Titration

This is a method of volumetric analysis in which a solution (usually a standard solution) is added from a burette to another solution (usually whose concentration is unknown) until the reaction is complete. An indicator changes color immediately the reaction is complete or when the end point is reached. Most titrations at this level are acid-base titrations.

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N.B The first titration is regarded as a trial run (rough titration) and may not be very accurate, therefore the value may not be used in computing the average volume. Values used in calculating the average volume must be close to each other

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=51.5%

Calculating number of moles of water of crystallization

The water of crystallization present in compounds does not take part in the reaction

  1. Calculate the number of moles of water of crystallization in oxalic acid crystals, H2C2O4.xH2O from the following data.
    5.0g 0f the crystals were made up to 250cm3 of aqueous solution and 25cm3 of this solution required 15.9 cm3 of 0.5M NaOH solution to neutralize it.
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Calculating basicity of acids
Basicity of an acid is the number of hydrogen ions that can be produced by one molecule of the acid upon complete ionization. It is not the number of hydrogen atoms in one molecule of an acid.

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Exercise

  1. 11.2 g of potassium hydroxide were made up to 1 litre of aqueous solution. 25cm3 of this solution required 24.9cm3 of 0.1 M of an acid HnX. Dertermine the value of n in the acid(i.e the basicity of the acid) (Answer=2)
  2. 1.5g of sodium hydroxide contained in 250cm3 of solution was used to titrate 0.1M hydrochloric acid. What volume of acid would be needed to react with 20cm3 of the alkali? (Answer=30cm3)
  3. 8.50g of a sample of iron required just 75 cm3 of 3.00M hydrochloric acid to dissolve it and give a neutral solution. Calculate the percentage purity of the sample of iron.(Answer=74.1%)
  4. Determine the number of moles of nitrate ions in 1 litre solution,if 6.62g of Lead(II)nitrate are made up to 200cm3 of aqueous solution.(Answer=0.2 moles)
  5. Kyagulanyi and Atim were playing and accidentally poured an acid that was on the table in the drinking water for students. Samanya and Dickens, young analytical chemists titrate the water and find that 10.0dm3 of water are needed to neutralize 10.0cm3 of a 0.010moldm3 solution of sodium hydroxide. What is the concentration of the hydrogen ions in the water.(Answer 0.00005M)
  6. Sodium carbonate crystals (27.823g) were dissolved in water and made up to 1 litre. 25.0 cm3 of the solution were neutralized by 48.8cm3 of hydrochloric acid of concentration 0.10M. Find n in the formula Na2CO3.nH2O.( Answer n=10)

Sample questions on mole concept

  1. 25 cm3 of 0.1M NaOH(aq) required 12.5cm3 of Sulphuric acid solution for complete reaction. Calculate the.
    i) Molarity of the acid
    ii) Concentration of the acid in g/l.
  2. 25cm3 of a solution containing 5.3g/l of a metal carbonate of formula, M2CO3 neutralized 25cm3 of 0.1M Hydrochloric acid. Calculate the
    i) Molarity of the carbonate solution
    ii) Formula mass of the metal carbonate
    iii) Relative atomic mass of the metal (M) in the metal carbonate.
  3. 25cm3 of impure sodium hydroxide solution containing 5.0g of impure sodium hydroxide per litre completely reacted with 20cm3 of 0.1M Hydrochloric acid. Calculate the;
  4. I) molarity of Sodium Hydroxide solution
  5. II) Percentage impurity in the sample of sodium Hydroxide.
  1. 1.00g of a mixture of calcium carbonate was carefully shaken with 200cm3 of distilled water, and then filtered. 20cm3 of the filtrate required 8cm3 of 0.125M Hydrochloric acid for neutralization. Calculate
    i) The mass of Calcium carbonate in the sample
    ii) Percentage purity of sodium carbonate in the mixture
  2. 25cm3 of sodium carbonate required 27.25cm3 of a solution containing 4g of Hydrochloric acid per litre. Calculate the concentration of sodium carbonate in grams per litre of solution.
  3. 25cm3 of a solution containing 12.0g of sodium hydroxide per litre, required 15cm3 of a solution containing 18.25g/l of acid, HA. Calculate the formula mass of the acid.
  4. 20cm3 of 0.12M Potassium hydroxide required 24 cm3 of a solution of a dibasic acid, H2X containing 1.225g per 250cm3 of solution. Calculate the formula mass of the acid.
  5. 32.5cm3 of a solution containing 6.1 g/l of an acid, HXO3, required 25cm3 of a solution containing 5.0g/l of sodium hydroxide solution. Calculate the relative atomic mass of the acid.
  6. 20cm3 of a solution containing 25.8g/l of a dibasic hydrated acid, H2X.nH2O neutralized 10 cm3 of 0.8M sodium Hydroxide solution. If the relative formula mass of H2X = 90, determine the value of n
  7. 20cm3 of nitric acid solution containing 6.3g/l of solution required 25 cm3 of a metal carbonate, M2CO3, solution containing 5.52 g/l of solution for neutralization. Calculate the relative mass of metal M.