1. Ethanedioic acid is a diprotic acid. A student determined the value of x in the formula of hydrated ethanedioic acid, HOOC−COOH•xH2O, by titrating a known mass of the acid with a 0.100 mol dm−3 solution of NaOH (aq).
0.795 g of ethanedioic acid was dissolved in distilled water and made up to a total volume of 250 cm3 in a volumetric flask.
25 cm3 of this ethanedioic acid solution was pipetted into a flask and titrated against aqueous sodium hydroxide using phenolphthalein as an indicator.
The titration was then repeated twice to obtain the results below.
(a) State the uncertainty of the volume of NaOH added in cm3.
(b) Calculate the average volume of NaOH added, in cm3, in titrations 2 and 3, and then calculate the amount, in mol, of NaOH added.
(c) (i) The equation for the reaction taking place in the titration is:
HOOC−COOH (aq) + 2NaOH (aq) → NaOOC−COONa (aq) + 2H2O (l)
Determine the amount, in mol, of ethanedioic acid that reacts with the average volume of NaOH (aq).
(ii) Determine the amount, in mol, of ethanedioic acid present in 250 cm3 of the original solution. (iii) Determine the molar mass of hydrated ethanedioic acid.
(iv) Determine the value of x in the formula HOOC−COOH•xH2O.
(d) Identify the strongest intermolecular force in solid ethanedioic acid.
(e) Deduce the Lewis (electron dot) structure of ethanedioic acid, HOOC−COOH.
2. Bromomethane was used as a pesticide until it was found to be ozone-depleting.
(a) State the equation for the reaction between methane and bromine to form bromomethane.
(b) Explain, using equations, the complete free-radical mechanism for the reaction of methane with bromine, including necessary reaction conditions.
(c) Bromine can be produced by the electrolysis of molten sodium bromide. Deduce the half-equation for the reaction at each electrode.
Positive electrode (anode):
Negative electrode (cathode):
(d) Bromine reacts with aqueous sodium iodide:
Br2 (aq) + 2NaI (aq) → I2 (aq) + 2NaBr (aq)
Identify the oxidizing agent in this reaction.
3. The rate of reaction is an important factor in industrial processes such as the Contact process to make sulfur trioxide, SO3 (g).
2SO2 (g) + O2 (g) ⇔2SO3 (g) ΔHθ = −198 kJ
(a) Define the term rate of reaction。
(b) Describe the collision theory.
4. (a) State the relative mass and charge of the subatomic particles of an atom.
(b) (i) Calculate the number of neutrons and electrons in one atom of 65Cu.
(ii) State one difference in the physical properties of the isotopes 63Cu and 65Cu and explain why their chemical properties are the same.
(c) Describe the bonding in solid copper.
(d) Suggest two properties of copper that make it useful and economically important.