Help please. Am doing a past exam paper and I hit a road block with this question:
Chloride in a brine solution is determined by a precipitation titration. A 10.00 mL
aliquot of the solution is titrated with 15.00mL of standard 0.1182 M AgNO3
solution. The excess silver is titrated with standard 0.1010 M KSCN solution,
requiring 2.38 mL to reach the red Fe(SCN)2+ endpoint. Calculate the
concentration of chloride in the brine solution, in g/1000mL.
Do I calculate the moles of KSCN and the moles of AgNO3
.
Moles reacted: moles AgNO3 - moles KSCN
Then say : C =mols reacted/volume(the 10 ml volume x 10 to the minus 3)
Then multiply mol/L by g/mol , then convert to g/ml
Please help.Thank you!
Yes, you are on the right track! To calculate the concentration of chloride in the brine solution, you need to follow these steps:
1. Calculate the moles of AgNO3 used in the precipitation titration:
moles of AgNO3 = concentration of AgNO3 (in M) × volume of AgNO3 (in L)
In this case:
concentration of AgNO3 = 0.1182 M
volume of AgNO3 = 15.00 mL = 15.00 × 10^(-3) L
So, moles of AgNO3 = 0.1182 M × 0.01500 L
2. Calculate the moles of KSCN used in the excess titration:
moles of KSCN = concentration of KSCN (in M) × volume of KSCN (in L)
In this case:
concentration of KSCN = 0.1010 M
volume of KSCN = 2.38 mL = 2.38 × 10^(-3) L
So, moles of KSCN = 0.1010 M × 0.00238 L
3. Calculate the moles of reacted species:
moles reacted = moles of AgNO3 - moles of KSCN
4. Determine the concentration of chloride in the brine solution:
concentration of chloride (in mol/L) = moles reacted / volume of brine solution (in L)
In this case, the volume of the brine solution aliquot is given as 10.00 mL = 10.00 × 10^(-3) L
So, concentration of chloride = moles reacted / 0.01000 L
5. Convert the concentration from mol/L to g/1000mL:
concentration of chloride (in g/1000mL) = concentration of chloride (in mol/L) × molar mass of chloride (in g/mol)
You can find the molar mass of chloride by looking up the atomic masses of Cl from the periodic table.
6. Finally, multiply the concentration (in g/1000mL) by 100 to get the concentration in g/L.
By following these steps, you should be able to calculate the concentration of chloride in the brine solution. Good luck with your exam!