JAMB Past Questions and Answers - Page 1600

7,996.

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.

7,997.

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.

7,998.

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

7,999.

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

7,000.

9.8g of solid potassium chlorate (KCIO3) were added to 40 cm3 of water and heated to dissolve all the solid. As he solution cooled, crystals of potassium chlorate started forming at 60°C. The solubility of potassium chlorate at 66°C is therefore?

A.

24.5 mole per dm3

B.

0.2 mole per dm3

C.

10.0 mole per dm3

D.

20.0 mole per dm3

E.

2.0 mole per dm3

Correct answer is E

9.8 gms KCIO3 dissolves in 40 cm3 of H.
In 100 cc we have (9.8)/(40) x (100)/(1) = 24.5 gm KCIO3

In 1000 cc we have 10 x 24.5
or 245 gms of KCIO3.
But mol wt of KCIO3 is 122.5
Solubility of KCIO3 is (245)/(122.5) = 2 moles per dm3 (E)