[student8607]

There’s actually much more in seawater than just dissolved NaCl. Major ions present include 19,000ppm Cl^-, 10,500ppm Na⁺, 2650ppm SO₄^2-, 1350ppm Mg²⁺, 400ppm Ca²⁺, 380ppm K⁺, 140ppm HCO₃^-, and 65ppm Br^-.
What is the total molarity of all ions present in seawater?

Any advice on where to start?

I know ppm is a form of mass% (10⁶)

[macman104]

Well, you have the ppm, and you can find the molecular weight of all these ions, so can you find the moles of each ion present?

[student8607]

Well, you have the ppm, and you can find the molecular weight of all these ions, so can you find the moles of each ion present?

If I divide each ppm by 10⁶ then I just get back to the mass%.
How can I find the individual masses?

[macman104]

Define ppm.  Don't just say it is a type of mass%, for example:

Molarity is not just a type of concentration, it is:

moles of solute per liter of solution.

So define ppm,

It is...

[student8607]

Define ppm

(mass of component / total mass of solution) x 10⁶

[Borek]

(mass of component / total mass of solution) x 10⁶

So what do you need?

Assume 1 liter of solution. Either google sea water density, or assume it is that of pure water, 1 g/mL.

[AWK]

An useful defintion of ppm is 1_mg_of_solute/1_kg _of_solution (for diluted water solution you can use liters instead of kilograms).
Hence convert ppm into miligram, then grams.
Next step is the mole calculations for ich ion.
Sum of moles will give you a total molarity since calculations were done for 1kg (~1Liter).

[student8607]

Assume 1 liter of solution. Either google sea water density, or assume it is that of pure water, 1 g/mL.

1g/mL x 1000mL = 1000g
so 1,000g for total mass

now that I have total mass (denominator), I can just divide the ppm by 10⁶ and then multiply by the total mass to solve for individual masses?

[student8607]

19,000ppm x 10-6 = 0.019g
10,500ppm x 10-6 = 0.0105g
2650ppm    x 10-6 = 0.00265g
1350ppm    x 10-6 = 0.00135g
400ppm      x 10-6 = 0.0004g
380ppm      x 10-6 = 0.000380g
140ppm      x 10-6 = 0.000140g
65ppm        x 10-6 = 0.000065g

D=M/V
1.0g/mL = (?g) (1000mL)
1000g = total mass

Mass percent: mass of component / total mass
x / 1000 = 0.019g --> 19g of Cl-
x / 1000 = 0.0105g --> 10.5g of Na+
x / 1000 = 0.00265g --> 2.65g of SO42-
x / 1000 = 0.00135g --> 1.35g of Mg2+
x / 1000 = 0.0004g --> 0.40g of Ca2+
x / 1000 = 0.000380g --> 0.380g of K+
x / 1000 = 0.000140g --> 0.140g of HCO3-
x / 1000 = 0.000065g --> 0.065g of Br-

Molecular masses (amu): Cl=35.5, Na=23.0, SO4=96.1, Mg=24.3, Ca=40.1, K=39.1, 61.0g=HCO3, Br=79.1
 
19g x 1mol / 35.5g = 0.54mol Cl-
10.5g x 1mol / 23.0g = 0.457mol Na+
2.65g x 1mol / 96.1g = 0.0276mol SO42-
1.35g x 1mol / 24.3g = 0.0556mol Mg2+
0.40g x 1mol / 40.1g = 0.0010mol Ca2+
0.380g x 1mol / 39.1g = 0.00972mol K+
0.140g x 1mol / 61.0g = 0.00230mol HCO3-
0.065g x 1mol / 79.1g = 0.00082mol Br-
Total moles: 1.09moles

M = 1.09moles / 1L = 1.09M

[AWK]

Density of ocean water with 35,000 ppm of salts is about 1.027 kg/L
Hence your calculations are underestimated by ~3 %

[student8607]

Density of ocean water with 35,000 ppm of salts is about 1.027 kg/L
Hence your calculations are underestimated by ~3 %

Thanks. How about this then:

19,000ppm x 10-6 = 0.019g
10,500ppm x 10-6 = 0.0105g
2650ppm    x 10-6 = 0.00265g
1350ppm    x 10-6 = 0.00135g
400ppm      x 10-6 = 0.00040g
380ppm      x 10-6 = 0.000380g
140ppm      x 10-6 = 0.000140g
65ppm        x 10-6 = 0.000065g

D=M/V
1027g/L = (?g) (1L)
1027g = total mass

Mass percent: mass of component / total mass
x / 1027 = 0.019g  19.5g of Cl-
x / 1027 = 0.0105g  10.8g of Na+
x / 1027 = 0.00265g  2.72g of SO42-
x / 1027 = 0.00135g  1.39g of Mg2+
x / 1027 = 0.00040g  0.41g of Ca2+
x / 1027 = 0.000380g  0.390g of K+
x / 1027 = 0.000140g  0.144g of HCO3-
x / 1027 = 0.000065g  0.067g of Br-

Molecular masses (amu): Cl=35.5, Na=23.0, SO4=96.1, Mg=24.3, Ca=40.1, K=39.1, 61.0g=HCO3, Br=79.9
 
19.5g x 1mol / 35.5g = 0.55mol Cl-
10.8g x 1mol / 23.0g = 0.470mol Na+
2.72g x 1mol / 96.1g = 0.0283mol SO42-
1.39g x 1mol / 24.3g = 0.0572mol Mg2+
0.41g x 1mol / 40.1g = 0.010mol Ca2+
0.390g x 1mol / 39.1g = 0.00997mol K+
0.144g x 1mol / 61.0g = 0.00236mol HCO3-
0.067g x 1mol / 79.9g = 0.00084mol Br-
Total moles: 1.13moles

M = 1.09moles / 1L = 1.13M

[ARGOS++]

Dear student8607;

Not exactly!, - and very complicated.

Much easier from definition of ppm: 
          1.09 moles / 1.000 kg = 1.09 moles / (1kg / 1.027 kg/L) = 1.12 M.

Good Luck!
                    ARGOS⁺⁺