Arti Sodha
Words-750 approx
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.