Some Chemistry TYS MCQ Questions
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1997
1) In an experiment 4.0 cm^3 of 1.0mol/dm^3 aq. copper(II) sulphate was mixed with 8 cm^3 of 1.0mol/dm^3 aq. sodium carbonate.
What did the reaction vessel contain when the reaction was complete?
A: a colourless solution only
B: a green ppt and a blue solution (ppt: precipitate)
C: a green ppt and a colourless solution
D: a white precipitate and a blue solution
Answer is C. How did they get the green ppt?
1998
2) All ammonium salts on heating with sodium hydroxide produce ammonia gas. From which ammonium salt can the greatest mass of ammonia be obtained?
A: 0.5 mol (NH4)3 PO4
B: 0.5 mol (NH4)2 SO4
C: 1.0 mol NH4 Cl
D: 1.0 mol NH4 NO3
Answer is A but I get B?
3) Which statement about graphite is not correct?
A: It burns to from carbon dioxide.
B: It is a carbon compound.
C: It is a macromolecule
D: It is used as a lubricant.
Answer is B but I get A? (C and D is confirm out but graphite burns to form CO2?)
1999
4) What do both an atom and an ion of the isotope of sodium, Na, contain?
A: 11 electrons
B: 12 neutrons
C: 23 neturons
D: 23 protons
Answer is B but I get A? (Why is it 12 neutrons when it is an isotope? Although I know now that A should be wrong as the atom and ion should have different electrons but B should also be incorrect?)
2000
5) An excess of sodium hydroxide is added to an aqueous solution of salt X and boiled. Ammonia gas is only given off after aluminium foil is added to the solution. What could be X?
A: ammonium chloride
B: ammonium nitrate
C: sodium chloride
D: sodium nitrate
Ans is D but i got A? Why is it sodium nitrate?
2002
6) If a strip of magnesium is dropped into excess hydrochloric acid an exothermic reaction occurs. The rate of reaction increases during the first few seconds because:
A: the amount of magnesium is decreasing
B: the magnesium is acting as a catalyst
C: the solution is becoming hotter
D: the surface area of the magnesium is increasing.
Answer is C but I get A. What has the solution getting hotter got to do with increase in rate of reaction? oo
7) Aluminium is extracted from purified bauxite by electrolysis but iron is extracted from haematite by reduction with coke.
Why is iron not extracted by electrolysis?
A: Haematite needs to be purified but bauxite does not
B: Iron is less reactive than aluminium
C: Reduction with coke is cheaper than electrolysis
D: Redcution with coke gives a purer product than electrolysis
Answer is C and I find the answer very weak. Isn't it supposed to be B? Also I thought that cost of substances for chemistry should be put to the least priority?
2003
8) Which of the following, when added to water, makes a solution that is a good conductor of electricity?
A: calcium carbonate
B: copper
C: ethanol
D: sodium hydroxide
Answer is D but i get A?
2004
9) A vegetable oil is polyunsaturated.Which statement about this oil is correct?
A: It has double bonds between carbon and hydrogen atoms
B: It reacts with hydrogen to form a solid compound.
C: It reacts with steam to form margarine
D: It turns aq. bromine from colourless to brown.
Answer is B but i Get A?
2005
10) Which two gases each change the colour of damp red litmus paper?
A: ammonia and chlorine
B: ammonia and hydrongen chloride
C: carbon dioxide and chlorine
D: carbon dioxide and sulphur dioxide
Answer is A but i get A?
11) One mole of compound X gives three moles of ions in aqueous solution. X reacts with ammonium carbonate to give an acidic gas.
What is compound X?
A: calcium hydroxide
B: ethanoic acid
C: sodium hydroxide
D: sulphuric acid
Answer is D but i get A?
12) Which gas is not produced when hydrocarbons are burnt in the internal combustion engine?
A: carbon dioxide
B; carbon monoxide
C: hydrogen
D: nitrogen oxides
Answer is C but i get A? I thought carbon dioxide is not produced also?
