Chemistry questions and answers

Chemistry Questions and Answers

Learn more about the properties, composition, and structure of substances (elements and compounds) with these Chemistry questions and answers. This Test can be used by students preparing for Chemistry in JAMB, WAEC, NECO or Post UTME.

2,771.

When air is compressed?

A.

its density decreases

B.

it solidifies

C.

its temperature decreases

D.

its temperature increases

E.

its temperature remains unchanged

Correct answer is D

Compressed air is a gas, or a combination of gases, that has been put under greater pressure than the air in the general environment.

When you pressurize a gas by compressing it into a container, you're putting all those molecules into a smaller volume of space and you're adding potential energy by the compression.

Gay Lussac's Law - states that the pressure of a given amount of gas held at constant volume is directly proportional to the Kelvin temperature. 

2,772.

If an organic compound decolorizes bromine water then the compound is?

A.

saturated

B.

supersaturated

C.

unsaturated

D.

a solid

E.

protonated

Correct answer is C

No explanation has been provided for this answer.

2,773.

When sodium nitrate dissolves in water, ∆H is positive. This means that?

A.

the reaction is catalysed

B.

the reaction is complete

C.

the reaction is exothermic

D.

the reaction is endthermic

E.

sodium nitrate is highly soluble in water

Correct answer is D

No explanation has been provided for this answer.

2,774.

Na2CO3 + 2HCI → 2NaCI + H2O + CO2. Using the above equation, what volume of carbondioxide, measured at s.t.p is liberated when 53g of sodium carbonate is dissolved in hydrochloric acid?
(1 mole of gas occupies 22.4 dm3 at s.t.p)
(Na = 23, C = 12, O = 16)

A.

44.8 dm3

B.

11.2 dm3

C.

100.1 dm3

D.

3.0 dm3

E.

22.4 dm3

Correct answer is B

Na2CO3 + 2HCI → 2NaCI +H2O + CO2
53 gm Na2CO3 will therefore liberate (22.4)/(106) x (53)/(1) = 11.2 dm3

2,775.

100 cm3 of oxygen is made to react with 50 cm 3 of hydrogen, and the whole reaction mixture was then passed through anhydrous calcium chloride. What is the volume of gas left?

A.

5 cm3

B.

25 cm3

C.

50 cm3

D.

75 cm3

E.

100 cm3

Correct answer is D

2H2 + O2 → 2H2O
2V3 1V3 2V
50cm 100 —
50cm 25cm3 50cm3
Volume of gas left = (100 - 25)cm3 of O2 = 75 cm3 of O2