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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: mglbs on February 23, 2021, 07:35:06 AM

Title: pH value of NaCl+HCl
Post by: mglbs on February 23, 2021, 07:35:06 AM

How can I calculate the pH value if I add 30g NaCl in 20ml HCl with 0.2 mol/L?

I tried to calculate it and got a pH of 1.4 is it right? Can NaCl effect the pH?

Title: Re: pH value of NaCl+HCl
Post by: AWK on February 23, 2021, 09:02:13 AM

Nonsense - show your calculations.
About 5 g of NaCl will be dissolved in 20 ml of 0.2 M HCl. Sodium chloride lowers the pH of hydrochloric acid a little, but this is difficult to calculate.

Title: Re: pH value of NaCl+HCl
Post by: mglbs on February 23, 2021, 09:32:31 AM

I did it like that

Title: Re: pH value of NaCl+HCl
Post by: AWK on February 23, 2021, 09:52:21 AM

Unrecognizable format.

Title: Re: pH value of NaCl+HCl
Post by: mglbs on February 23, 2021, 10:35:21 AM

V(HCl)=0.02L c(HCl)=0.2mol/L

30g NaCl  M= 83 g/mol  n(NaCl) = 0.517 mol

n(HCl)=4⋅10⁻⁴ mol

c(H⁺)= (0.517 mol − 4⋅10^-4 mol) / 0.02L = 25.83mol/L

pH=-log(c(H⁺))=1.4

Title: Re: pH value of NaCl+HCl
Post by: AWK on February 23, 2021, 10:44:46 AM

M NaCl = 58.5
NaCl in solutions is nearly neutral.

Title: Re: pH value of NaCl+HCl
Post by: mglbs on February 23, 2021, 12:05:49 PM

So what I did is wrong

Title: Re: pH value of NaCl+HCl
Post by: AWK on February 23, 2021, 12:20:31 PM

1. This amount of  NaCl will not dissolve.
2. Formula weight of NaCl is different.
3. If you cannot account for the activity factors for high ionic strengths, just calculate the pH of a pure acid.