This question is about Period 3 elements and their compounds - AQA - A-Level Chemistry - Question 5 - 2022 - Paper 1
Question 5
This question is about Period 3 elements and their compounds.
0 5 . 1 Which is not a correct statement about magnesium hydroxide?
Tick (✓) one box.
It is used to ... show full transcript
Worked Solution & Example Answer:This question is about Period 3 elements and their compounds - AQA - A-Level Chemistry - Question 5 - 2022 - Paper 1
Step 1
Which is not a correct statement about magnesium hydroxide?
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Answer
The statement that is not correct about magnesium hydroxide is:
It forms a solution with pH = 14 at 25 °C.
Magnesium hydroxide is a weak base, and while it does neutralize stomach acid, it does not produce such a highly basic solution.
Step 2
Give an equation for the reaction of aluminium oxide with sulfuric acid.
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Answer
The reaction of aluminium oxide (Al₂O₃) with sulfuric acid (H₂SO₄) can be represented as:
Al2O3+3H2SO4→2Al2(SO4)3+3H2O
Step 3
Identify a reagent or test that could be used to distinguish between aqueous solutions of sulfur dioxide and sulfur trioxide.
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Answer
A suitable reagent to distinguish between sulfur dioxide (SO₂) and sulfur trioxide (SO₃) is:
Universal indicator.
Observation with sulfur dioxide solution: The solution will show a slightly acidic pH (around 3).
Observation with sulfur trioxide solution: The solution will turn red indicating a more acidic pH (around 1-2).
Step 4
Give the formula of the species responsible for this peak.
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Answer
The formula of the species responsible for the peak at z = 124 in the mass spectrum of phosphorus is:
P₃.
Step 5
Give an equation for the reaction of phosphorus(V) oxide with sodium hydroxide solution.
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Answer
The reaction of phosphorus(V) oxide (P₂O₅) with sodium hydroxide (NaOH) can be represented as:
P2O5+2NaOH→2NaH2PO4
Step 6
Draw the displayed formula of the molecule formed.
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Answer
The displayed formula for the molecule formed when phosphorus(V) oxide reacts with water (H₂O) produces phosphoric acid (H₃PO₄):
O
||
H₂O - P - OH
|
OH
This representation showcases all bonds around the phosphorus atom.
Step 7
Explain why the melting points of these substances are different.
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Answer
The melting points of sodium chloride, chlorine, and hydrogen chloride differ due to their varying molecular structures and types of bonding:
Sodium chloride (NaCl): It has a high melting point (1074 K) because it forms ionic bonds in a strong lattice structure, requiring significant energy to break these bonds.
Chlorine (Cl₂): Chlorine is a diatomic molecule with weak Van der Waals forces between molecules, resulting in a low melting point (172 K).
Hydrogen chloride (HCl): HCl has polar covalent bonds and exhibits dipole-dipole interactions, leading to a melting point of 158 K, higher than chlorine but lower than sodium chloride.
In summary, ionic bonds in NaCl lead to high melting points, while weak intermolecular forces in Cl₂ and polar interactions in HCl contribute to their lower melting points.
