Chemistry

Session Opener

Session Objectives Problems related to 1. Mole concept 2. Stoichiometry

Simple Titrations Find out the concentration of a solution with the help of a solution of known concentration. For mixture of two or more substances N 1 V 1 + N 2 V 2 + ……= NV Where V=(V 1 + V 2 + …..)

Normality of mixing two acids Normality of mixing acid and bases

Questions

Illustrative example 1 Find the molality of H 2 SO 4 solution whose specific gravity(density) is 1.98 g/ml and 95% mass by volume H 2 SO ml solution contains 95 g H 2 SO 4. Moles of H 2 SO 4 = Mass of solution = 100 × 1.98 = 198 g Mass of water = 198 – 95 = 103 g Molality == m Solution: Molality =

Illustrative example 2 A sample of H 2 SO 4 (density g/ml) is 86% by mass. What is molarity of acid? What volume of this acid has to be used to make 1 L of 0.2 M H 2 SO 4 ? Let V 1 ml of this H 2 SO 4 are used to prepare 1 L of 0.2 M H 2 SO 4.M 1 V 1 = M 2 V × V 1 = 0.2 × 1000 Solution:

Illustrative example 3 A mixture is obtained by mixing 500ml 0.1M H 2 SO 4 and 200ml 0.2M HCl at 25 0 C. Find the normality of the mixture. For the mixture, Solution:

Illustrative example ml 0.2 N HCl is neutralized with 250 ml 0.2 N NaOH. What is the strength of the resulting solution? Equivalents of HCl Equivalents of NaOH Equivalence of excess HCl Normality of HCl (excess) Strength of HCl =.067 × 36.5 g/litre = 2.44 g/litre Solution:

Solution N = 2.44 N Strength of HCl =.067 × 36.5 grams/litre = 2.44 grams/litre Normality of HCl (excess),

Illustrative example 5 Calculate the empirical formula of a mineral having the following composition CaO=48.0% ;P 2 O 5 =41.3% ; CaCl % /56= /142= /111= CaO P 2 O 5 CaCl 2 Simple ratio Mol. Mass %tageConstituents

Illustrative example g of an impure sample of sodium sulpate dissolved in water was treated with excess of barium chloride solution when 1.74 g of BaSO 4 were obtained as dry precipitate. Calculate the percentage purity of the sample.

Illustrative example 7 A solid mixture weighing 5.00 g containing lead nitrate and sodium nitrate was heated below C until the mass of the residue was constant. If the loss of mass is 28%, find the mass of lead nitrate and sodium nitrate in the mixture.

Solution

Illustrative example 8 What volume of oxygen is required to effect complete combustion of 200 cm 3 of acetylene and what would be the volume of CO 2 formed?

Illustrative example 9 The formula weight of an acid is 82.0 in a titration.100 cm 3 of a solution of this acid containing 39.0 g of the acid per litre were completely neutralised by 95.0 cm 3 of aqueous NaOH containing 40.0 g of NaOH per litre. What is the basicity of the acid? Let requirement wt. of acid =E Solution:

Solution

Illustrative example 10 Calculate approximate molecular mass of dry air containing 78% N 2 and 22% O 2. Solution:

Illustrative example 11 Calculate atomic mass of element X and Y given that Composition of X=9.76% Relative no. of atoms of X=0.406 Composition of Y=26.01 Relative no. of atoms of Y=1.625 Solution:

Illustrative example 12 The molality of a solution of ethyl alcohol (C 2 H 5 OH) in water is 1.55m.How many grams of ethyl alcohol are dissolved in 2kg of water? Solution:

Illustrative example 13 You are given 1 litre of 0.15 M HCl and 1 litre of 0.40 M HCl. What is the maximum volume of 0.25 M HCl which you can make from these solutions without adding any water? Solution: Volume of 0.25 M HCl can’t be more than 2 litres because no water is added

Illustrative example 14 How many ml of H 2 SO 4 of density 1.8 g/ml containing 92.5% by volume of H 2 SO 4 should be added to 1 litre of 40% solution of H 2 SO 4 ( density 1.30 g/ml) in order to prepare 50% solution of H 2 SO 4 (density 1.4 g/ml).

Solution

Illustrative example 15 Gastric juice contains about 3.0 g of HCl per litre. If a person produces about 2.5 litre of gastric juice per day, how many antacid tablets each containing 400 mg of Al(OH) 3 are needed to neutralize all the HCl produced in one day? Solution:

Illustrative example 16 Calculate the number of Cl – ions in 100 ml of M HCl solution. Solution: HCl is a strong acid, it ionises completely Conc. of HCl is equal to that of Cl – ions

Helena kabr se farar Group 1 elements (Alkali metals) He Li Na K Rb Cs Fr

Be Mg Ca Sr Ba Ra Bear mugs can serve bar rats Group 2 elements (Alkaline earth metals)

B Al Ga In Tl Bob Allen Gave Indians Tennis Lessons Group 13 elements (Boron family)

C Si Ge Sn Pb Can sily or Genius snatch lead Group 14 elements (Carbon family)

N P As Sb Bi Never put arsenic in silver bullet bear Group 15 elements (Nitrogen family)

O S Se Te Po Oh, she sells tie Poles Group-16 elements (Oxygen family)

F Cl Br I At Fat Clyde bribed Innocent Atul Group-17 elements (Halogen family)

Group-18 elements (The Noble Gas) He Ne Ar Kr Xe Rn He needs our crazy Xerox repairman

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