Chemistry Questions & Answers - Free Online Practice

3,141.

Iron galvanized with zinc is cathodically protected from corrosion. This is because?

zinc has a more positive oxidation potential than iron

zinc has less positive oxidation potential than iron

bith have the same oxidation potential

zinc is harder than iron

Correct answer is A

Iron galvanized with zinc is cathodically protected from corrosion because Zinc has a more positive oxidation potential than iron. This means that Zinc will preferentially corrode, acting as a sacrificial anode.

3,142.

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 ?

+2492

+848

-848

-2492

View answer & explanation

Correct answer is C

Heat of formation = Heat of products - Heat of reactants

= - 1670 - (- 822)

= - 1670 + 822

= - 848 kJ

3,143.

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

H⁺

l^-

1O^-

l₂

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

3,144.

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

+7 to +3

+6 to +3

+5 to +3

-2 to +3

View answer & explanation

Correct answer is A

No explanation has been provided for this answer.

3,145.

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).

0.40 kg

0.20 kg

0.06 kg

0.04 kg

View answer & explanation

Correct answer is C

In the reaction: \(SnO_{2} + 2CO\)
From the equation above
2(12 g) carbon = 151 g \(SnO_{2}\)

24 g carbon =151 g \(SnO_{2}\)
= 0.302 kg \(SnO_{2}\) = 24/151g χ 0.0302 kg carbon = 0.048 kg carbon

Mass of coke is required not mass of carbon,so it is (0.048\(\times\)100)\(\div\)80 = 0.06