2006
13) Which substance reacts with water to form a soluble compound and an insoluble gas?
A ammonium sulphate
B caesium
C calcium carbonate
D copper
Answer is B but i get C?
14) To reduce atmospheric pollution, the waste gases from a coal-burning power station are passed through powdered calcium carbonate. Which waste gas will not be removed by powered calcium carbonate?
A Carbon monoxide
B nitrogen dioxide
C phosphorus (V) oxide
D sulphur dioxide
Answer is C but i get A?
2007
15) In an electrolysis experiment, the same amount of charge deposited 16g of copper and 6g of titanium. What was the charge on the titanium ion?
A: 1+ B: 2+ C: 3+ D: 4+
Answer is D and I totally dont know how to get the answer.
Help will be kindly appreciated, Thank you all.
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Other forumners & students, and Mod TinTin, pls feel free to reply to Peoplethinkimsarcastic'squestions in detail.
Very brief comments & hints.
Q1. Determine limiting reactant.
Q2. Compare no. of moles of NH4+ ions present for the 4 options.
Q3. It's an allotrope of C, not compound. In excess oxygen, you get CO2. Otherwise, CO.
Q4. The proper definition of isotopes (90% of students and even secondary school teachers get it wrong) is "Isotopes of elements have atoms with the same no. of protons but different no. of neutrons", and not "isotopes are atoms..."
Q5. Cation can't be NH4+, or else you get NH3 gas immediately upon adding OH-(aq). Nitrate ion is first reduced (by Al metal) to NH4+ ion, which combines with OH- ion to give NH3(g) and H2O(l).
Q6. Increase in temperature results in greater % of reactant molecules having energy equals or exceeding activation energy required for reaction, hence rate of reaction increases.
Q7. B is true enough to make C correct. C answers the question more directly.
Q8. CaCO3 is insoluble.
Q9. Unsaturated means it has at least one (or more) double or triple bonds between adjacent C atoms.
Q10. "Answer is A but i get A?" Perhaps *chemistry* isn't the issue here? Exam stress can be counteracted by relaxation...
Q11. CO2 is a non-metal oxide and hence an acidic gas. CO2(g) + H2O(l) <---> H2CO3(aq).
Q12. The only possible products of burning hydrocarbons is carbon monoxide, carbon dioxide, water.
Q13. Grp I (Alkali Metals) metals react with water to form metal hydroxides and hydrogen gas, which is non-polar, doesn't ionize (eg. like HCl does), and hence insoluble in water.
Q14. Non-metal oxides are acidic and will react with the carbonate base. Carbon monoxide is a reducing agent (it wants to be oxidized to the more stable CO2 form), and has no reaction with carbonates.
Q15. Write the reduction half-equations at the cathode, for both metals. Calculate the no. of electrons transferred. Work with algebra ("Let the oxidation state of the Ti cation be +X") if you prefer. If every 1 mole of the titanium required 4 moles of electrons to reduce it to Ti atoms (ie. titanium metal), the oxidation state must be +4 (ie. the charge must be 4+).
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Originally posted by Peoplethinkimsarcastic:
1997
1) In an experiment 4.0 cm^3 of 1.0mol/dm^3 aq. copper(II) sulphate was mixed with 8 cm^3 of 1.0mol/dm^3 aq. sodium carbonate.
What did the reaction vessel contain when the reaction was complete?
A: a colourless solution only
B: a green ppt and a blue solution (ppt: precipitate)
C: a green ppt and a colourless solution
D: a white precipitate and a blue solution
Answer is C. How did they get the green ppt?
CuSO4 (aq) + Na2CO3 (aq) ---> CuCO3 (s) + Na2SO4 (aq) + some excess unreacted sodium carbonate
No. of mol CuSO4 ---> 0.004*1.0 = 0.004 mol
No. of mol Na2CO3 ---> 0.008*1.0 = 0.008 molHence, copper (II) sulphate is the limiting reagent (meaning it will be fully reacted), so the resulting solution will not have any blue colour.
