1. What is a Standard Solution?
A standard solution is a solution for which the concentration is accurately known.
We can use these solutions to determine the concentrations of other unknown solutions.
In a primary standard, the concentration is determined by directly weighing a reactant and then dissolving it in a known volume of water. (C=n/V)
For a substance to be suitable as a primary standard…
It must be available in its pure form.
It must resist absorbing water.
It must be stable when stored (un-reactive).
It must have a high molar mass so weighing errors are less significant.

2. Making a Standard Solution
Step 1: Decide the concentration and the volume of solution that you require.
Step 2: Use the equation c=n/V to find out how many moles of solute you need based on your concentration and volume requirements from step 1.
Step 3: Convert moles to grams using the equation m=nM. This is how much solute you need to weigh out.
Step 4: Transfer your solute to an appropriate volumetric flask and fill up to the line with distilled water. Make sure ALL the solute is dissolved before use.
Step 5: Label the flask with the name of the primary standard and its concentration.

3. Prepare 250 mL primary standard containing 2.7g Na2CO3.
Step 1: Complete.
Step 2: Concentration = 0.50 mol L-1 , Volume = L
n = (0.50 mol L-1)(0.500L) = 0.25 mol
Step 3: n = 0.25 mol, M = 254 g mol-1
m = (0.25 mol)(254 g mol-1) = 63.5 g
Step 4: Get a 500 mL volumetric flask, put your 63.5 g of K2Cr2O7 into it and fill to the line with distilled water. Make sure all the solid dissolves.
Step 5: Label the flask.