Concentration Chemistry Example 2

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Example 2

medium
How many grams of KOH are needed to prepare 250 mL250\,\text{mL} of a 0.40 M0.40\,\text{M} solution? (KOH = 56.11 g/mol56.11\,\text{g/mol})

Solution

  1. 1
    Convert the volume to liters and find the required moles: n=MV=0.40 mol/L×0.250 L=0.100 moln = MV = 0.40\,\text{mol/L} \times 0.250\,\text{L} = 0.100\,\text{mol}.
  2. 2
    Use the molar mass to convert moles to grams: m=n×Mmolar=0.100×56.11m = n \times M_{\text{molar}} = 0.100 \times 56.11.
  3. 3
    Evaluate the product: m=5.61 gm = 5.61\,\text{g} of KOH.

Answer

5.61 g of KOH5.61\,\text{g of KOH}
This is the standard procedure for preparing a solution of known concentration: calculate the required mass, dissolve it, and dilute to the exact volume.

About Concentration

The quantity of solute dissolved per unit volume of solution, most commonly expressed as molarity (MM) in units of moles per liter (mol/L).

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