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Control of Normality
Take a 10 ml of sample from the 4.0 N sodium hydroxide container. Add 2-3 drops phenolphthalein and just
enough 1.0 N hydrochloric acid until it turns clear. If the normality is correct, 40 ml of 1.0 N hydrochloric acid
will neutralize 10 ml of 4.0 N sodium hydroxide.
Mixing Procedure for the preparation of 4.0 N Sodium Hydroxide solution, from 100% Sodium
Hydroxide pellets:
1. Use deionized water, free from organic and inorganic carbon. The conductivity of the deionized water
used should be less than 0.5 µS/cm.
2. Fill 80% of the container with deionized water.
3. Blow through the deionized water with a CO
2
free gas such as Nitrogen or Oxygen, to purge the water
of any dissolved CO
2
.
4. a) In order to prepare 1 liter of 4.0 Normal base solution, add 160 grams of 100% purity sodium
hydroxide pellets. Mix gently and add more deionized water to make it exactly 1 liter.
b) To prepare a 25 liters base solution, add 4000 grams of 100% purity sodium hydroxide pellets in
stages. Adding the sodium hydroxide pellets in stages will prevent the solution from heating up.
Gently mix to dissolve the sodium hydroxide pellets and then add more deionized water to make it
exactly 25 liters.
5. Seal the container.
6. Gently shake the container to mix the base
with the water.
7. Allow the container to stand for one hour, and gently shake again to ensure a good mix.
If the base reagent is not mixed fully, then a highly concentrated layer will form in the
bottom of the container. As the BioTector takes the base from the bottom of the
container, this may create problems during operation, as the base will be too strong
relative to the acid. Always mix the base solution for a second time, about 1 hour after it
has been manufactured to ensure that it is completely mixed.
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