138 9 · CALCULATING CONCENTRATIONS
Standard solutions
Astandard solutionis a solution of known concentration. Primary standardsare
substances that are used to make up standard solutions, by accurately weighing out a
given mass of the standard, then dissolving the standard in deionized (i.e. pure)
water to make up a known volume of solution. Primary standards should be:- chemically stable in the solid and aqueous states
- pure
- soluble in water.
Anhydrous sodium carbonate is an example of a primary standard. Standard
solutions of primary standards can be used to standardize other solutions, as you
will see in the next section.9.2
Assuming the following compounds are completely ionized in solution, identify the ions that
exist in the following aqueous solutions and state the concentration of each ion.
(i) Potassium chloride, KCl (0.1 mol dm^3 )
(ii)Sodium carbonate, Na 2 CO 3 (0.125 mol dm^3.
(iii)Ammonium sulfate, (NH 4 ) 2 SO 4 (0.25 mol dm^3 ).
(iv)Copper nitrate, Cu(NO 3 ) 2 (0.15 mol dm^3 ).Exercise 9B
Calculating the concentration of standard solutions
An aqueous solution containing 0.10 mol of anhydrous sodium carbonate (Na 2 CO 3 ) is placed
in each of the volumetric flasks, and carefully diluted with deionized water to each of the
volumes shown. Calculate the concentration of each solution.(i)V2000 cm^3 (ii)V1000 cm^3 (iii)V500 cm^3 (iv)V250 cm^3 (v)V100 cm^3Exercise 9C