Question

You dissolve 57.00 g sample of sodium phosphate solid in 599.o grams of water. All of the solid dissolves and the ionic compound breaks into individual ions when it dissolves to form an aqueous solution.

a) calculate the total number of sodium ions present in the solution

b) Calculate the ratio comparing the number of water molecules in the solution to the total number of ions ( cations and Anions) in the solution

c) If the total volume of the solution once mixed is 522.0ml, determine the density of the aqueous solution

d) you plan to heat the solution and boil the water at 100.) C until the ration of water molecules to ions is 10:1. Determine the present mass of the solution( mass of dissolved solid over total mass of solution) at this point

Answer 1

a)

Total amount of sodium phosphate() added = 57.00 g

Molar mass of = 163.94 g/mol

Hence, number of moles of can be calculated as

Note that each mole of dissociates to give 3 Na⁺ ion and one phosphate ion.

Hence, number of moles of Na⁺ ion in the solution can be calculated as

Each mole of any substance contains Avogadro's number of molecules. Hence, the number of Na+ ion in 1.043 mol of Na+ ion is

Hence, the number of Na⁺ ion in the solution is .

Note: answer rounded to 4 significant figures.

b)

Amount of water in the solution = 599.0 g

Molar mass of water = 18.01 g/mol

Hence, number of moles of water present is

Hence, the number of water molecules in the solution is

Now, we have already calculated the number of cations.

Note that for each phosphate ion there are 3 Na+ ion.

Hence, the number of phosphate anions can be calculated as

Hence, the ratio of water molecules to the sum of cations and anions can be calculated as

c)

Total volume of the solution after mixing, V = 522.0 mL

Total mass of the solution, m = 57.00 g + 599.0 g = 656.0 g

Hence, the density of the solution can be calculated as

d)

The ratio of water to ions is decreased by getting rid of some of the water by evaporation.

The new ratio of water to ions is 10.1.

We know that the number of ions is ,

Hence, the number of water molecules with the new ratio is

hence, the number of moles of water remaining in the solution can be calculated by dividing the number of molecules of water by Avodagro's number

Hence, the mass of water remaining is

Hence, total mass of the solution remaining is 250.5 g of water + 57.00 g of sodium phosphate = 307.5 g

Hence, the mass percent of the solution is