10mm acetate buffer(ph 4) is diluted one million times with distilled water (ph 7). Ph of this diluted buffer is
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10 ml acetate buffer (pH 4.0) is diluted one million times with distilled water (pH 7.0). pH of this diluted buffer is determined as follows.
Have a look at this first.
First, when you are mixing a buffer at pH 4.00 with water at pH = 7.00. The pH can never exceed 7.00 and this you will further see.
Again the pH of a buffer is normally determined by the ratio weak acid : conjugate base.
Diluting a buffer has minimal or no effect on the pH of the buffer. But in this problem you are carrying out excessive dilution. The concentration of weak acid and conjugate base becomes so low that the [H+] from the autoionisation of the water predominates. This implies that pH will be almost 7.00 or slightly below.
Then the calculations are as follows.
[H+] from the diluted buffer is 10^-10M
[H+] from the autoionisation of water = 10^-7M
Total [H+] = 10^-7M + 10^-10M = 1.001*10^-7 M
pH = -log 1.001*10^-7
pH = 6.9995