SME
Oceanography · Problem type
Salinity from chlorinity
Use this for “Seawater has a chlorinity of 19.37 g/kg. What is its salinity, and how much sodium is in each kilogram?”
Chart
19.2 + 10.7 + 2.69 + 1.29 + 0.420 + 0.385 + 0.245 = 34.99 g/kg.
This is an example. Type your own values to start a new problem.
S (g/kg)
=
1.80655
×
Cl (g/kg)
m (g/kg)
=
S (g/kg)
×
p
÷
100
Formulas
S
=
1.80655
×
Cl
34.9929 = 1.80655 × 19.37
m
=
S
×
p
100
10.7078
=
34.9929
×
30.6
100
Assumptions
•
The major ions keep fixed proportions in all seawater (Forchhammer’s principle), so measuring chloride gives the salinity: S = 1.80655 Cl.
•
Shares by mass: chloride 55 %, sodium 30.6 %, sulfate 7.7 %, magnesium 3.7 %, calcium 1.2 %, potassium 1.1 %, others 0.7 %.
•
Rain, rivers and evaporation change how much salt there is, not its recipe.
Step-by-step
WE KNOW
Cl = 19.37 g/kg, p = 30.6%
FIND
salinity (S), the ion’s mass (m)
Step 1 · Find salinity (S)
Use S = 1.80655 × Cl
Chloride is a fixed share of the salt, so the salinity is 1.80655 times the chlorinity.
S
=
1.80655
×
19.37
S
=
34.9929
g/kg
Step 2 · Find the ion’s mass (m)
Use m = S × p ÷ 100
The ion’s share of every kilogram’s salt.
m
=
34.9929
×
30.6
100
m
=
1,070.8
100
m
=
10.7078
g/kg
Check
Put the numbers back in. Both sides should match.
34.9929 = 1.80655 × 19.37 ✓
10.7078
=
34.9929
×
30.6
100
✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.