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Chemistry

Screenshot of question n the following post.
Reply 1
Avatar for abdullahAK
abdullahAK
OP
14
Can anyone help me with the question below.
kk.PNG31.0KB
Reply 2
Avatar for Pigster
Pigster
20
Original post by abdullahAK
Can anyone help me with the question below.

What are your thoughts about A - D? What would be in each solution?
Reply 3
Avatar for abdullahAK
abdullahAK
OP
14
I think C because salts are neutral.
Reply 4
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abdullahAK
OP
14
But according to the mark scheme,
Answer is part D.
How?
Reply 5
Avatar for Pigster
Pigster
20
Original post by abdullahAK
I think C because salts are neutral.

The Q expects salt and acid. How much acid is present (slightly above) neutral?
Its D because after neutralization we add excess acid because ph reduces after naturalization
Reply 7
Avatar for abdullahAK
abdullahAK
OP
14
I didn't get it,could you rephrase it.


Original post by Pigster
The Q expects salt and acid. How much acid is present (slightly above) neutral?
Reply 8
Avatar for Nour M.
Nour M.
14
Original post by abdullahAK
But according to the mark scheme,
Answer is part D.
How?

Okay, so what you need to do is understand what is happening in the graph. What's essentially happening is you're adding acid to an alkali to form water and salt (both are neutral btw). The question doesn't tell you when to stop so you can assume you'll keep adding acid til all the alkali reacts + some excess acid. Now at point A, the pH hadn't changed from 14 (Alkali), so that means there is probably still no acid added to the alkali, meaning A can't be the answer as there is no acid nor salt as no neutralisation had taken place. Point B is probably the point at which acid had been added to the alkali as there is an evident drop in pH, meaning neutralisation is taking place. At this point, we've got alkali, acid and probably a little bit of salt and water present. The question clearly asks at which point is both acid and salt present. This implies that there's probably no alkali left as it's not mentioned. Points B and C are both above the neutral pH, meaning there's still a bit of alkali left as water and salts are neutral. So we're left with point D. It's clear at this point, that all the alkali had been used up, and that we've got an excess of acid as the pH is well below neutral (pH 7). This tells us that we've got only salts present from the previous neutralisation reaction (probably dissolved in the water) as well as some excess acid which caused the pH to be lower than pH 7 (no alkali present). So that's why D is right.
(edited 4 years ago)
Reply 9
Avatar for abdullahAK
abdullahAK
OP
14
Thank you for giving such a comprehensive answer.
:smile:
Anytime :tongue:
Original post by abdullahAK
Thank you for giving such a comprehensive answer.
:smile:

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