Determining the Solubility of Calcium Hydroxide.

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Matt Harris                Determination of the Solubility of Calcium Hydroxide

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Determining the Solubility of Calcium Hydroxide

Introduction

Calcium Hydroxide Ca(OH)2 dissolves only slightly to form an alkaline solution. This is a saturated solution often called limewater. The solubility of the calcium hydroxide can be found by titrating the saturated solution against a solution of an acid whose concentration is known.

I will be using a sample of limewater, containing approximately 0.015 mol dm-3 of calcium hydroxide, and a solution of Hydrochloric Acid, whose concentration is 0.3 mol dm-3.

Choosing an Indicator

The indicator I must use in this titration will depend on the strength of the acid and alkali I use.

I will be using Calcium Hydroxide and Hydrochloric Acid. These are a strong alkali and acid respectively.

This means I must use an indicator compatible with a strong alkali and strong acid. The 2 indicators I may use are Phenolphthalein and Methyl Orange. I have elected to use Methyl Orange. The colour change I am expecting is;

Yellow                                 Red

                                                        (Alkali)                                              (Acid)Method

*The end point can be determined by a clear colour change in the solution. This colour change will be Yellow to Red.

The reaction is:


To ensure maximum accuracy, the following steps should be taken:

  1. When performing the titration, a white tile should be placed under the conical flask, to make the colour change abundantly clear.
  2. The experiment should be repeated until 3 values for the end-point agree to 1 decimal place, in addition to the rough titration.
  3. Each endpoint value should be read to 2 decimal places.
  4. The end-point value should be read from the bottom of the meniscus to show the true value.
  5. The funnel should be removed from the top of the burette before the titration is started to ensure that no drops of Hydrochloric Acid are added to the solution.
  6. There must be no air bubbles anywhere in the burette during the titration.
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If these steps are followed, the titration should be as accurate as possible, given the margin for error in reading values from the burette and volumetric flask.

Safety Precautions

To ensure the experiment is carried out safely, certain safety procedures should be adhered to.

HYDROCHLORIC ACID – Corrosive, Irritant

Wear eye protection and gloves at all times when using HCl

If spilt in eyes: Immediately rinse eyes with clean, distilled water for at least 15 minutes. Lift eyelids to ensure eyes are thoroughly flushed. Do not attempt to neutralise the acid. Seek medical opinion.

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