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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
Step 2
Step 3
Explain the increase in melting point from sodium oxide to magnesium oxide.
Answer
Magnesium oxide (MgO) has a higher melting point than sodium oxide (Na2O) due to stronger ionic bonds formed between Mg2+ and O2- ions compared to the bonds between Na+ and O2- ions. The greater charge density of magnesium leads to stronger electrostatic attractions and a more stable lattice structure.
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, which requires a large amount of energy to break the strong covalent bonds. In contrast, phosphorus pentoxide (P4O10) has a molecular structure, which consists of weaker van der Waals forces between the molecules. Therefore, SiO2 has a significantly higher melting point compared to P4O10.
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:
- Prepare a sample of the phosphorus oxide and place it in a capillary tube.
- Use a melting point apparatus to gradually heat the sample.
- Record the temperature at which the sample starts to melt and finishes melting.
Evaluation of Purity:
The observed melting point can be compared to the known melting point of pure phosphorus oxide. A sharp melting point close to the expected value indicates high purity, while a broad melting range or deviation suggests impurities may be present.