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a) Figure 5 shows the structure of a molecule of compound S - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2023 - Paper 1
Question 6
a) Figure 5 shows the structure of a molecule of compound S. (i) Use Figure 5 to deduce the empirical formula of compound S. (ii) The melting points of three sam... show full transcript
Worked Solution & Example Answer:a) Figure 5 shows the structure of a molecule of compound S - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2023 - Paper 1
Step 1
(i) Use Figure 5 to deduce the empirical formula of compound S.
Answer
To find the empirical formula of compound S, first identify the number of each type of atom in the molecule from Figure 5. The structure reveals 6 Carbon (C) atoms, 10 Hydrogen (H) atoms, and 1 Oxygen (O) atom. Therefore, the empirical formula can be deduced as C6H10O. To express it in simplest ratio, we divide each subscript by the greatest common divisor which remains C6H10O, as they cannot be further simplified.
Step 2
(ii) State whether each of these samples, A, B and C, is pure or impure and justify your answers using the information in Figure 6.
Answer
The melting point of sample A is listed as 160-164 °C, sample B is 166 °C, and sample C is 163-165 °C.
- Sample A is considered impure because its melting point range indicates that it contains more than one substance, as pure substances have a specific melting point.
- Sample B is pure because it has a specific melting point of 166 °C, suggesting only one component is present.
- Sample C is also impure, as it has a melting point range similar to that of sample A, which indicates that it too is not a single pure substance.
Step 3
Step 4
Explain this difference in boiling points in terms of the structure and bonding of sodium chloride and water and how this difference is used to choose a method to separate sodium chloride solution into pure, dry sodium chloride and pure water.
Answer
Sodium chloride (NaCl) and water (H2O) have significantly different boiling points due to their distinct structures and bonding.
Sodium Chloride: Sodium chloride has an ionic structure with strong electrostatic forces holding Na+ and Cl- ions together in a lattice arrangement. This structure requires a high amount of energy to break the ionic bonds, which contributes to its high boiling point of 1465 °C.
Water: On the other hand, water consists of polar covalent bonds between hydrogen and oxygen. The hydrogen bonds present in water are weaker compared to ionic bonds; thus, it has a much lower boiling point of 100 °C.
Separation Method: The higher boiling point of sodium chloride than that of water allows for the method of distillation or evaporation to be applied. When a saltwater solution is heated, water vaporizes first, leaving behind solid sodium chloride. This allows for the effective separation of dry sodium chloride and pure water from the solution.