20 questions. Try each one, then open the answer to check yourself and read the explanation.
A chemical reaction involving the absorption of heat is said to be
Answer: B (endothermic)
A reaction that takes in heat from the surroundings is endothermic (ΔH positive).
What element is common in the two alloys: brass and bronze?
Answer: D (Copper)
Brass is copper and zinc; bronze is copper and tin. Copper is in both.
Bubbling of CO2 into Ca(OH)2(aq) a white precipitate is formed. In the presence of carbon dioxide (in excess) the white precipitate disappears. The reason for this is
Answer: D (calcium carbonate is formed which on reaction with further carbondioxide forms soluble calcium hydrogen carbonate)
CO2 first gives insoluble CaCO3 (milky); excess CO2 and water turn it into soluble Ca(HCO3)2, so the precipitate clears.
The organic compound above is
Answer: A (2, 3-dimethylpent-2-ene)
The longest chain has 5 carbons. Numbering from the end nearer the double bond puts the C=C at carbon 2 and the methyl groups on carbons 2 and 3: 2,3-dimethylpent-2-ene.
The solubility graph of a solid Y (molecular mass=160) as shown below. 1000cm3 of a saturated solution of Y at 80°C is cooled to 40°C. The weight of Y crystalized out would be
Answer: B (16g)
From the graph, solubility is 0.4 mol/dm3 at 80 °C and 0.3 mol/dm3 at 40 °C. 0.1 mol crystallises: 0.1 × 160 = 16 g.
Which of the following is a neutral oxide
Answer: C (CO)
CO reacts with neither acids nor alkalis, so it is neutral; NO2 and CO2 are acidic and Al2O3 is amphoteric.
CuSO4(aq) is electrolyzed using platinum electrodes with a current of 0.193 amperes for 2 hours. How many grams of copper are deposited at the cathode? [Cu= 63.5 F=96500 coulombs]
Answer: B (0.457g)
Q = It = 0.193 × 7200 = 1389.6 C. Cu2+ needs 2 × 96500 C per mole, so mass = 1389.6/193000 × 63.5 ≈ 0.457 g.
Write out the values of a, b and c respectively in the equation. aCu + bHNO3 → aCu(NO3)2 + 4H2O + cNO
Answer: A (3:8:2)
The balanced equation is 3Cu + 8HNO3 → 3Cu(NO3)2 + 4H2O + 2NO, so a = 3, b = 8, c = 2.
A compound used as an 'anti-knock' in automobile engines is
Answer: C (lead tetra-ethyl)
Tetraethyl lead was added to petrol to stop knocking (n-heptane actually causes knocking).
Which of the compounds has the lowest vapour density? [O= 16, Cl= 35.5, H= 1, C= 12]
Answer: C (Ethanal)
Vapour density = Mr/2. Propanol 60, ethanoic acid 60, ethanal 44, dichloromethane 85; ethanal gives the lowest (22).
Calculate the volume of 0.1mH2SO4 that will be required to neutralize 45.0cm3 of a 0.2 MNaOH?
Answer: C (45.0cm3)
H2SO4 + 2NaOH → Na2SO4 + 2H2O. Moles NaOH = 0.2 × 0.045 = 0.009, so acid = 0.0045 mol; volume = 0.0045/0.1 = 0.045 dm3 = 45.0 cm3.
The Avogadro number of 23g of sodium is the same as that of
Answer: D (32g of oxygen molecules.)
23 g of sodium is 1 mole of atoms. 32 g of O2 is also 1 mole of molecules; the others are half a mole.
One of the uses of copper (II) tetraoxosulphate (VI) is
Answer: A (fungicide)
Copper(II) sulphate mixed with lime makes Bordeaux mixture, sprayed on crops to kill fungi.
In the above diagram X can be
Answer: B (a solution of sodium dioxonitrate (III) and ammonium chloride)
Nitrogen is made in the laboratory by warming sodium dinitrate(III) (NaNO2) with ammonium chloride; the gas is collected over water.
Which of the following is a polysaccharide
Answer: C (starch)
Starch is a long chain of glucose units; the others are single sugars (monosaccharides).
The total pressure of mixture of 80.0g of oxygen gas and 56.0g of nitrogen gas is 1.8 atm. Calculate the partial pressure of oxygen gas in the mixture [O=16, N=14]
Answer: A (1.0 atm)
O2: 80/32 = 2.5 mol; N2: 56/28 = 2 mol. Mole fraction of O2 = 2.5/4.5, so p = 2.5/4.5 × 1.8 = 1.0 atm.
The graph below illustrates the pH changes for the titration of a
Answer: B (strong acid versus strong base)
The pH starts low (about 2), ends high (about 12) and jumps steeply around 7 at the end point, which is typical of a strong acid against a strong base.
Coal gas consists of carbon(II)oxide, hydrogen and
Answer: C (methane)
Coal gas from heating coal is mainly hydrogen, methane and carbon(II) oxide.
Which of the following oxide will remain unchanged when heated in hydrogen gas?
Answer: C (ZnO)
Hydrogen reduces oxides of less reactive metals such as iron, copper and lead, but zinc is too reactive, so ZnO is left unchanged.
The bonding that does not involve the formation of a new substance is
Answer: B (metallic)
Metallic bonding holds atoms of the same metal together in a sea of electrons; it does not combine different elements into a compound.