The ppt, copper (II) carbonate, formed is green in colour, while sodium sulphate is colourless.
Therefore, the result will be a green ppt in a colourless solution.
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Originally posted by Peoplethinkimsarcastic:
1998
2) All ammonium salts on heating with sodium hydroxide produce ammonia gas. From which ammonium salt can the greatest mass of ammonia be obtained?
A: 0.5 mol (NH4)3 PO4
B: 0.5 mol (NH4)2 SO4
C: 1.0 mol NH4 Cl
D: 1.0 mol NH4 NO3
Answer is A but I get B?
A:
(NH4)3PO4 + 3NaOH ---> Na3PO4 + 3H2O + 3NH3
No. of mol NH3 produced ---> 0.5*3 = 1.5 mol
B:
(NH4)2SO4 + 2NaOH ---> Na2SO4 + 2H2O + 2NH3
No. of mol NH3 produced ---> 0.5*2 = 1 mol
C:
NH4Cl + NaOH ---> NaCl + H2O + NH3
No. of mol NH3 produced ---> 1.0 mol
D:
NH4NO3 + NaOH ---> NaNO3 + H2O + NH3
No. of mol NH3 produced ---> 1.0 mol
Since highest no. of mol NH3 produced is A, the mass would also be the highest.
So, A is the answer. -
Originally posted by Peoplethinkimsarcastic:
3) Which statement about graphite is not correct?
A: It burns to from carbon dioxide.
B: It is a carbon compound.
C: It is a macromolecule
D: It is used as a lubricant.
Answer is B but I get A? (C and D is confirm out but graphite burns to form CO2?)
Graphite is an allotrope of carbon, meaning to say it consists of only carbon atoms. (Allotropes are different forms of the same element)
Combustion of graphite produces carbon dioxide.
C + O2 ---> CO2
Graphite is an element, not a compound. (Compound is a substance consisting of 2 or more different elements chemically bonded together)
Therefore, B is the answer.
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Originally posted by Peoplethinkimsarcastic:
1999
4) What do both an atom and an ion of the isotope of sodium, Na, contain?
A: 11 electrons
B: 12 neutrons
C: 23 neturons
D: 23 protons
Answer is B but I get A? (Why is it 12 neutrons when it is an isotope? Although I know now that A should be wrong as the atom and ion should have different electrons but B should also be incorrect?)
Hmm, I think that B is incorrect too as a sodium atom contains 11p, 11e, 12n while an ion of the isotope of sodium contains 11p, 10e and a number of neutrons which cannot be 12 as it is an isotope.
EDIT: I think I get what the question is trying to say.
"What do both an atom of the isotope of sodium and an ion of the isotope of sodium, Na, contain?"
In this case, since both are isotopes, they should contain the same number of neutrons. Hence, B is the answer.
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Originally posted by Peoplethinkimsarcastic:
2000
5) An excess of sodium hydroxide is added to an aqueous solution of salt X and boiled. Ammonia gas is only given off after aluminium foil is added to the solution. What could be X?
A: ammonium chloride
B: ammonium nitrate
C: sodium chloride
D: sodium nitrate
Ans is D but i got A? Why is it sodium nitrate?
Since ammonia gas is given off when solution is heated with aluminium foil, nitrate ions are present.
As ammonia gas is given off only after aluminium foil is added, X cannot contain ammonium ions as this would mean that X is an ammonium salt.
When an ammonium salt is heated with an alkali (in this case NaOH), ammonia gas will be immediately given off.Hence, the best possible answer is D.
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Originally posted by Peoplethinkimsarcastic:
2002
6) If a strip of magnesium is dropped into excess hydrochloric acid an exothermic reaction occurs. The rate of reaction increases during the first few seconds because:
A: the amount of magnesium is decreasing
B: the magnesium is acting as a catalyst
C: the solution is becoming hotter
D: the surface area of the magnesium is increasing.
