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.

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.

Prepare 250 mL primary standard containing 2.7g Na2CO3. Step 1: Complete. Step 2: Concentration = 0.50 mol L-1 , Volume = 0.500 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.