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This question is about hydrogen chloride and hydrochloric acid - AQA - GCSE Chemistry Combined Science - Question 6 - 2022 - Paper 1
Question 6
This question is about hydrogen chloride and hydrochloric acid. 1. Complete the dot and cross diagram to represent the bonding in hydrogen chloride on Figure 7. Us... show full transcript
Worked Solution & Example Answer:This question is about hydrogen chloride and hydrochloric acid - AQA - GCSE Chemistry Combined Science - Question 6 - 2022 - Paper 1
Step 1
Complete the dot and cross diagram to represent the bonding in hydrogen chloride on Figure 7.
Answer
In the dot and cross diagram for hydrogen chloride (HCl), the hydrogen atom contributes one electron (shown as a dot) and the chlorine atom contributes one electron (shown as a cross) to form a single bond. Therefore, the diagram should depict one shared pair of electrons between hydrogen and chlorine, with six non-bonding electrons remaining on the outer shell of chlorine.
Step 2
Step 3
Describe how magnesium can be used to distinguish between a strong acid and a weak acid of the same concentration.
Answer
Magnesium reacts with strong acids at a greater rate than with weak acids. When magnesium is added to a solution, it will react vigorously with a strong acid, producing hydrogen gas rapidly, while in the presence of a weak acid, the reaction will be significantly slower or may not occur at all.
Step 4
What is the change in pH?
Answer
When the concentration of hydrochloric acid is increased by a factor of 100, the pH decreases by 2 units. This is because pH is a logarithmic scale and an increase in hydrogen ion concentration by a factor of 100 corresponds to a decrease of 2 in pH (from the formula pH = -log[H+]).
Step 5
Calculate the bond energy X.
Answer
The bond energies for the reaction can be calculated as follows:
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Bonds broken: (4 × 413) + (C=C + 431) = 2083 + X
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Bonds made: (346 + 339) + (5 × 413) = 2750
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The energy released is given as 56 kJ/mol greater than the energy needed to break the bonds. Therefore, we set up the equation:
ext{Energy released} = ext{Bonds broken} - ext{Bonds made}
This gives: 56 = (2750) - (2083 + X)
Solving for X gives: X = 611 kJ/mol.
Thus, the value of bond energy X is 611 kJ/mol.