Question

a student takes a sample of water with a salinity of 21 ‰ or psu and allows the water to evaporate, leaving behind 21 grams of residual salts. the student then measured 11.56 grams of chloride ions in the salts. following the rule of constant proportions, how many grams of sodium ions were in the sample of water?

Explanation:

Step1: Find the mass of sodium ions

We know that the total mass of residual salts is \(m = 21\) grams and the mass of chloride ions is \(m_{Cl}=11.56\) grams. Let the mass of sodium ions be \(m_{Na}\).
Since \(m = m_{Na}+m_{Cl}\) (by the law of conservation of mass for the salts in the sample).

Step2: Calculate \(m_{Na}\)

Substitute the values into the formula: \(m_{Na}=m - m_{Cl}\)
\(m_{Na}=21 - 11.56\)
\(m_{Na}=9.44\)

Answer:

\(9.44\)