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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 chemical equation for the reaction is:
Observation 1: A bright yellow/orange flame is produced during the reaction.
Observation 2: The formation of white solid sodium oxide occurs, which may appear as smoke or powder.
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 in magnesium oxide. Magnesium oxide has a higher charge density due to the +2 charge of magnesium compared to the +1 charge of sodium, resulting in stronger electrostatic attractions between ions. This leads 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 (SiO2) has a giant covalent structure, characterized by a network of strong covalent bonds between silicon and oxygen atoms. This requires a significant amount of energy to break these bonds, resulting in a very high melting point. In contrast, phosphorus pentoxide (P4O10) does not have such a structure and exhibits weaker intermolecular forces, which contribute to its lower melting point.
Step 5
Describe a method for determining the melting point of the sample. State how the result obtained could be used to evaluate its purity.
Answer
- Method: Use a melting point apparatus or capillary tube method. Place a small sample of the phosphorus oxide in a capillary tube and heat it slowly while monitoring the temperature.
- Evaluation of Purity: The observed melting point should match the known melting point (573 K). A sharp melting point indicates high purity, while a broad range would suggest impurities.