Standard solution

• Standard solution


  A solution whose concentration is known accurately
• Important factors for concentration

  • Concentration is usually given in mol/dm-3
  • The correct mass of substance is accurately measured
  • Successfully transferred to the volumetric flask used to make up the solution
• Primary standard should

  • Solid with high molar mass
  • Available in a high degree of purity
  • Chemically stable
  • Does not absorb water from the air
  • Soluble in water
  • react rapidly and completely with other substances when used in a titration
• Concentration


  It can be expressed by number of moles per dm3 or number of grams per dm3
• A standard solution is made by dissolving the substance to be tested into water or dilute acid.
• Weighing the required mass of substance


  1. Take a weighing boat and place it on the balance

  2. Set the balance to 0 or weigh by difference

  3. Carefully weigh the required mass of substance
• Labelling the solution


  Label the solution with your name, the date, and the contents (e.g., 0.0987 mol/dm-3 NH2SO3H)
• Transferring the solution to the volumetric flask

  1. Stir with a glass rod until all the solid is dissolved

  2. Transfer the solution to the volumetric flask using a funnel and a glass rod to allow the entire substance to be added with minimal loss

  3. Rinse out the beaker, glass rod, and funnel at least twice with water from the wash bottle and add it to the volumetric flask each time to prevent any loss of substance that could have remained on the glass rod or beaker
• Dissolving the substance

  1. Transfer the amount to a beaker

  2. Add deionised/distilled water from a wash bottle to dissolve it

  3. Rinse all the substance off the watch glass at least twice to prevent any loss of substance that could have remained on the weighing boat
• Calculations before the experiment

  1. Number of moles needed to make up a solution with the required volume and concentration

  2. Relative formula mass (Mr) of the chosen substance

  3. The mass of substance needed using answers in part 1 and 2
• Filling the volumetric flask

  1. Add water to just below the line on the volumetric flask

  2. Add the final drops with a teat pipette to ensure that the bottom of the meniscus is on the line

  3. Put the lid on the flask and turn the flask over a couple of times to mix the solution
• Standard solution calculation:

  • molar mass of base (sodium carbonate e.g)
  • amount of sodium carbonate used (mass/molar mass = amount)
  • concentration of sodium carbonate (n/v)