Answer is C but I get A. What has the solution getting hotter got to do with increase in rate of reaction? oo
When the amount of magnesium decreases, the surface area of magnesium in contact with the acid does not increase, so this does not contribute to a faster reaction.
A and D is out.Magnesium is not a catalyst, it is a reactant.
B is out.Since this is an exothermic reaction, temperature of solution increases.
A higher temperature results in a faster rate of reaction.
C is the answer. -
Originally posted by Peoplethinkimsarcastic:
7) Aluminium is extracted from purified bauxite by electrolysis but iron is extracted from haematite by reduction with coke.
Why is iron not extracted by electrolysis?
A: Haematite needs to be purified but bauxite does not
B: Iron is less reactive than aluminium
C: Reduction with coke is cheaper than electrolysis
D: Redcution with coke gives a purer product than electrolysis
Answer is C and I find the answer very weak. Isn't it supposed to be B? Also I thought that cost of substances for chemistry should be put to the least priority?
Iron, being less reactive than aluminium, can be extracted by reduction with coke.
However, this is not a good reason not to use electrolysis.
The main reason is still about the cost.
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Originally posted by Peoplethinkimsarcastic:
2003
8) Which of the following, when added to water, makes a solution that is a good conductor of electricity?
A: calcium carbonate
B: copper
C: ethanol
D: sodium hydroxide
Answer is D but i get A?
Calcium carbonate is insoluble in water.
The only carbonates which are soluble in water are sodium, potassium and ammonium.Sodium hydroxide is soluble in water. Its ions dissociate in water. Due to the presence of these ions, electrical conductivity of the solution is increased.
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Originally posted by Peoplethinkimsarcastic:
2004
9) A vegetable oil is polyunsaturated.Which statement about this oil is correct?
A: It has double bonds between carbon and hydrogen atoms
B: It reacts with hydrogen to form a solid compound.
C: It reacts with steam to form margarine
D: It turns aq. bromine from colourless to brown.
Answer is B but i Get A?
The term 'polyunsaturated' means that vegetable oil contains C=C bonds. (not C=H bonds)
A hydrogen atom can only form a single bond as it only needs to share 1 electron.
So, A is incorrect.Vegetable oil turns aq. bromine from brown to colourless.
So, C is wrong.Vegetable oil reacts with hydrogen (not steam) to form margarine, a solid compound.
So, B is correct. -
Originally posted by Peoplethinkimsarcastic:
2005
10) Which two gases each change the colour of damp red litmus paper?
A: ammonia and chlorine
B: ammonia and hydrongen chloride
C: carbon dioxide and chlorine
D: carbon dioxide and sulphur dioxide
Answer is A but i get A?
U got type wrongly? Ur answer is A and it's correct.
Ammonia gas reacts water to form ammonium hydroxide, an alkaline substance, which turns red litmus paper blue.
Chlorine bleaches damp red litmus paper.B is wrong as hydrogen chloride gas reacts with water to form hydrochloric acid, which turns litmus papers red.
C is wrong as carbon dioxide reacts with water to form carbonic acid, which also turns litmus papers red. Hence, D is also wrong.
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Originally posted by Peoplethinkimsarcastic:
11) One mole of compound X gives three moles of ions in aqueous solution. X reacts with ammonium carbonate to give an acidic gas.
What is compound X?
A: calcium hydroxide
B: ethanoic acid
C: sodium hydroxide
D: sulphuric acid
Answer is D but i get A?
Acidic gas formed indicates that X is an acid as acid reacts with carbonates to form a salt, water and carbon dioxide, an acidic gas.
A and C is out.Ethanoic acid, CH3COOH, ionises in water to form H+ and CH3COO- ions. Only 2 moles of ions are produced.
B is out.Sulphuric acid, H2SO4, ionises in water to form 2H+ and SO4 2- ions. 3 moles of ions are produced.
Hence, D is the answer. -
Originally posted by Peoplethinkimsarcastic:
12) Which gas is not produced when hydrocarbons are burnt in the internal combustion engine?
