At the end of this lesson, students should be able to: a)State the meaning of concentration and b) State the meaning of molarity correctly. c) State the relationship between the number of moles with molarity and volume of a solution.
• The quantity of solute in a given volume of solution. Which is usually a dm3. 3 mass of solute ( g ) Concentration ( g dm ) volume of solution (dm3 )• Unit: g dm-3• 1 dm3 = 1L= 1000 cm3 = 1000 mL
• The number of moles of solute that are present in 1 dm3 of solution. 3 number of moles of solute (mol ) Molarity (mol dm ) volume of solution (dm3 )• Unit : mol dm-3
Molar mass Molarity Concentration(mol dm-3) (g dm-3) Molar mass
Number of moles of solute,n molarity ( M ) volume of solution (V )
EXAMPLE 1Calculate:a) The concentration of solutionin g dm-3 when 6.00 g of copper (II) sulphate is dissolved in water to form 500 cm3 solution.b) The molarity of solution when 0.8 mol of sodium hydroxide is dissolvedin distilled water to form 250 cm3 of solution.
SOLUTION 1a) Mass of copper (II) sulphate = 6.00 g volume of solution = 500 cm3 = 0.5 dm3 Concentration = 6.00 g/0.5 dm3 = 12 g dm-3b) Number of moles of NaOH = 0.8 mol volume solution = 250 cm3 = 0.25 dm3 molarity of NaOH = 0.8 mol/ 0.25 dm3 = 3.2 mol dm-3
EXAMPLE 2Calculate: What is the mass of potassium hydroxide required to dissolve in water to prepare a 200 cm3 solution that contains 30 g dm-3? Answer: 6 g
EXAMPLE 3Calculate: 0.2 mole of sodium carbonate is dissolved in water to produced a solution with concentration of 0.5 mol dm-3. What is the volume of sodium carbonate solution? Answer: 400 cm3
EXAMPLE 4Calculate: A copper (II) sulphate solution has a concentration of 40.0 g dm-3. What is the molarity of this solution in mole dm-3? [relative atomic mass: O,16; S,32; Cu,64] Answer: 0.25 mol dm-3 of CuSO4
EXAMPLE 5Calculate:The concentration of dilute hydrochloric acid in areagent bottle is 2.0 mol dm-3a) What is the concentration of this solution in g dm-3?b) Find the mass of hydrogen chloride in 250 cm3 of the hydrochloric acid? [relative atomic mass: H,1;Cl,35.5]
EXAMPLE 6Calculate the number of moles of sodiumhydroxide in 25.0 cm3 of 1.5 mol dm-3aqueous sodium hydroxide. answer: 0.0375 mol
EXAMPLE 7A 0.5 mol dm-3 potassium hydroxide solutioncontains 7.0 g potassium hydroxide. Calculate thevolume of this solution.[relative atomic mass: H,1; O,16; K,39] answer: 0.25 dm3 / 250cm3
At the end of this lesson, students should be able to: a)Describe methods for preparing standard solutions. b)Describe the preparation of a solution with a specified concentration using dilution method. c) Relate pH value with molarity of acid and alkali. d)Solve numerical problems involving molarity of acids and alkalis.
A standard solution is a solution where its concentration is accurately known. Prepare 100 cm3 of sodium hydroxide solution with a concentration of 0.5 mol dm-3 1. Molecular mass? [Na,23;O,16;H,1] 2. Mass of NaOH? 3. Prepare solution.
Prepare 100 cm3 of sodium hydroxide solution with aconcentration of 0.5 mol dm-3Solution:Volume (V) = 100cm3 =0.1 dm3Molarity (M) = 0.5 mol dm-3Mass =?Molar mass NaOH:= 23+16+1 = 40 g mol-Mole = mass/Molar mass
Mole (n) = Molarity (M) X Volume (V) n = 0.5 mol dm-3 X 0.1 dm3 n = 0.05 mol n = mass/molar mass mass = n x molar mass mass = 0.05 mol x 40 g mol- mass = 2.0 g
2.0 g of NaOH is weighed NaOH poured into a beaker Containing distilled water
process of diluting a concentrated solution byDilution adding water to get a more dilute solution. M1 V1 = M2V2 M1: molarity of the solution before water is added V1 : Volume of the solution before water is added M2: molarity of the solution after water is added V2 : Volume of the solution after water is added
Example :90 cm3 of distilled water is added to 10 cm3 of a 1.0mol dm-3 solution of HCl. Determine the molarity ofthe diluted solution 0.1 mol dm-3
Prepare 500 cm3 of a 0.5 mol dm-3 ofHydrochloric acid solution from 2.5 mol dm-3 ofHCl solution. 1. Calculate the volume of solution before dilution? (V1) 2. The solution before dilution poured into 500 ml volumetric flask. 3. Water is added until reached graduation mark. 4. Close with stopper, then shake it.
The higher the The higher themolarity of acid, molarity of an alkali, the higherthe lower the pH the pH value. value.
Example :500cm3 of a solution that contains 2.0 mol sodiumhydroxide is added to 1500cm3 of a solution that contains4.0 mol sodium hydroxide. Calculate the molarity of thesodium hydroxide solution produced.