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A buffer is prepared by adding 300.0 ml of 2.0 mnaoh to 500.0 ml of 2.0 mch3cooh. what is the ph of this buffer? ka= 1.8 10-5(ans. 4.92)

Respuesta :

The pH of the buffer is 4.523 .

Given,

A buffer is prepared by adding 300 ml of 2M NaOH to 500 ml of 2M CH3COOH .

Thus , the volume of NaOH =300ml

volume of CH3COOH = 500ml

molarity of NaOH = 2M

Molarity of CH3COOH =2M

because of adding the two compound ,

the total volume =( 300+500)ml =800ml

We know ,

number of moles = molarity ×volume

number of moles of NaOH = 300ml×2M = 600mol

number of moles of CH3COOH = 500ml×2M = 1000ml

Due to mixing of NaOH and CH3COOH , there is a change in volume and concentration .

We know ,

molarity = number of moles /total volume

concentration of NaOH = 600mol/800ml = 0.75M

concentration of CH3COOH = 1000mol/800ml =1.25M

We know ,

pH = pKa + log {[base ]/[acid]}

pH = -log(1.8×10^-5) + log{[0.75]/[1.25]}

pH = 4.744 + (-0.221)

pH = 4.523

Hence , the pH of the buffer is 4.523 .

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