Question

Chemistry 

1. What is the ph of 100ml of aqueous solution containig 0.215g of trifluroomethane sulphonic acid (CF3SO3H) is completely ionized monoprotic acid

2. The solubility product of AgCl and AgPO4 are 1.6 x 10-10  and 1.8 x 10-18 respectively. If Ag+  are added to a litre of a solution  containing 0.10 mole of Cl- and PO43- . calculate the concentration of Ag+  ions in mL required to initiate : 

1. Precipitation of AgCl 
2. Precipitation of Ag3PO4

Answer 1

Part 1

Molecular weight of

$CF_3SO_3H=150g$

0.215g in 100ml is equivalent to

$\frac{1000}{100}×0.215=2.15g\\Molarity=\frac{2.15}{150}=0.01433M\\pH=-log_{10}[H_3O^+]\\=-log_{10}0.01433\\=1.844$

Part 2(a)

$AgCl_{(s)}\xrightleftharpoons{}Ag^+_{(aq)}+Cl^-_{(aq)}\\K_{sp}=[Ag^+][Cl^-]\\1.6×10^{-10}=[Ag^+][0.1]$

$[Ag^+]=1.6×10^{-9}$

Silver Chloride will begin to precipitate when the concentration of $Ag^+$ ions exceed $1.6×10^{-9}\>M$

Part 2 (b)

$Ag_3PO_{4(s)}\xrightleftharpoons{}3Ag^+_{(aq)}+PO_4\>^{3-}\>_{(aq)}$

$K_{sp}=[Ag^+]^3[PO_4\>^{3-}]\\1.8×10^{-18}=[Ag^+]^3[0.1]$

$[Ag^+]=2.62×10^{-6}$ M

for precipitation to start.