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chemistry help for a level ocr

why do you work out the moles instead of using the initial concentrations. I can't remember why
(c). The chemist prepares 1dm3 of a buffer solution by mixing 200 cm3 of 0.200 mol dm−3 HNO2 with 800 cm3 of 0.0625 mol dm−3
sodium nitrite, NaNO2.
i. Calculate the pH of the buffer solution.
Give your answer to two decimal places.

ka = 4.69 × 10−4
and the answer is 3.43
(edited 1 year ago)
Original post by grace10101
(c). The chemist prepares 1dm3 of a buffer solution by mixing 200 cm3 of 0.200 mol dm−3 HNO2 with 800 cm3 of 0.0625 mol dm−3
sodium nitrite, NaNO2.
i. Calculate the pH of the buffer solution.
Give your answer to two decimal places.
ka = 4.69 × 10−4
and the answer is 3.43

But how?
Reply 3
Original post by grace10101
why do you work out the moles instead of using the initial concentrations. I can't remember why


Because the total volume changes when you add together the solutions. Hence volume of the buffer components also changes… you can work out the rest

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