A sample of seawater contains 1.3g of calcium ions in 3,100kg of solution. what is the calcium ion concentration of this solution in units of ppm?

Unit ppm stands for parts per million. in terms of mass, ppm is equivalent to mg/kg.

since 1 kg is 10⁻⁶ mg, 1 kg is equivalent to million mg.

therefore mg/kg is also ppm.

there are 1.3 g of Ca ions in 3100 kg

if 3100 kg contains - 1.3 g of Ca

then 1 kg contains - 1.3 g / 3100 kg

then Ca ions - 0.42 x 10⁻³ g/kg

Ca ion concentration - 0.42 mg/kg

therefore Ca ion concentration is 0.42 ppm