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Figure 5 shows the structure of a molecule of compound S - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2023 - Paper 1
Question 6
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 samples ... show full transcript
Worked Solution & Example Answer:Figure 5 shows the structure of a molecule of compound S - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2023 - Paper 1
Step 1
Use Figure 5 to deduce the empirical formula of compound S.
Answer
To deduce the empirical formula from Figure 5, we first need to count the number of different atoms present in the molecule. In compound S, we have:
- Carbon (C): 6 atoms
- Hydrogen (H): 12 atoms
- Oxygen (O): 1 atom
The empirical formula can be determined by simplifying the ratio of these atoms. The ratio of C:H:O is 6:12:1, which can be simplified to 6:12:1 = 6:12:1 = 6:1:1. Therefore, the empirical formula of compound S is:
C6H12O.
Step 2
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
To determine the purity of the samples A, B, and C based on their melting points:
- Sample A (160-164°C): This sample has a range, thus indicating that it is impure because a pure substance would have a sharp, defined melting point.
- Sample B (166°C): This sample has a specific melting point without a range, indicating that it is likely pure.
- Sample C (163-165°C): Similar to sample A, this sample shows a range, suggesting that it is impure.
In summary, A is impure, B is pure, and C is impure.
Step 3
Calculate the distance the spot of compound S moves if the solvent front has moved by 2.4 cm.
Answer
To calculate the distance the spot of compound S moves, we can use the formula for Rf (retention factor):
Given: Rf = 0.22 and the distance the solvent front has moved = 2.4 cm.
Let x be the distance the spot of compound S moves:
Rearranging gives:
Therefore, the distance the spot of compound S moves is 0.528 cm.
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
The boiling point of sodium chloride (1465°C) is significantly higher than that of water (100°C). This difference can be explained by the types of bonds and structure each substance has:
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Sodium Chloride: This compound has a strong ionic bond due to the electrostatic attraction between the positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). The lattice structure requires a great deal of energy to break these bonds, hence the very high boiling point.
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Water: In comparison, water has polar covalent bonds and exhibits hydrogen bonding, which is relatively weaker than ionic bonds. The lower energy required to break hydrogen bonds results in water's much lower boiling point.
To separate sodium chloride solution into pure components, one can take advantage of these boiling point differences. By heating the solution, water will evaporate at 100°C, leaving behind dry sodium chloride. This separation method relies on the distinct boiling points to ensure that the components are isolated effectively.