How to dilute solutions accurately and safely

10 August 2016

How to dilute solutions accurately and safely

Using a concentrate and diluting at the point of use is a great way to save on storage space and transport costs, and also allows you to vary the concentration at each use, making up to exactly the concentration you need.

This can be a quick task when you know how, but it’s important to remember a few key points to ensure your dilutions are performed accurately and safely. These same points hold true in the lab and in industrial settings.

Use our 5 golden rules below to remind yourself of the important factors before you start a dilution.

1. Calculate before you start

Much like the old carpenter’s adage “measure twice, cut once!”

Make sure that you have calculated how much of the concentrate and the dilution liquid you need before you begin. Double check your calculations to avoid wasting time and materials.

We like to use the dilution equation;

C1 x V1 = C2 x V2

Though there are many online calculators to help with dilution calculations if you are unsure.

If you are working to a pre-written procedure make sure to read it through before you begin.

2. Know your solutions!

Check the safety advice on the solutions given on the MSDS, particularly on the concentrate.

  • Should PPE such as gloves, goggles or protective clothing be worn?
  • Is the concentrate strong enough to give off fumes, does a fume hood or extractor need to be used?
  • Are the concentrate and dilution liquid safe to mix?
  • Is there a risk assessment or work method in place which you must follow?

3. Measure Accurately

Ensure that when you measure out the concentrate and the dilution liquid these are done accurately and to the correct, calculated values. Again, double check!

The method of measuring will vary depending on the scale you’re working at and the accuracy you require, but make sure the measurement is as accurate as you can be with the equipment you have.

As a rough guide;

  • For micro volumes (microlitres, µL to around 2ml) a micropipette can be used
  • For small ml volumes (1ml to approx. 100ml) a volumetric pipette can be used
  • For ml to L (approximately 5ml to around 2L) a volumetric flask can be used
  • For larger L’s volumes – choose a solution that suits the work site and the liquids. Either a pump or weighing scale might be used.

4. ALWAYS add the concentrate to water

Whether you are using highly concentrated acid or base, you should always add the concentrate to the water.

This is because when two solutions mix, heat is generated (due to the heat of dilution).

The extra heat going into the concentrated acid or base could cause it to give off vapours or even boil, which may be extremely dangerous.

Water has a very high tolerance for absorbing heat, so adding the concentrate to the water will allow the water to act as a “heat sink” absorbing it safely. Some methods may need you to use an extra heat sink, such as an ice bath around the vessel you’re diluting in.

Make the addition slowly, mixing and observing the temperature as you add to ensure it’s kept under control.

5. And finally, check your results!

After the dilution is complete, you should still check that it is correct – measuring the pH is often the simplest way to do this, is it the right value you would expect?

Remember that these points are simply a guideline, the procedure for your dilution might vary depending on the liquids, the volumes, the environment and the accuracy you need.

There is no alternative for knowing your chemicals and task well, so make sure you understand the job and the risks present before you begin.

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