Electrochemistry

The equation for a reaction of $\text{KClO}_3$ is shown.

$$4\text{KClO}_3 \rightarrow \text{KCl} + 3\text{KClO}_4$$

Which row is correct?

Options

Copper reacts with nitric acid under certain conditions. The products are copper(II) nitrate, water and an oxide of nitrogen.

$3\text{ mol}$ of copper reacts with exactly $8\text{ mol}$ of nitric acid.

What is the oxidation state of nitrogen in the oxide produced?

Options

A   +1
B   +2
C   +3
D   +4

$\text{ICl}_3$ reacts with water in a redox reaction.

$$v\text{ICl}_3 + w\text{H}_2\text{O} \rightarrow x\text{HCl} + y\text{HI} + z\text{HIO}_3 + z\text{HClO}_3$$

What are the numbers $v$, $x$ and $z$ in the correctly balanced equation?

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The structure of the testosterone molecule is shown.

Which statements are correct?

1. Carbon atoms C1 and C2 can be oxidised with acidified $\text{K}_2\text{Cr}_2\text{O}_7$.
2. There are fewer than 27 hydrogen atoms in one testosterone molecule.
3. There are six chiral carbon atoms in one testosterone molecule.

Options

A   1 only
B   2 and 3
C   2 only
D   3 only

‘Red lead’ is a red pigment with the formula $\text{Pb}_3\text{O}_4$. Every formula unit of ‘red lead’ is the same.

Each formula unit contains three lead ions and four oxide ions. Lead has two different oxidation states in ‘red lead’.

What are the oxidation states of lead in ‘red lead’?

Options

A   +1 and +2
B   +1 and +3
C   +2 and +4
D   +2 and +6

Sodium bromide is warmed with concentrated sulfuric acid.

Which row describes the change in the oxidation number of the sulfur and the role of the bromide ions in the reaction?

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Chromium is present in compound X.

• Two moles of compound X react with exactly 3 moles of silicon.
• The only products of this reaction are 4 moles of chromium and 3 moles of a silicon compound in which the oxidation state of the silicon is +4.
• Chromium and silicon are the only elements that change their oxidation states in this reaction.

What could be the identity of compound X?

Options

A   $\text{Cr}_2\text{O}_3$
B   $\text{Cr}_2\text{H}_6$
C   $\text{Cr}_2\text{H}_4$
D   $\text{Cr}_2\text{O}_4$

In this question, the average oxidation state of sulfur in S₂O₃²⁻ and sulfur in S₂O₄²⁻ should be used.

In which reaction does the underlined element have the largest increase in oxidation state?

Options

A   3CrO₄³⁻(aq) + 8H⁺(aq) → 2CrO₄²⁻(aq) + Cr³⁺(aq) + 4H₂O(l)
B   2NO₂(g) + H₂O(l) → HNO₃(aq) + HNO₂(aq)
C   S₂O₃²⁻(aq) + 2H⁺(aq) → S(s) + SO₂(g) + H₂O(l)
D   2S₂O₄²⁻(aq) + H₂O(l) → S₂O₃²⁻(aq) + 2HSO₃⁻(aq)

When K₂MnO₄ reacts with concentrated hydrochloric acid, the products include chlorine molecules and MnCl₂. All of the manganese atoms are reduced to MnCl₂.

Both Mn and Cl change their oxidation numbers during the reaction. No other element is oxidised or reduced.

Using these changes in oxidation number, how many moles of chlorine will be produced when 1.0 mol of K₂MnO₄ reacts with an excess of hydrochloric acid?

Options

A   2.0 mol
B   2.5 mol
C   3.0 mol
D   4.0 mol

Sulfite ions, $\text{SO}_3^{2-}$, react separately with zinc and with manganese dioxide.

$a, b, c, d, w, x, y$ and $z$ are all whole numbers.

$$a\text{SO}_3^{2-}(\text{aq}) + b\text{H}_2\text{O}(\text{l}) + \text{Zn}(\text{s}) \rightarrow \text{Zn}^{2+}(\text{aq}) + c\text{OH}^-(\text{aq}) + d\text{S}_2\text{O}_4^{2-}(\text{aq})$$ $$\text{MnO}_2(\text{s}) + w\text{SO}_3^{2-}(\text{aq}) + x\text{H}^+(\text{aq}) \rightarrow \text{Mn}^{2+}(\text{aq}) + y\text{S}_2\text{O}_6^{2-}(\text{aq}) + z\text{H}_2\text{O}(\text{l})$$

Which numbers are correct for $a, b, w$ and $x$?

Options