Analía Bellizzi – Chemistry Classes

Ronald Reagan High School

AS Amount of Substance # 6 More complex calculations

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1.2 Exercise 6 – more complex calculations

  1. 1. Succinic acid has the formula (CH 2 ) n (COOH) 2 and reacts with dilute sodium
    hydroxide as follows: (CH 2 ) n (COOH) 2 + 2NaOH ==> (CH 2 ) n (COONa) 2 + 2H 2 O
    2.0 g of succinic acid were dissolved in water and the solution made up to 250
    cm 3 . This solution was placed in a burette and 18.4 cm 3 was required to neutralise
    25 cm 3 of 0.1 moldm -3 NaOH. Deduce the molecular formula of the acid and
    hence the value of n.
  2. Sodium carbonate exists in hydrated form, Na 2 CO 3 .xH 2 O, in the solid state. 3.5 g
    of a sodium carbonate sample was dissolved in water and the volume made up to
    250 cm 3 . 25.0 cm 3 of this solution was titrated against 0.1 moldm -3 HCl and 24.5
    cm 3 of the acid were required. Calculate the value of x given the equation:
    Na 2 CO 3 + 2HCl ==> 2NaCl + CO 2 + H 2 O
  3.  25 cm 3 of a sample of vinegar (CH 3 COOH) was pipetted into a volumetric flask
    and the volume was made up to 250 cm 3 . This solution was placed in a burette and
    13.9 cm 3 were required to neutralise 25 cm 3 of 0.1 moldm -3 NaOH. Calculate the
    molarity of the original vinegar solution and its concentration in gdm -3 , given that
    it reacts with NaOH in a 1:1 ratio.
  4.  2.5 g of a sample of impure ethanedioic acid, H 2 C 2 O 4 .2H 2 O, was dissolved in
    water and the solution made up to 250 cm 3 . This solution was placed in a burette
    and 21.3 cm 3 were required to neutralise 25 cm 3 of 0.1 moldm -3 NaOH. Given that
    ethanedioic acid reacts with NaOH in a 1:2 ratio, calculate the percentage purity
    of the sample.
  5.  A toilet cleaner containing sodium hydrogensulphate, NaHSO 4 is believed to have
    been contaminated. 5.678 g of the sample were dissolved in water and the
    solution was made up to 250 cm 3 . This solution was placed in a burette and 23.1
    cm 3 of it were required to neutralise 25 cm 3 of 0.1 moldm -3 sodium hydroxide.
    Calculate the percentage purity of the sample given that the species react in a 1:1
    ratio.
  6. . When silicon tetrachloride is added to water, the following reaction occurs:SiCl 4 (l) + 2H 2 O(l) ==>SiO 2 (s) + 4HCl(aq)1.2 g of impure silicon tetrachloride was dissolved in excess water, and theresulting solution was made up to 250 cm 3 . A 25 cm 3 portion of the solution wasthen titrated against 0.10 moldm -3 sodium hydroxide, and 18.7 cm 3 of the alkaliwere required. What was the percentage purity of the silicon tetrachloride?
  7.  13.2 g of a sample of zinc sulphate, ZnSO 4 .xH 2 O, was strongly heated until no further change in mass was recorded. On heating, all the water of crystallisation evaporated as follows: ZnSO 4 .xH 2 O ==> ZnSO 4 + xH 2 O.Calculate the number of moles of water of crystallisation in the zinc sulphatesample given that 7.4 g of solid remained after strong heating.