Molarity of 45% Potassium Hydroxide (KOH)

Molarity of 45% Potassium Hydroxide (KOH)

Overview:

  • Potassium Hydroxide (KOH) is a clear colourless liquid. A 45% (w/w) concentrated Potassium Hydroxide can be obtained from different suppliers.
  • 45% (w/w) Potassium Hydroxide means that 100 grams of Potassium Hydroxide contains 45 grams of KOH.
  • The density of 45% (w/w) Potassium Hydroxide is 1.456 g/ml at 25°C that means that weight of the 1 ml of Potassium Hydroxide is 1.456 gram at 25°C.
  • Molarity refers to number of moles of the solute present in 1 litre of solution.
  • In simple words, 1 mole is equal to atomic weight of the substance. For example, 1 mole of KOH is equal to 56.11 grams of KOH (molecular weight = 56.11).

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Calculation procedure:

Known values:
Density of Potassium Hydroxide :                             1.456 g/ml
Molecular weight of KOH:                                         56.11 g/mole

Concentration of Potassium Hydroxide:            45% (% by mass, wt/wt)

Step 1: Calculate the volume of 100 grams of Potassium Hydroxide.

Formula:
Density =  weight / volume    or
Volume =  weight / density    or

Volume of 100 gram of Potassium Hydroxide : 100/1.456 =  68.6813 ml

Note: 45% (w/w) Potassium Hydroxide means that 100 grams of Potassium Hydroxide contain 45 grams of KOH.

The volume of 100 grams of Potassium Hydroxide is 68.6813 ml. That means 45 grams of KOH is present in 68.6813 ml of Potassium Hydroxide.

Step 2: Calculate how many grams of KOH is present in 1000 ml of Potassium Hydroxide.

68.6813 ml of Potassium Hydroxide contain       = 45 grams of KOH
1 ml of Potassium Hydroxide will contain           = 45/68.6813 grams of KOH

1000 ml of Potassium Hydroxide will contain     = 1000 x 45/68.6813 = 655.2 grams of KOH

1000 ml of Potassium Hydroxide will contain 655.2 grams of KOH

Step 3: Calculate number of moles of KOH present in 655.2 grams of KOH.

56.11 grams of KOH is equal to 1 mole.
1 gram of KOH will be equal to 1/56.11 moles.

655.2 grams will be equal to = 655.2 x 1/56.11 = 11.677 moles

Therefore, we can say that 1 litre of Potassium Hydroxide contains 11.677 moles or in other words molarity of 45% (w/w) Potassium Hydroxide is equal to 11.677 M.