Question

Seawater contains approximately 3.5 %NaCl by mass and has a density of 1.02 g/mL. What volume of seawater contains 5.0 g of sodium? Please clearly show steps!

Answer 1

Molar mass of Na = 22.99 g/mol

mass(Na)= 5.0 g

number of mol of Na,

n = mass of Na/molar mass of Na

=(5.0 g)/(22.99 g/mol)

= 0.2175 mol

This is number of moles of Na

one mole of NaCl contains 1 moles of Na

So, number of moles of NaCl = number of moles of NaCl / 1

= 0.2175 / 1

= 0.2175

Molar mass of NaCl,

MM = 1*MM(Na) + 1*MM(Cl)

= 1*22.99 + 1*35.45

= 58.44 g/mol

mass of NaCl,

m = number of mol * molar mass

= 0.2175 mol * 58.44 g/mol

= 12.71 g

Now calculate mass of sea water

mass % = mass of NaCl * 100 / mass of sea water

3.5 = 12.71*100 / mass of sea water

mass of sea water = 363.1 g

now use:

density = mass of sea water / volume

1.02 g/mL = 363.1 g / volume

volume = 356 mL

Answer: 356 mL