Question 626:

• JAMB 1990

Which of the following is a physical change?

A. The bubbling of chlorine into water
B. The bubbling of chlorine into a jar contanining hydrogen
C. The dissolution of sodium chloride in water
D. The passing of steam over heated iron

Question 627:

• JAMB 1990

In a reaction: \(SnO_{2} + 2C → Sn + 2CO\) the mass of coke containing 80% carbon required to reduce 0.302 kg of pure tin oxide is?
(Sn - 119, O - 16, C - 12).

A. 0.40 kg
B. 0.20 kg
C. 0.06 kg
D. 0.04 kg

Question 628:

• JAMB 1990

Cr₂O₇ + 6Fe²⁺ + 14H⁺ → 2Cr³⁺ +6Fe³⁺ + 7H₂O. In the above , the oxidation number of chromium changed from?

A. +7 to +3
B. +6 to +3
C. +5 to +3
D. -2 to +3

Question 629:

• JAMB 1990

In the reaction 1O^-₃ + 5l^- + 6H⁺ → 31₂ + 3H₂O, the oxidizing agent is?

A. H⁺
B. L^-
C. 1O^-
D. L₂

Question 630:

• JAMB 1990

Fe\(_2\)O\(_{3(s)}\) + 2Al\(_{(s)}\) → Al\(_2\)O\(_3\) + 2Fe\(_{(s)}\). If the heats of formation of Al\(_2\)O\(_3\) and Fe\(_2\)O\(_3\) are - 1670 kJmol\(^{-1}\) and - 822 kJmol\(^{-1}\) respectively, the enthalpy change in kJ for the reaction is ?

A. +2492
B. +848
C. -848
D. -2492