2014 final #8

Ivanna_Tang_3B
Posts: 22
Joined: Wed Sep 21, 2016 2:58 pm

2014 final #8

A buffer solution of volume 300.0 mL is 0.200M CH3COOH and 0.300M NaCH3CO2. The pKa for acetic acid is 4.75.

In part A, the initial pH of the solution is found to be 4.93.

Part B asks: what mass of NaOH would have to be dissolved in this solution to bring the pH to 6.0?
the solution writes: 6.0 = 4.75 + log{(0.300L * 0.300M + x)/(0.300L * 0.200M - x)}

why are x moles being added to the base and x moles subtracted from the acid?

thank you!

Daniel Namgoong 3I
Posts: 10
Joined: Wed Sep 21, 2016 2:56 pm

Re: 2014 final #8

It is because the addition of NaOH puts in extra OH- concentration which leads to a higher pH.

Samuel_Vydro_1I
Posts: 21
Joined: Fri Jul 22, 2016 3:00 am

Re: 2014 final #8

A higher pH corresponds to a higher amount of base as shown

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