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Wednesday, 23 April 2014

PREPARATION OF 50% KOH

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PREPARATION OF 50% KOH

50% KOH contains 50%w/w potassium hydroxide and for 40g of the compound is containd in every 100ml of its solution.

Potassium hydroxide are  made as solid deliquescence  pellets.

Deliquescence substances are chemical compound that tend to absorb so much water from the atmosphere that they dissolve in it to form an aqueous solution of the compound.

50%w/w KOH contains 8.93M KOH

10M KOH= 10NKOH

From

Molar Mass of each element K=39, O=16, H=1

Molar Mass of NaOH= 39+16+1

                                 =56g

Number of Mole=  Mass

                                    Molar mass

From

50% KOH

The mass of KOH in 100ml of it solution is 50g

Thus

Number of Mole of KOH =       Mass

                                                            Molar mass

Number of Mole of NaOH =       50
                                                            56

                                                   =  0.893mole

In 1000ml or 1liter of the KOH

Molar Concentration =              Mass                 X  1000

                                                      Molar mass          Volume

or

Molar Concentration =              Number of mole                    X  1000

                                                                                                             Volume

Molar Concentration =              50                      X  1000

                                                       56                           100

Molar Concentration =                 8.93M

Or

Since the number of mole of 50% KOH in 100ml of the solution  is 1mole

Therefore

Molar Concentration =              0.893                X  1000

                                                                                         100

Molar Concentration =              8.93M

Preparation Procedure

1.     Make available an accurate analytical weighing balance, clean dry 500ml beaker, distilled/deionized water, stirrer, 1000ml Volumetric flask and Spatula

2.     Place the beaker on the balance and tare/zero the reading

3.     With the aid of the spatula weigh 400g of the KOH pellet into the clean beaker

4.     Add about 400ml of distilled/deionized water and stir to dissolve the pellets in a cold water bath (Note: the reaction is exothermic because heat will be given up thereby causing increase in the temperature of the beaker, ensure you stir gently in the cold water bath)

5.     When all the pellets have dissolved, transfer the solution into the 1000ml volumetric flask. Allow to cool

6.     Add distilled/deionized water to the mark, shake and allow to cool

7.     On cooling decrease in volume of the solution will be noticed, add distilled/deionized water again to the mark and shake.

Note:

1.     KOH has high affinity for water thus this is why there is decrease in the solution after making up to the mark

2.     Due to the high affinity for moisture in the atmosphere the weighing should be done in vacuum or less aerated place at a fast speed.

3.     Deionized water is best for the preparation of this solution because of it lack of ions, which when present can interfere with the KOH in the solution.

 

 

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