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The elements sodium to sulfur in Period 3 all react with oxygen to form oxides - AQA - A-Level Chemistry - Question 2 - 2018 - Paper 3
Question 2
The elements sodium to sulfur in Period 3 all react with oxygen to form oxides. 1. Give an equation and two observations made for the reaction that occurs when sodi... show full transcript
Worked Solution & Example Answer:The elements sodium to sulfur in Period 3 all react with oxygen to form oxides - AQA - A-Level Chemistry - Question 2 - 2018 - Paper 3
Step 1
Give an equation and two observations made for the reaction that occurs when sodium is heated in oxygen.
Answer
The equation for the reaction when sodium is heated in oxygen is:
Observation 1: A yellow/orange flame is produced during the reaction.
Observation 2: White solid (sodium oxide) is formed as a product.
Step 2
Step 3
Explain the increase in melting point from sodium oxide to magnesium oxide.
Answer
The increase in melting point from sodium oxide (1548 K) to magnesium oxide (3125 K) can be attributed to the stronger ionic bonds present in magnesium oxide. Magnesium ions ( ext{Mg}^{2+}) have a higher charge density compared to sodium ions ( ext{Na}^{+}), resulting in greater electrostatic attraction between Mg and O atoms, leading to a higher melting point.
Step 4
Explain why the melting point of the oxide of silicon is much higher than that of the highest oxide of phosphorus.
Answer
Silicon dioxide ( ext{SiO}_2) has a giant covalent structure, which involves strong covalent bonds extending throughout the structure. In contrast, phosphorus pentoxide ( ext{P}4O{10}) has discrete molecular structures with weaker intermolecular forces. This difference in bonding results in silicon dioxide having a much higher melting point than phosphorus pentoxide.
Step 5
Describe a method for determining the melting point of the highest oxide of phosphorus. State how the result obtained could be used to evaluate its purity.
Answer
To determine the melting point of the highest oxide of phosphorus, one can use a melting point apparatus. Place a small sample of the oxide in a capillary tube and heat it gradually while monitoring the temperature. The melting point is recorded when the sample transitions from solid to liquid.
To evaluate purity, compare the observed melting point with the known melting point of the pure compound. A sharp melting point within a narrow range indicates high purity, while a broader range suggests impurities.