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To compare the concentrations of some alkalis in saturated solutions.

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Introduction

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. Name of Alkali Concentration of saturated solution / moldm-3 Concentration of hydrochloric acid used / moldm-3 Calcium hydroxide 0.020 0.03 Sodium hydroxide 0.27 0.20 Magnesium hydroxide 0.00015 0.00020 Potassium hydroxide 0.20 0.20 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. ...read more.

Middle

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 required to neutralize the acid Alkali Suggested volume alkali required to neutralize the HCl / cm3 Volume of hydrochloric acid used / cm3 Concentration of acid used / moldm-3 Calcium hydroxide 18.7 25 0.02 Sodium hydroxide 18.5 25 0.20 Magnesium hydroxide 16.7 25 0.00020 Potassium hydroxide 25.0 25 0.20 To calculate concentration of calcium hydroxide Ca(OH)2 (aq) + HCl (aq) --> CaCl2 (aq) ...read more.

Conclusion

+ H2O (l) 1 mol KOH --> 1 mol HCl 1 mole = (25 x 0.20) / 1000 = 0.005 mol Number of moles KOH = 0.005 mol Thus concentration= (1000 x 0.005) / 25.0 = 0.20 moldm-3 Appendix A The solubility in water (100 x the mass of anhydrous solute per unit mass water) was found using Chemistry data book JG Stark HG Wallace Second edition 1982 p62 The concentration in water in gdm-3 was found by dividing by 100 to give the solubility of the anhydrous salt per 1 g water, and then multiplying by 1000 to give the solubility per dm-3 water. The concentration in moldm-3 was found by dividing the concentration in gdm-3 by the relative atomic mass. Hydroxide Solubility in water (100 x the mass of anhydrous solute per unit mass water) Concentration in water (gdm-3) Relative atomic mass Concentration in water (moldm-3) Calcium hydroxide 0.156 1.56 74.1 0.02 Sodium hydroxide 109 10.9 40 0.27 Magnesium hydroxide 0.0009 0.009 58.3 0.00020 Potassium hydroxide 112 11.2 56.1 0. ...read more.

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