Concentration

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• Concentration refers to the amount of solute dissolve in the solvent.
• We can use many kinds of units to describe how much solute we have in a solvent.

Quantifying Concentration

• Concentration can be given in a range of different units:
• Mass per 100g water (% w/w)
• Volume per 100 mL water (% v/v)
• Mass per 100mL water (%w/v)
• Parts per million (ppm) – mg per kg
• Moles per litre of solution (mol $L^{-1}$)
  • This is sometimes called molarity.

Calculations

v/v % (when solute is a liquid)

$\frac{V_{solute}}{V_{solvent}}\times 100\%$

• mL per 100 mL, or mL/100mL

m/v % (when solute is a solid)

$\frac{m_{solute}}{V_{solvent}}\times 100\%$

• g per 100 mL, or g/100mL

m/m % (when both solute and solvents are solids)

$\frac{m_{solute}}{m_{solvent}}\times 100\%$

• g per 100 g, or g/100g

Density

• Sometimes we have to convert volume of solution into mass of solution. Use value of density if such provided to do the calculations.
• $Mass=Density\times Volume$
• $Density=\frac{Mass}{Volume}$

Parts per Million

• As a ratio:  parts per million (ppm)
• $Ppm=\frac{mas{s}_{solute}}{mas{s}_{solvent}}$
• Mass of solute is in mg, mass of solvent in kg

Molarity

• mol/Litre, a.k.a. $mol{L}^{-1}$
• Also known as molarity, M

$C=\frac{n}{V}$

• V is in Litres

Grams Per Litre

• g/litre $\frac{m}{V}$
• V is in Litres, m is in grams