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Weight/Volume Percentage Concentration (w/v %)

Key Concepts

  • weight/volume percentage concentration is usually abbreviated as w/v (%)

  • w/v (%) = mass solute ÷ volume solution x 100

  • common units are g/100mL (%)

  • weight/volume is a useful concentration measure when dispensing reagents.

Weight/Volume Percentage Concentration Calculations

1. What is the weight/volume percentage concentration of 250mL of aqueous sodium chloride solution containing 5g NaCl?

  1. Calculate the weight/volume (%) = mass solute ÷ volume of solution x 100
        mass solute (NaCl) = 5g
        volume of solution = 250mL

    w/v (%) = 5g ÷ 250mL x 100 = 2g/100mL (%)

2. 10.00g BaCl2 is dissolved in 90.00g of water. The density of the solution is 1.09g/mL. Calculate the weight/volume percentage concentration of the solution.

  1. Calculate the volume of the solution: density = mass solution ÷ volume solution
        mass solution = 10g BaCl2 + 90g water = 100.00g
        volume solution = mass ÷ density = 100g ÷ 1.09g/mL = 91.74mL

  2. Calculate w/v (%) = mass solute ÷ volume solution x 100
        mass solute (BaCl2) = 10.00g
        volume solution = 91.74mL

    w/v (%) = 10.00 ÷ 91.74mL x 100 = 10.90g/100mL (%)

Conversion from Other Units

1. 2.0L of an aqueous solution of potassium chloride contains 45.0g of KCl. What is the weight/volume percentage concentration of this solution in g/100mL?

  1. Convert the units (mass in grams, volume in mL):
        mass KCl = 45.0g
        volume of solution = 2.0L = 2.0 x 103mL = 2000mL

  2. Calculate w/v (%) = mass solute (g) ÷ volume solution (mL) x 100
        w/v (%) = 45.0 ÷ 2000mL x 100 = 2.25g/100mL (%)

2. 15mL of an aqueous solution of sucrose contains 750mg sucrose. What is the weight/volume percentage concentration of this solution in g/100mL?

  1. Convert the units (mass to grams, volume to mL)
        mass solute (sucrose) = 750mg = 750 ÷ 1000 = 0.750g
        volume solution = 15mL

  2. Calculate w/v (%) = mass solute (g) ÷ volume solution (mL) x 100
        w/v (%) = 0.750g ÷ 15mL = 5.0g/100mL (%)

3. 186.4L of aqueous sodium hydroxide solution contains 1.15kg NaOH. What is the weight/volume percentage concentration of this solution in g/100mL?

  1. Convert the units (mass to grams, volume to mL)
        mass solute (NaOH) = 1.15kg = 1.15 x 1000 = 1,150g
        volume solution = 186.4L = 186.4 x 1000 = 186,400mL

  2. calculate w/v (%) = mass solute (g) ÷ volume solution (mL) x 100
        w/v (%) = 1,150g ÷ 186,400mL x 100 = 0.62g/100mL (%)

Reagent Volume-Mass Calculations

1. A student must add 1.22g of sodium chloride to a reaction vessel. The student is provided with an 11.78g/100mL (%) aqueous sodium chloride solution. What volume of this solution must be added to the reaction vessel?
  1. Re-arrange the equation: w/v(%) = mass solute (g) ÷ volume solution (mL) x 100
        volume solution (mL) = mass solute (g) ÷ w/v(%) x 100

  2. Subsitutue in the values:
        volume solution (mL) = 1.22g ÷ 11.78g/100mL x 100
        volume solution = 10.36mL

2. What is the mass in grams of potassium iodide in 14.86mL of a 32.44g/100mL aqueous potassium iodide solution?

  1. Re-arrange the equation: w/v(%) = mass solute (g) ÷ volume solution (mL) x 100
        mass solute (g) = w/v (%)/100 x volume solution(mL)

  2. Subsitutue in the values:
        mass KI = 32.44/100 x 14.86 = 4.82g


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