Question

a) Sea water contains roughly 28.0 g of NaCl per liter. (NaCl molar mass = 58.44 gmol-1).

i. Calculate the number of moles of NaCl in a liter of sea water.

ii. Calculate the molarity of NaCl in sea water.

iii. Calculate the mass by volume percent (W/V) of NaCl in sea water.

b) To identify the cations and anions present in an unknown solution, the following tests were carried out.

I. A flame test on the solid substance produces a brick red colour.

II. Nitric acid was added to a solution of the substance followed by a few drops

of barium nitrate solution. A white precipitate was formed.

i. What is the cation present in the substance?

ii. What is the anion present in the substance?

iii. Give the formula of the substance present.

Answer 1

Mass in a sea water = 28.0g per liter

Molar = 58.44

= 28.0/58.44 = 0.479moles

Molarity = moles/L

= 0.479/1

0.479 mol/L

Mass by volume percentage = 28/1000 × 100 = 2.8%