Question

Determine the grams of sodium carbonate required to precipitate Mg ²⁺   from water used in the wash cycle of a washing machine. Assume the volume of water for a full load in the wash cycle is 30 Liters, and the concentration of magnesium ions is 165 mg/L. Write a balanced chemical equation and determine the grams needed.

Answer 1

we know that

amount og Mg+2 ions = volume of water x conc of Mg+2

given

volume of water = 30 L

conc of Mg+2 ions = 165 mg / L

so

amount of Mg+2 ions = 30 x 165

amoung of Mg+2 = 4950 mg

now

we know that

moles = mass / molar mass

so

moles of Mg+2 = 4950 x 10-3 / 24

moles of Mg+2 = 206.25 x 10-3

now

the chemical equation is

Mg+2 + Na2C03 ---> MgC03 + 2Na+

we can see that

moles of Na2C03 required = moles of Mg+2 present

so

moles of Na2C03 required = 206.25 x 10-3

now

mass = moles x molar mass

so

mass of Na2C03 required = 206.25 x x 10-3 x 106

mass of Na2C03 required = 21.8625 g

so

21.8625 grams of Na2C03 is required