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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 identify the number of each type of atom in the compound. Counting the atoms, we find:
- Carbon (C): 6
- Hydrogen (H): 12
- Oxygen (O): 1
The empirical formula is determined by simplifying the ratio of these atoms. The simplest whole number ratio of C:H:O from 6:12:1 is 6:12:1, which simplifies to C6H12O. 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
Using the melting point data from Figure 6:
- Sample A has a melting point range of 160-164 °C.
- Sample B has a melting point of 166 °C.
- Sample C has a melting point range of 163-165 °C.
Since sample B has a melting point that is distinct and outside the range of samples A and C, it indicates that sample B is pure. In contrast, samples A and C have overlapping melting point ranges, suggesting they may contain impurities. A pure substance typically has a sharp melting point, while impure samples exhibit a broader melting range due to the presence of different components affecting the melting process. Hence, samples A and C are considered impure.
Step 3
Calculate the distance the spot of compound S moves if the solvent front has moved by 2.4 cm.
Answer
Given the Rf value of compound S is 0.22, we can calculate the distance the spot has moved using the formula:
Let the distance moved by substance be represented as 'x'. Plugging in our values, we have:
To find 'x', we rearrange the equation:
Thus, the distance the spot 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.
Answer
Sodium chloride (NaCl) is an ionic compound composed of sodium ions (Na+) and chloride ions (Cl-), which are held together by strong electrostatic forces known as ionic bonds. The solid structure of sodium chloride forms a lattice arrangement, requiring substantial energy to break these bonds, which is why it has a high boiling point of 1465 °C.
On the other hand, water (H2O) is a molecular compound where hydrogen bonds exist between water molecules. These bonds are much weaker compared to ionic bonds, resulting in a lower boiling point of 100 °C.
When separating a sodium chloride solution into dry sodium chloride and pure water, this significant difference in boiling points allows for a simple distillation process. Water can be boiled away while leaving the solid sodium chloride behind. Thus, the choice of method is based on the distinct structural characteristics and bonding types present in sodium chloride and water.