To compare the concentrations of some alkalis in saturated solutions.

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Arti Sodha

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Chemistry Planning Exercise

To compare the concentrations of some alkalis in saturated solutions.

Apparatus

25cm3 pipette

pipette filler

Conical flask

Burette

Stand

Saturated solution calcium hydroxide

Saturated solution sodium hydroxide

Saturated solution magnesium hydroxide

Saturated solution potassium hydroxide

Hydrochloric acid, various concentrations (see table)

Methyl orange indicator

Concentrations of acid used

To find the concentration of acid that was most appropriate to use, the solubility of the above hydroxides in water was found and converted into concentration of saturated in moldm-3  (see appendix A)1. A similar concentration of acid is used so that the volume of alkali used in the titration is reasonable.

Method

  • Pipette 25cm3 of 0.02 moldm-3 hydrochloric acid into a conical flask by using a pipette filler to fill the pipette up to the line and then emptying the pipette into a conical flask.
  • Add 3-4 drops of methyl orange indicator.
  • Pour the provided calcium hydroxide into the burette. Make sure the space beneath the tap is filled.
  • Add calcium hydroxide from the burette into the conical flask until the end point is reached; the methyl orange will turn from red to yellow. 2
  • Record the volume of calcium hydroxide used-this is the volume required to neutralize 0.02 moldm-3 hydrochloric acid.
  • Repeat until satisfactory replicates are obtained. (volumes 0.1 cm3 or less apart)
  • Repeat with each of the other alkalis, using the concentration of acid specified in the table.
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Risks and safety precautions

Wear safety goggles and a lab coat at all times to avoid any harm to the eyes and skin.

The acid and alkalis used are corrosive. If spilt, clean up immediately. If spilt on skin, wash thoroughly with cold water for 10-15 min.

The glassware used is very delicate and should be handled with great care. If any glass is broken, it should be reported and swept up immediately.

To show how calculations are carried out to find the concentration of saturated solution of the hydroxide

Table of suggested volumes of alkali ...

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