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secondary 4 | Chemistry
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Hi,
Could you kindly advise me what's the correct answer for this MCQ question? And appreciate if you can explain more. Thank you so much :)
Date Posted: 3 years ago
Views: 643
Candice, in this case, we have to pay very close attention to the graphs.
Since the pH starts out above 7, the solution must have started out as an alkaline solution. Upon closer inspection, we realise that the pH is not very close to 14. If the diagram were to be drawn to scale, the value would be like 11. This is reflective of a weaker base like ammonia (sodium hydroxide has pH around 13 or 14).
The fact that the pH eventually drops to below 7 is indicative of an acid being added. This time, the graph continues to go down without plateuing at a good value, even towards the end (which seems to go to pH 1 or even 0). This suggests that a strong acid such as hydrochloric acid is added.
Ethanoic acid would likely bring the pH to 3 or 4, but not lower.
Thus, our best bet is aqueous ammonia for R and hydrochloric acid for S.
Since the pH starts out above 7, the solution must have started out as an alkaline solution. Upon closer inspection, we realise that the pH is not very close to 14. If the diagram were to be drawn to scale, the value would be like 11. This is reflective of a weaker base like ammonia (sodium hydroxide has pH around 13 or 14).
The fact that the pH eventually drops to below 7 is indicative of an acid being added. This time, the graph continues to go down without plateuing at a good value, even towards the end (which seems to go to pH 1 or even 0). This suggests that a strong acid such as hydrochloric acid is added.
Ethanoic acid would likely bring the pH to 3 or 4, but not lower.
Thus, our best bet is aqueous ammonia for R and hydrochloric acid for S.
Noted with thanks, Mr Eric :)
See 1 Answer
Ammonia has a lower pH as compared to sodium hydroxide. So it should start with ammonia. Hydrochloric acid is very acidic and a stronger acid than ethanoic acid. Adding hydrochloric acid to ammonia will neutralise it, and adding more of HCl will eventually make the solution acidic.
Choice is B
Choice is B
Hi Mr Raidah, thank you very much for your advice :)
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