Some Chemistry TYS MCQ Questions

Peoplethinkimsarcastic SG

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.

UltimaOnline SG

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+).

wishboy SG

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 mol

Hence, 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.

wishboy SG

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?

(NH4)3PO4 + 3NaOH ---> Na3PO4 + 3H2O + 3NH3

No. of mol NH3 produced ---> 0.5*3 = 1.5 mol

(NH4)2SO4 + 2NaOH ---> Na2SO4 + 2H2O + 2NH3

No. of mol NH3 produced ---> 0.5*2 = 1 mol

NH4Cl + NaOH ---> NaCl + H2O + NH3

No. of mol NH3 produced ---> 1.0 mol

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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.

wishboy SG

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+

Peoplethinkimsarcastic SG

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

arigatoast SG

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... ..

Peoplethinkimsarcastic SG

Okay thanks

YTH SG

i have a question..

does hydrogen change the colour of a litmus paper?