How to Make a Standard Solution – HSC Chemistry


This is part of Year 11 HSC Chemistry course under the topic of Molarity.

HSC Chemistry Syllabus

  • conduct an investigation to make a standard solution and perform a dilution

  • Manipulate variables and solve problems to calculate concentration, mass or volume using: 
– `c = \frac{n}{V}` (molarity formula (ACSCH063))

      Step by Step Explanation on Making a Standard Solution

      What is a Standard Solution?

      A standard solution is a solution whose concentration is known accurately. It's commonly prepared by dissolving a primary standard, a specific solute, in an appropriate solvent such as distilled/de-ionised water.

      Primary Standard

      A primary standard is a solute used to prepare a standard solution. It must fulfil the following criteria:

      • High level of purity and accurately known composition: when calculating the required mass of a primary standard, it is assumed that no impurities contribute to the measured mass. For example, if 2.00 g of sodium carbonate is to be measured, it is assumed that the 2.00 g sample contains only sodium carbonate, and no other impurities. 
      • Stable and unaffected by air when weighing: some substances are hygroscopic meaning they readily absorb moisture in air, which affects the composition and purity of the substance. 
      • Readily soluble in solvent of choice: the measured quantity of primary standard should entirely dissolve in the solvent without forming a precipitate.
      • High molar/molecular weight: any changes in measured mass of the primary standard correspond to a small difference in number of moles. 
      • Quickly and completely reacting: this is more relevant when the primary standard solution is to be used to determine the concentration of another solution, such as in titration.

      Examples of substances unsuitable for making primary standard solutions

      • Hydrochloric acid (HCl) of very high concentration because it becomes volatile, resulting in losses as fumes
      • Sodium hydroxide (NaOH) because it is hygroscopic (absorbs water)


      Examples of good primary standard solutions

      • Oxalic acid
      • Benzoic acid
      • Anhydrous sodium carbonate
      • Anhydrous sodium hydrogen carbonate

      Note that anhydrous compounds are prepared by drying in an oven until all water content is evaporated (mass remains constant).

      Secondary Standards

      Secondary standards are solutions whose concentrations are not known precisely from preparation but are determined by calibration against a primary standard solution. They are used where primary standards are impractical. Secondary standards require more frequent standardisation due to their less stable nature.

      Volumetric Flasks


      Volumetric flasks are a type of laboratory glassware designed for the precise preparation of chemical solutions at a fixed volume. They are easily recognisable by their pear-shaped or round-bottomed body and long, narrow neck with a marked line to indicate a specific volume.

      Key Features of Volumetric Flasks

      • Marked Line: Each flask has a single, precise calibration line etched around the neck. When filled to this line, the flask contains the exact volume of liquid it is calibrated for, such as 100 mL, 250 mL, 500 mL, or 1 L.
      • Stopper or Cap: Volumetric flasks come with a stopper or cap to seal the flask, which is useful for mixing the solution without spillage.
      • Narrow Neck: The narrow neck assists in the precise control of the liquid level, making it easier to add liquid dropwise as the calibration line is approached.

      Comparison with Measuring Cylinders and Beakers

      • Measuring Cylinders: While measuring cylinders are also marked to indicate volume, they are generally less precise than volumetric flasks due to their wider diameter and less distinct volume markings. They are more suited for tasks where high precision is not as critical.

      • Beakers: Beakers are even less precise than measuring cylinders for measuring volumes. They are primarily used for mixing, stirring, and heating liquids rather than for accurate volume measurements. The wide mouth and lack of a precise volume mark make them unsuitable for preparing standard solutions where exact volumes are necessary.

      Making a Primary Standard Solution


      The preparation of a standard solution, particularly from a primary standard, is a meticulous process that involves the following steps:

      • Weighing the Primary Standard: Accurately weigh a precise amount of the primary standard using an analytical balance. The mass needed is calculated based on the desired concentration and volume of the standard solution. Remember that for a substance to be suitable for a primary standard solution, it should be available in solid state as this allows for accurate measurement.

      • Dissolving in Solvent: Transfer the weighed primary standard into a clean beaker, and add a specific solvent, usually distilled or de-ionised water (water of which typical ions are removed), to dissolve it. Swirl or stir the beaker to ensure complete dissolution. Tap water should be avoided during this step as it contains unwanted substances e.g. ions.

      • Quantitative Transfer: Transfer the solution from the beaker to a clean and appropriately sized volumetric flask. Use a clean funnel in the process. Use distilled water to rinse the beaker and the funnel, and discard the rinsing into the volumetric flask.



      • Diluting to Mark: Add more solvent (distilled water) until the solution's level reaches the calibration mark on the volumetric flask. This step ensures the solution has the exact desired volume, thereby guaranteeing its concentration.

      • Mixing: Invert the flask several times to homogenise the solution, ensuring uniform concentration throughout.

      Dilution of Standard Solutions

      Dilution is a process used to prepare a solution of lower concentration from a solution of higher concentration, and it's fundamental in creating standard solutions of various concentrations for analytical purposes. The dilution process follows the principle:

      where `c_1` and `c_2` are the initial and final concentrations, and `V_1` and `V_2` are the initial and final volumes, respectively.

      Steps for Dilution:

      1. Calculate Volume Needed: Use the dilution equation to determine the volume of the original solution required to achieve the desired concentration.

      2. Add Solvent: Transfer the calculated volume of the original solution into a new volumetric flask and add solvent up to the calibration mark.

      3. Mix Thoroughly: Ensure the diluted solution is well mixed to achieve uniform concentration.


      Example 1

      Prepare 250.0 mL of 0.100 mol/L NaCl solution.

      Example 2

      Dilute a 2.0 mol/L HCl stock solution to prepare 100.0 mL of a 0.500 mol/L HCl solution.