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Inorganic chemistry and electrochemistry
6 NET Chemistry questions with answers and explanations.
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Which of these has the largest atomic radius?
- 1 Magnesium
- 2 Aluminium
- 3 Silicon
- 4 Sodium
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Correct answer: Sodium
Atomic radius decreases across a period, so sodium, at the left of the third period, is the largest.
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What is the oxidation number of chlorine in HClO4?
- 1 +7
- 2 +5
- 3 +1
- 4 -1
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Correct answer: +7
H is +1 and four O atoms are -8, so Cl must be +7 to make the molecule neutral.
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Electrolysis of concentrated sodium chloride solution (brine) gives chlorine at the anode and:
- 1 Oxygen at the cathode
- 2 Hydrogen and sodium hydroxide
- 3 Sodium metal
- 4 Hydrochloric acid
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Correct answer: Hydrogen and sodium hydroxide
At the cathode, water is reduced to hydrogen and hydroxide ions, which leaves sodium hydroxide in solution.
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A cell reaction is spontaneous when its standard cell potential is:
- 1 Negative
- 2 Zero
- 3 Positive
- 4 Exactly 1 V
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Correct answer: Positive
A positive E cell means a negative change in Gibbs energy, so the reaction is spontaneous.
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What is the electronic configuration of the Fe3+ ion? (Atomic number of iron is 26.)
- 1 [Ar] 3d6
- 2 [Ar] 3d5
- 3 [Ar] 4s2 3d3
- 4 [Ar] 3d3
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Correct answer: [Ar] 3d5
Iron is [Ar] 4s2 3d6. It loses the two 4s electrons and one 3d electron to form Fe3+, leaving 3d5.
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How many unpaired electrons does the Mn2+ ion have? (Atomic number of manganese is 25.)
- 1 3
- 2 4
- 3 5
- 4 7
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Correct answer: 5
Mn2+ is [Ar] 3d5. The five d electrons occupy five orbitals singly, so there are five unpaired electrons.