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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 sampl... 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
Use Figure 5 to deduce the empirical formula of compound S.
Answer
To determine the empirical formula of compound S from its structure in Figure 5, count the number of each type of atom present. Based on the molecular structure, compound S consists of carbon (C), hydrogen (H), and oxygen (O) atoms. The empirical formula is represented as CxHyOz, where x, y, and z are the respective counts of carbon, hydrogen, and oxygen atoms in the simplest whole number ratio. If, for instance, there are 6 carbons, 12 hydrogens, and 1 oxygen, the empirical formula would be C6H12O or CH2O when reduced to the simplest form.
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 if sample A, B, and C are pure substances, consider their melting point ranges provided in Figure 6. A pure substance has a sharp melting point, while an impure substance has a broader melting point range.
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Sample A has a melting point range of 160-164°C.
- This range indicates that it is not a pure substance as it shows a variation in melting point.
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Sample B has a melting point of 166°C.
- This point is a single consistent temperature indicating it is likely pure.
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Sample C has a melting point range of 163-165°C.
- Similar to sample A, this indicates it is not pure due to variation in melting point.
Thus, only sample B is pure, while samples A and C are impure.
Step 3
Calculate the distance the spot of compound S moves if the solvent front has moved by 2.4cm.
Answer
To find the distance moved by the spot of compound S, use the formula related to the Rf value:
Given that Rf is 0.22 and the solvent front moved 2.4 cm, let d represent the distance the spot moves:
To find d, rearrange the formula:
Hence, the spot of compound S moves 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 difference in boiling points between sodium chloride (1465°C) and water (100°C) can be attributed to their differing structures and bonding types. Sodium chloride is an ionic compound, consisting of positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-) that are held together by strong ionic bonds. This results in a very high boiling point due to the energy required to break these bonds.
In contrast, water is a molecular substance with hydrogen bonds between water molecules. Although hydrogen bonds are strong, they are significantly weaker than ionic bonds, resulting in a lower boiling point for water.
This difference in boiling points is crucial for separating a sodium chloride solution into pure sodium chloride and pure water. By heating the solution, water will evaporate at its boiling point of 100°C while leaving behind solid sodium chloride. Upon complete evaporation of the water, pure dry sodium chloride can be collected.