pH=-log[H+]
H+ ions produced only by HCl,so [H+]= no of moles of H+/total
volume of solution
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=n/V
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=Molarity * volume of HCl added to the solution/V
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=1.25 mol/L * (80 * 10^-3 L)/(80+779) * 10^-3 L
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=100*10^-3 mol/859 * 10^-3 L
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=0.1164 mol/L
pH=-log (0.1164)=0.934 answer
