The Solutions Equation

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Solutions
A solution is a homogeneous mixture of two or more substances in which the proportions of
the substances are identical in the mixture.
The major component of a solution is called a solvent and minor ones are called solutes.
The amount of solute present in a fixed quantity of solvent or solution is called the
concentration of the solution. It is usually measured in grams of solute per dm3 of solution or
in moles of solute per dm3 of solution. In the latter case (moldm-3) it is also known as the
molarity of the solution.
The number of moles of solute, molarity of the solution and volume of solution can thus
be related by the equation:
Number Of Moles = Volume x Molarity
N= CV/1000
The volume of solution in this case must always be measured in dm3 (or litres). If the
volumes are given in cm3 then V/1000 must be used instead.
28.3 cm3 of a 0.10 moldm-3 solution of NaOH was required to react with 25 cm3 of a solution
of H2SO4. What was the concentration of the H2SO4 solution?
Equation: H2SO4 + 2NaOH Na2SO4 + 2H2O
Moles of NaOH = 28.3/1000 x 0.1 = 2.8 x 10-3
2:1 ratio so moles of H2SO4 = 2.8 x 10-3/2 = 1.4 x 10-3
so concentration of H2SO4 = 1.4 x 10-3/25 x 1000 = 0.056 moldm-3.
Calculate the volume of 0.50 moldm-3 nitric acid required to react completely with 5 g of lead
(II) carbonate.
Equation: PbCO3 + 2HNO3 Pb(NO3)2 + CO2 + H2O
Moles of PbCO3 = 5/267 = 0.0187
1:2 ratio so moles of HNO3 = 0.0187 x 2 = 0.0375
Volume of HNO3 = 0.0375/0.5 x 1000 = 74.9 cm3.

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