In order to determine the salinity of a water sample, a student measured 50.0 ml

Question

In order to determine the salinity of a water sample, a student measured 50.0 ml of a salt water solution (density=1.021 g/ml) into a flask. The Cl minus in the measured sample required 16.67 ml of 1.0466 M AgNO3 solution to reach the end point.

(a) What is the number of mols of Ag plus used?

(b) What is the number of mols of Cl minus in the salt water solution?

(c) What is the number of mols of NaCl in the solution?

(D) What is the number of grams of NaCl in the solution?

(e) What is the percent by mass of NaCl in the solution?

Explanation / Answer

a)
moles Ag+ used = 0.01667 L x 1.0466 mol/L= 0.01745

b)
The net ionic equation is
Ag+ (aq) + Cl- (aq) = AgCl (s)
the ratio between Ag+ and Cl- is 1 : 1
moles Cl- = 0.01745

c)
moles NaCl = 0.01745

d)
mass NaCl = 0.01745 mol x 58.44 g/mol=1.020 g

e)
mass solution = 50.0 mL x 1.021 g/mL=51.05 g
% by mass NaCl = 1.020 x 100 / 51.05 =1.998

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