Question

Table 1. Seawater major constituent concentrations. (Concentrations for salinity = 34.7‰.)

Table 1 information: Constituent: Chlorine , % of total salinity: 55.04, parts per million: 18980

1. Table 1 indicates that the concentration of Cl-  in a sample of sea water with a salinity of 34.7 is 18,980 ppm. This means that there are 18,980g of Cl- every ____ of water.

a. 1,000 g
b. 10,000 g
c. 100,000 g
d. 1,000,000 g
e. 1,000,000 kg

2. Therefore, the concentration of Cl- in the same sample can also be expressed as ____ (remember that 1,000g = 1 kg)

a. 18,980 g/1,000 g = 18,980 g/kg
b. 18,980 g/10,000 g = 1,898 g/kg
c. 18,980 g/100,000 g = 189.8 g/kg
d. 18,980 g/1,000,000 g = 18.98 g/kg
e. 18,980 g/1,000,000 kg = 0.019 g/kg

3. Using the Principle of Constant Proportions we know that the ratio of the major constituents always remains the same in seawater, which also means that the ratio ion concentration/seawater salinity is constant. Therefore we can write _____, where x is the unknown concentration of Cl-.

a. (34.7/0.019)=(32.8/x)
b. (18.98/34.7)=(x/32.8)
c. (189.8/34.7)=(x/32.8)
d. (34.7/1,898)=(32.8/x)
e. (18,980/34.7)=(x/32.8)

4. Hence, the concentration of Cl- in seawater with a salinity of 32.8 is __ g/kg.

a. 0.018
b. 17.94
c. 179.4
d. 1,794
e. 17940.7

Answer 1

1) Assume the density of sea water is 1 g/mL.

The Cl^- concentration is 18980 ppm. We know that 1 ppm = 1 mg/L; therefore, 18980 ppm = 18980 mg/L.

Again, the mass of 1 L of water = (1 L)*(1000 mL/1 L)*(1 g/1 mL) = 1000 g.

Therefore, we can write 18980 ppm = 18980 mg/L = 18980 mg/1000 g; thus, we have (a) 1000 g of water.

2) We know that 1000 g = 1 kg; therefore, we can write the Cl^- concentration as 18980 mg/1000 g = 18980 mg/kg. Therefore, (a) is the correct answer.

3) The concentration for salinity is 18980 ppm while the salinity is 34.7%; therefore, we have 18980/34.7 = x/32.8 where 32.8% is the salinity and x is the unknown Cl^- concentration. (e) is the correct answer.

4) Solve the above equation and obtain

x = 18980*32.8/34.7 = 17940 g/kg (ans).