## Ch 14 #107

$E_{cell} = E_{cell}^{\circ}-\frac{RT}{nF}\ln Q$

Michael Lonsway 3O
Posts: 43
Joined: Wed Sep 21, 2016 2:57 pm

### Ch 14 #107

What range (in volts) does a voltmeter need to have to measure PH in the range of 1 to 14 at 25 degrees Celsius if the voltage is zero when PH=7?

How can we relate PH to the equations we've used for electrochem and solve this problem?

Aileen Nguyen 3N
Posts: 26
Joined: Wed Sep 21, 2016 2:56 pm
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### Re: Ch 14 #107

To relate pH to the equations we learned,
E° has to be 0 when pH 7 since pH=7 when concentration of H+ and OH- are equal to 1.0 x 10^-7 mol.L^-1
when k=1 E°is 0

take ∆G°=-nFE°and ∆G°=RTlnK and then you get E°= RT/nF (lnK)

at pH=7: K= [H+]/[OH-]= 1.0 x 10^-7 mol.L^-1/1.0 x 10^-7 mol.L^-1= 1 and E = 0

at pH=1: RT/nF ( lnK)= .025693 V (ln 1.0 mol.L^-1/ 1.0 x 10^-14 mol.L^-1)= +.828 V

at pH=14: RT/nF ( lnK)= .025693 V (1.0 x 10^-14 mol.L^-1/ln 1.0 mol.L^-1)= -.828 V

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