Question

The ocean on Planet “X” has only three major ions: Ca²⁺, SO₄^2- and Cl^-. Calculate the average salinity of the ocean on Planet “X” if the average concentrations of these major ions are: [Ca²⁺] = 14.00 mmol/L; [SO₄^2-] = 6.50 mmol/L; [Cl^-] = 15.00 mmol/L. Assume the density of the ocean on Planet “X” is similar to that on Earth.

Answer 1

Assuming the density of the ocean on Planet X is similar to that on the earth,

Since most of anions in seawater are chloride ions, the salinity is calculated from chloride ion concentration.

Salinity is usually expressed in parts per thousand (ppt), 1 ppt = 1000 mg/L

Salinity (ppt) = 0.0018066 X Cl ^- (mg/L) ----(1)

Given Chloride ion concentration is 15.00 mmol/L

To convert 15.00 mmol/L to mg/L, multiply with Chloride atomic weight 35.5 mg/mmol

15.00 mmol/L X 35.5 mg/mmol = 532.50 mg/L

Plug this value in Salinity equation number (1)

Salinity (ppt) = 0.0018066 X 532.50 mg/L = 0.9620 ppt = 962.0 mg/L