Molarity is a measure of the concentration of solute in a solution. It can be expressed as moles of solute ÷ volume of solution: c = n ÷V where: c - concentration of solute, n - moles of solute V - volume of solution
n can be expressed as: <span>n = m ÷ Mr </span>where: <span>n - moles of solute </span>m - mass of solute Mr - relative molecular mass
a. We know volume: V = 289.2 mL = 0.2892 L We need n and c.
n = m ÷ Mr m = 15.4 g Mr (<span>KCl) = 74.55 g/mol n = </span>15.4 g ÷ <span>74.55 g/mol n = 0.206 mol</span>
Thus, c = 0.206 mol ÷ <span>0.2892 L c = 0.712 mol/L = 0.712 M
</span>b. We know volume: V = 0.614 L We need n and c.
n = m ÷ Mr m = 14.4 g Mr (CaCl₂<span>) = 110.98 g/mol n = </span>14.4 g ÷ <span>110.98 g/mol n = 0.129 mol</span>
Thus, c = 0.129 mol ÷ <span>0.614 L c = 0.210 mol/L = 0.210 M </span> c. We can use formula: m₁V₁ = m₂V₂ <span>m₁ = 3 M </span><span>V₁ = 28 mL= 0.028 L </span><span>m₂ = ? </span><span>V₂ = 0.250 L </span>Thus: 3 M × 0.028 L = m₂× <span>0.250 L </span> m₂ = 0.336 M