A: carbon dioxide
B; carbon monoxide
C: hydrogen
D: nitrogen oxides
Answer is C but i get A? I thought carbon dioxide is not produced also?
Carbon dioxide is formed during complete combustion of hydrocarbons.
Carbon monoxide is formed during incomplete combustion of hydrocarbons.
Nitrogen oxides are formed when oxygen reacts with nitrogen gas.
Hydrogen gas is not formed.
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Originally posted by Peoplethinkimsarcastic:
2006
13) Which substance reacts with water to form a soluble compound and an insoluble gas?
A ammonium sulphate
B caesium
C calcium carbonate
D copper
Answer is B but i get C?
Calcium carbonate and copper are insoluble in water.
Ammonium sulphate ionises in water but no gas is formed.
Caesium reacts with water to form caesium hydroxide (soluble compound) and hydrogen gas (insoluble gas).
Hence, B is the answer.
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Originally posted by Peoplethinkimsarcastic:
2007
15) In an electrolysis experiment, the same amount of charge deposited 16g of copper and 6g of titanium. What was the charge on the titanium ion?
A: 1+ B: 2+ C: 3+ D: 4+
Answer is D and I totally dont know how to get the answer.
Reaction at cathode (for copper):
Cu2+ + 2e ---> Cu
16g of Cu ---> 0.25 moles of Cu
0.25 Cu2+ + 0.5e ---> 0.25 Cu
The amount of charge = 0.5e
6g of Ti ---> 0.125 moles of Ti
0.125 Ti (do not know about the charge on Ti yet) + 0.5e ---> 0.125 Ti
Change it to 1 mol of Ti.
Ti (still do not know about the charge) + 4e ---> Ti
Since 4e is needed to displace 1 mole of titanium, the charge on titanium is 4+
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Thanks both of you for your detailed explanations. Most of my doubts have been cleared except Q10.
Q10. "Answer is A but i get A?" Perhaps *chemistry* isn't the issue here? Exam stress can be counteracted by relaxation...
U got type wrongly? Ur answer is A and it's correct.
Ammonia gas reacts water to form ammonium hydroxide, an alkaline substance, which turns red litmus paper blue.
Chlorine bleaches damp red litmus paper.B is wrong as hydrogen chloride gas reacts with water to form hydrochloric acid, which turns litmus papers red.
C is wrong as carbon dioxide reacts with water to form carbonic acid, which also turns litmus papers red. Hence, D is also wrong.
Yup
I have typed wrongly I put D.May I know if sulphuric acid will change the colour of damp red litmus paper?
Also bleaching of the red litmus paper considered colour change? o.o
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Originally posted by Peoplethinkimsarcastic:
Yup
I have typed wrongly I put D.May I know if sulphuric acid will change the colour of damp red litmus paper?
Also bleaching of the red litmus paper considered colour change? o.o
of cos not... its red already... the acidic colour. wad colour u want to change to?
initial colour of paper = red
final colour of paper = white.
have colour change? u tell me... ..
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Okay thanks
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i have a question..
does hydrogen change the colour of a litmus paper?
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Originally posted by YTH:
i have a question..
does hydrogen change the colour of a litmus paper?
neither acidic nor alkaline
so no
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thanks!!
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Is halogen gas neutral? Meaning when it passes through litmus solution, the solution will remain colourless?
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Originally posted by [e].Le-V:
Is halogen gas neutral? Meaning when it passes through litmus solution, the solution will remain colourless?
No. Halogens will react with water.Chlorine gas (for example) dissolves in water to form hypochlorous acid and hydrochloric acid.
Cl2(g) + H2O(l) --> HOCl(aq) + HCl(aq)
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Erm... I know halogens react with water.
But my question is will it change the colour of litmus solution?
Because there is a question:
Excess chlorine gas is bubbled through litmus solution. Which colours are seen when the reactions are complete?
A. Colourless B. Red C. Blue D. Yellow
The answer is A.
Maybe I missed the word 'excess'...? What will happen?