(a)(i) Draw the energy profile diagram for the reaction
H\(_{2(g)}\) + I\(_{2(g)}\) —> 2HI\(_{(g)}\) \(\Delta\) = —13 kJmol\(^3\)
(ii) If the concentration of HI increases from 0 to 0.001 mol dm\(^3}\) in 50 seconds, what is the rate of the reaction?
(b) State the type of salt represented by each of the following compounds:
(i) K\(_4\)Fe(CN)\(_6\) (ii) (NH\(_4\))\(_2\)Fe(SO\(_4\))\(_2\)6H\(_2\)O (iii) Mg(OH)NO\(_3\) (iv) NaH\(_2\)PO\(_4\).
(c) Explain, giving equations, the following observation: When carbon (IV) oxide is passed into lime water, it turns milky initially but turns clear with excess carbon (IV) oxide.
(d)(i) Give one use for each of the following compounds: CaCO\(_3\), CaSO\(_4\), NaHCO\(_3\).
(ii) State a drying agent for each of the following gases: i. NH\(_3\), II. HCI Ill. SO\(_4\).
(iii) Write an equation to illustrate the reaction of ammonia as a reducing agent.
(e) An industrial raw material has the following composition by mass:
Iron = 28.1%
Chlorine = 35.7%
Water of crystallization = 36.2%
Calculate the formula for the material. [ H = 1, 0 = 16, Cl = 35.5, Fe = 56 ].
Explanation
(ii) Change in concentration of HI = 0.001 – 0.00
= 0.001 mol/dm\(^3\)
Time of reaction = 50 sec.
Rate of reaction = \(\frac{0.001}{50}\) = 2 x 10\(^-5\) mol/dm\(^3\)/s\(^1\)
(b)(i) K\(_4\)Fe(CN)\(_6\) — Complex salt
(ii) (NH\(_4\))\(_2\)Fe(SO\(_4\))\(_2\).6H\(_2\)O — Double salt
(iii) Mg(OH)NO\(_3\) Basic salt
(iv) NaH\(_2\)PO\(_4\) — Acid salt
(c) When carbon (IV) oxide is passed into lime water, it turns milky or cloudy due to the formation of insoluble calcium trioxocarbonate (IV).
Ca(OH)\(_{2(aq)}\) + CO\(_{2(g)}\) \(\to\) CaCO\(_{3(s)}\) + H\(_2\)O\(_{(l)}\)
On passing more or excess CO\(_2\) the soluble calcium hydrogen trioxocarbonate (IV) is formed.
CaCO\(_3\) + H\(_2\)O + CO\(_2\) \(\to\) Ca(HCO\(_3\))\(_{(aq)}\)
(d)(i) CaCO\(_3\) — extraction of iron, cement manufacture, manufacture of CaO and lime water [Ca(OH)\(_2\) ].
CaSO\(_4\) — for cast as Plaster of Paris
NaHCO\(_3\) — for baking, antacids, acid-base titrations, detection of acid, function in organic compounds.
(ii) NH\(_{3(g)}\) — Calcium oxide (CaO).
HCl — concentrated (H\(_2\)SO\(_4\)).
SO\(_2\) — concentrated H\(_2\)SO\(_4\)
(iii) 2NH\(_{3(g)}\) + 3CuO\(_{(s)}\) \(\to\) 3Cu\(_{(s)}\) + 3H\(_{2}\)O\(_{(l)}\) + N\(_{2(g)}\)
(e) Fe Cl H\(_2\)O
No. of moles 28.1 35.7 36.2
56 35.5 18
Divide by smallest 0.5 2 2
0.5 0.5 0.5
1 : 2 : 4
FeCl\(_2\).4H\(_2\)O