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Questions 5.3.2(b)

Write the formula and name of each of the products of dehydration Solid G, Gas J, Gas L, Solid M.
Write a complete equation for each of the dehydration reactions (b) to (e). Part (a) is already done below as an example. CuSO₄.5H₂O(s) H₂SO₄(l) CuSO₄(s) + 5H₂O(l)
Identify what looks like white fumes in Figure 5.3.2(b), and explain why it is so thick.
As shown in Figure 5.3.2(c) and the video, a relatively small amount of cane sugar produces a "large quantity" of black solid. Suggest an explanation for this.
Explain why concentrated sulphuric (VI) acid is highly corrosive.
Prepare a brief summary of the oxidation and dehydrating properties of concentrated sulphuric (VI) acid.

Answers to Questions 5.3.2(b)

Solid G: C, carbon; Gas J: C₂H₄, ethene; Gas L: CO, carbon (II) oxide; Solid M: C, carbon.
(a) Done as an example
(b) C₂H₅OH(l) H₂SO₄(l) H₂O(l) + C₂H₄(g)
(c) C₁₂H₂₂O₁₁ H₂SO₄(l) 12C(s) + 11H₂O(l)
(d) HCOOH(l) H₂SO₄(l) H₂O(l) + CO(g)
(e) _nC₆H₁₀O₅(s) H₂SO₄(l) 6nC(s) + 5nH₂O(l)

This is water vapour. It is thick because it is produced in large quantities as shown in equation 2(c), and the heat generated vapourizes it.
The black solid is carbon. Removal of elements of water causes the carbon atoms in cane sugar to move further apart, so the solid becomes porous and occupies a much bigger volume.
Concentrated sulphuric (VI) acid is highly corrosive due to its combined oxidizing and dehydrating properties.
Concentrated sulphuric (VI) acid
Oxidation
Hot concentrated sulphuric acid oxidizes non-metals to their oxides, and it is itself reduces to sulphur (IV) oxide (SO₂) and water (H2O).
S(s) + 2H₂SO₄(l) → 2H₂O(l) + 3SO₂(g)
C(s) + 2H₂SO₄(l) → 2H₂O(l) + 2SO₂(g) + CO₂(g)
It oxidies metals to metal sulphates, and is itself reduced to sulphur (IV) oxide and water.
Mg(s) + 2H₂SO₄(l) → MgSO₄(aq) + 2H₂O(l) + SO₂(g)
Cu(s) + 2H₂SO₄(l) → CuSO₄(aq) + 2H₂O(l) + SO₂(g)
Generally: Metal + Concentrated sulphuric (VI) acid → Metal sulphate + Sulphur (IV) oxide + Water
Non-metal + Concentrated sulphuric (VI) acid → Non-metal oxide + Sulphur (IV oxide + Water

Dehydration High affinity for elements of water, hence a strong dehydrating agent.
Examples
Cane sugar (C₁₂H₂₂O₁₁): C₁₂H₂₂O₁₁ H₂SO₄(l) → 12C(s) + 11H₂O(l)
Hydrated copper (II) sulphate: (CuSO₄.5H₂O): CuSO₄.5H₂O H₂SO₄(l) → CuSO₄(s) + 5H₂O(l)
Ethanol: (C₂H₅OH) C₂H₅OH(l) H₂SO₄(l) → H₂O(l) + C₂H₄(g)
Methanoic acid (HCOOH): HCOOH(l) H₂SO₄(l) → H₂O(l) + CO(g)
Wood or paper (-C₆H₁₀O₅-)_n: nC₆H₁₀O₅(s) H₂SO₄(l) → 6nC(s) + 5nH₂O(l)
The acid itself remains intact as H₂SO₄.
The acid is highly corrosive due to its combined oxidizing and dehydrating properties.