Calculate the ratio of NaF to HF required to create a buffer with pH = 4.00ZS

Redemitz4s

Redemitz4s

Answered question

2021-11-21

Calculate the ratio of NaF to HF required to create a buffer with pH=4.00

Answer & Explanation

John Twitchell

John Twitchell

Beginner2021-11-22Added 19 answers

We want to derive the expression to HF 
pH=pKa+log[F][HF] 
pH=pKa+log[NaF][HF]  
So, [NaF][HF]=10pHpKa =10pH(logKa) =10pH+logKa =104.00+log(3.5×104) 
Answer is 3.5

Kara Dillon

Kara Dillon

Beginner2021-11-23Added 12 answers

Step 1
Answer is explained below.
The given buffer contains NaF (salt of weak acid & strong base) & HF(weak acid) that means it is a acidic buffer.
pH of the buffer is 4.00 (given) & Ka of HF is 6.6×104.
Step 2
Now, from Henderson Equation we get,
pH=pKa+log(NaFHF)4.00=log(6.6×104)+log(NaFHF)log(NaFHF)=0.82
(NaFHF)=6.6
Thus, the ratio of NaF to HF required to create a buffer with pH=4.00, is 6.6:1.

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