# chemistry question a-level

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#1
A student dilutes 25.0 cm3 of 0.500 mol dm–3 propanoic acid by adding water until the total volume is 100.0 cm3
Calculate the pH of this diluted solution of propanoic acid. Give your answer to 2 decimal places.

0
6 months ago
#2
How did you go about working this out.
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#3
(Original post by great0)
How did you go about working this out.
why? am i wrong
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6 months ago
#4
(Original post by cherrybunny)
why? am i wrong
you might be right
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6 months ago
#5
I am also interested in how you arrived at your answer. I'm more used to working out pH of solutions when strong acids/bases are involved. I'm curious as to how you got past the idea that propanoic acid only partially dissociates - did you have some sort of dissociation constant?
Last edited by Pyruvic Acid; 6 months ago
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6 months ago
#6
(Original post by cherrybunny)
A student dilutes 25.0 cm3 of 0.500 mol dm–3 propanoic acid by adding water until the total volume is 100.0 cm3
Calculate the pH of this diluted solution of propanoic acid. Give your answer to 2 decimal places.

Since Ka = 1.35 x 10^-5, you should have got 2.89.

I guess you've divided the conc. by three (since you're adding three volumes of water to the 25 to make 100. But if you think about it, you divide the conc. by four, since the volume is 4x larger than when you started.
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#7
(Original post by Pigster)
Since Ka = 1.35 x 10^-5, you should have got 2.89.

I guess you've divided the conc. by three (since you're adding three volumes of water to the 25 to make 100. But if you think about it, you divide the conc. by four, since the volume is 4x larger than when you started.
ahh i see, i was actually working out the no. of moles and then i did the moles / (75/1000) which gave me 0.1666 as the conc lol, i know it was wrong but i didnt know how to go about this question
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