentene)
Number the five-carbon chain from the end nearer the double bond: the double bond starts at carbon 2 and the methyl group is on carbon 4, giving 4-methylpent-2-ene (4-methyl-2-pentene).
Mixing of aqueous solutions of barium hydroxide and sodium tetraoxocarbonate (IV) yields a white precipitate of
Answer: E (barium tetraoxocarbonate (IV).)
Ba(OH)2 + Na2CO3 → BaCO3 + 2NaOH. Barium carbonate is insoluble and comes out as a white precipitate; NaOH stays in solution.
An organic compound decolorized acidified KMnO4 solution but failed to react with ammoniacal silver nitrate solution. The organic compound is likely to be
Answer: C (an alkene)
Decolourising KMnO4 shows a C=C or C≡C bond. Alkynes like ethyne give a precipitate with ammoniacal silver nitrate, alkenes do not, so it is an alkene.
Solid sodium hydroxide on exposure to air absorbs a gas and ultimately gives another alkaline substance with the molecular formula
Answer: C (Na2CO3)
NaOH absorbs carbon (IV) oxide from the air: 2NaOH + CO2 → Na2CO3 + H2O. Sodium carbonate is also alkaline.
Which of the following is the functional group of carboxylic acids?
Answer: D (—C(=O)OH)
Carboxylic acids contain the carboxyl group, –COOH: a carbon joined to both a C=O oxygen and an –OH.
Which of the following substances is the most abundant in the universe?
Answer: E (Hydrogen)
Hydrogen is the most abundant element in the universe; stars such as the sun are made mostly of hydrogen.
A colourless organic compound X was burnt in excess air to give two colourless and odourless gases, Y and Z, as products. X does not decolorize bromine vapour, Y turns lime milky while Z gives a blue colour with copper (II) tetraoxosulphate (VI). Compound X is
Answer: B (an alkane)
Burning gives only CO2 (turns limewater milky) and water (turns anhydrous CuSO4 blue), so X is a hydrocarbon. It does not decolourise bromine, so it is saturated: an alkane.
A colourless organic compound X was burnt in excess air to give two colourless and odourless gases, Y and Z, as products. X does not decolorize bromine vapour, Y turns lime milky while Z gives a blue colour with copper (II) tetraoxosulphate (VI). Y and Z are respectively
Answer: D (CO2 and H2O)
Y turns limewater milky, so it is CO2. Z turns white anhydrous copper (II) sulphate blue, so it is water vapour.
Which of the following compounds is NOT the correct product formed when the parent metal is heated in air?
Answer: B (Sodium oxide (Na2O))
Heated iron forms tri-iron tetroxide, and calcium, copper and aluminium form the oxides listed. Sodium burns in air to give mainly sodium peroxide, Na2O2, not Na2O.
The atomic number of an element whose cation, X2+, has the ground state electronic configuration 1s22s22p63s23p6 is
Answer: C (20)
The ion has 18 electrons. The atom lost 2 electrons to form X2+, so it had 20 electrons and an atomic number of 20 (calcium).
When marble is heated to about 1473 K, another white solid is obtained which reacts vigorously with water to give an alkaline solution. The solution contains
Answer: E (Ca(OH)2.)
Marble (CaCO3) decomposes to quicklime, CaO. Quicklime reacts vigorously with water to give calcium hydroxide, Ca(OH)2.
Addition of dilute hydrochloric acid to an aqueous solution of a crystalline salt yielded a yellow precipitate and a gas which turned dichromate paper green. The crystalline salt was probably
Answer: C (Na2S2O3.5H2O)
Acid decomposes sodium thiosulphate into a yellow precipitate of sulphur and sulphur (IV) oxide gas. SO2 turns orange dichromate paper green.
The process involved in the conversion of an oil into margarine is known as
Answer: A (hydrogenation)
Hydrogen is added to the C=C bonds of the liquid oil (with a nickel catalyst), making it more saturated and solid like margarine.
An aqueous solution of an inorganic salt gave white precipitate (i) soluble in excess aqueous NaOH (ii) insoluble in excess aqueous NH3 (iii) with dilute HCl. The cation present in the inorganic salt is
Answer: E (Pb2+.)
Lead (II) ions give a white Pb(OH)2 precipitate that dissolves in excess NaOH but not in excess ammonia, and dilute HCl gives white lead (II) chloride. Al3+ gives no precipitate with HCl.
Which of the following roles does sodium chloride play in soap preparation? It
Answer: D (separates the soap from the glycerol)
Soap is less soluble in strong salt solution, so adding NaCl makes the soap come out of the mixture while the glycerol stays dissolved. This is called salting out.
The function of sulphur during the vulcanization of rubber is to
Answer: C (form chains which bind rubber molecules together)
In vulcanisation, sulphur atoms form cross-links between neighbouring rubber chains. This makes the rubber harder, stronger and less sticky.