**Show that the mass of sodium hydroxide that would be present in 100 L of the waste water is 342 g.**

The concentration of sodium hydroxide in waste water from an alumina refinery was found by titrating 20.00 mL aliquots of waste water against 0.150 M hydrochloric acid, using phenolphthalein as indicator. The average titre of several titrations was 11.40 mL.

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The basic relationship you need to use is:

La*Ma = Lb * Mb

Where:

La = liters of acid

Lb = liters of base

Ma = molarity of acid

Mb = molarity of base.

Use your data to solve for the molarity of the base.

The molarity of the base tells you how many moles of base (NaOH) are in one liter. But you have 100 liters. So multiply your answer by 100 to get the number of moles of NaOH in 100 L.

To convert moles to mass, find the formula mass of NaOH and multiply by the number of moles of NaOH you found in the 100 L and you have your answer.

**Sources:**

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