Lecture 6 – Moles, Solutions & Percentage Yield

Moles & Solutions:

Solutions are formed by the dissolving of a solid called SOLUTE in a liquid that does the dissolving called SOLVENT. Concentration of the solutions depends on the amount of solid dissolved in the solvent.

Units: 

Titration:

Titration is defined as a reaction between an acid and an alkali to form a salt and water. This is a Qualitative Technique and the end point is determined using an indicator.

Formula # 6:

Example:

Calculate the volume of 1 mol/dm³ sodium hydroxide required to completely neutralize 12.5cm³ of sulphuric acid having a concentration of 1 mol/dm³.

Equation:

Acid:

M = 1 mol/dm³

V = 12.5cm³

n = 1

Alkali:

M = 1 mol/dm³

V = ?

n = 2

V_alkali = 2 x 12.5cm³ = 25cm³

Note: Since the acid is dibasic in nature (i.e. each Molecule of H₂SO₄ contains 2 H⁺ ions), the volume of the base required is twice, when their concentrations are same.

Percentage Purity:

Percentage Purity is defined as the purity if the chemical depending on their method of preparation.

Example NaCl:

NaCl = NaCl = 99%

            Sulphate < 0.05%

            Iodide & Bromide < 0.01%

            Arsenic < 0.0001%

            Lead < 0.0005%

            Iron < 0.001%

Percentage Yield:

Consider the following reaction:

Decomposition of Calcium carbonate:

100g of CaCO₃ gives 56g of CaO and 44g of CO₂

100g of CaCO₃ on decomposition should produce 56g of CaO actually/mathematically/theoretically; 

But experimentally only 42g is obtained.

Percentage Yield is given by:

Formula # 7: 

The percentage yield of CaO for this reaction is

Percentage yield is the measure of the efficiency and extent of the reaction. It is affected by factors such as temperature, pressure, purity of the substance and presence of a catalyst.