Question

The seven most abundant ions in seawater make up more than 99% by mass of the dissolved compounds. Here are their abundances in units of mg ion/kg seawater: chloride 18,980; sodium 10,560; sulfate 2650; magnesium 1270; calcium 400; potassium 380; hydrogen carbonate 140. (a) What is the mass 96 of each ion in seawater? (b) What percent of the total mass of ions is sodium ion? (c) How does the total mass % of alkaline earth metal ions compare with the total mass 96 of alkali metal ions? (d) Which make up the larger mass fraction of dissolved components, anions or cations?

Answer 1

Answer:

Here's what I get  

Explanation:

(a) Mass % of each ion

$\text{Mass \%} = \dfrac{\text{mass}}{\text{total mass}} \times 100 \, \%\\\\= \dfrac{\text{mass}}{34 380} \times 100 \, \%\\= 2.903 \times 10^{-3} \times\text{"mass"} \, \%$

I used this template to calculate the percentages in the table below.

           Ion               Abundance                                   Mass %                

Na⁺                     10 560                                   30.72

K⁺                           380                                     1.11                  

Alkali metals                    10 940                                     31.82

Mg²⁺                     1 270                                      3.69

Ca²⁺                        400                                    1.16                  

Alkaline earth metals        1 670                                       4.86                

Total metal ions                            12 610                                      36.68

Cl⁻                     18 980                                     55.20

SO₄²⁻                  2 650                                       7.71

HCO₃⁻                   140                                        0.41

Anions                                          21 770                                      63.32

TOTAL                                         34 380                                     100.00

(b) 30.72 % of the total mass is sodium ion.

(c) Alkaline earth metals vs alkali metals

$\dfrac{\text{alkaline earth}}{\text{alkali}} = \dfrac{4.86}{31.82} = \dfrac{1 }{6.55}$

The mass percent of alkali metal ions is 6.55 times that of alkaline earth metal ions.

(d) The mass of anions is greater than that of cations.