- The concentration of a solution tells you how much solute is dissolved in 1 unit volume of solution.
- The volume of a solution is measured in dm³ (litres). 1 dm³ = 1000 cm³.
- The amount of solute can be measured in grams or moles.
- 2 units of concentration used in chemistry are g dm
^{-3}and mol dm^{-3}

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Concentration in g dm^{-3}

- Concentration is the number of moles of solute per liter of solution.
- A concentration of 10 g dm
^{-3}means there is 10 g of solute dissolved in1 dm^{3}of solution.

**Example 1**:

Calculate the concentration of the solution if 28g of NaOH is dissolve in 250cm

^{3}of water.

**Answer**:

Mass of solute = 28g

Volume of solvent = 250cm³ = 0.25dm³

$$\begin{array}{l}Concentration=\frac{Mass}{Volume}\\ \frac{{}^{}}{}\\ =\frac{28g}{0.25d{m}^{3}}=112g/d{m}^{3}\end{array}$$

###
Concentration in mol dm^{-3} (Molarity)

- Molarity is probably the most commonly used unit of concentration. It is the number of moles of solute per liter of solution.
- A concentration of 2 mol dm
^{-3}means there are 2 moles of solute dissolved in 1 dm^{3}of solution.

**Example**:

What is the molarity of a solution made when water is added to 0.2 mol of CaCl

_{2}to make 100 cm³ of solution? [RAM: Ca = 40; Cl = 35.5]

**Answer**:

Number of mole of solute = 0.2 mol

Volume of solvent = 100 cm³ = 0.1 dm³

$$\begin{array}{l}\text{Molarity=}\frac{\text{NumberofMole}}{\text{Volume}}\\ =\frac{0.2mol}{0.1d{m}^{3}}=2mol/d{m}^{3}\end{array}$$

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