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Ammonium sulfate is a fertiliser which is manufactured by the reaction between ammonia and sulfuric acid.
(a) Ammonia is described as a weak base and sulfuric acid as a strong acid.
By using an equation, explain clearly what is meant by the term weak base. [3]
(b) Ammonia and sulfuric acid are both manufactured by processes which involve chemical equilibria.
(i) Sulfuric acid is produced from sulfur trioxide which is made by the Contact process.
State three important operating conditions for the Contact process for the manufacture of sulfur trioxide.
For each of your conditions, you should avoid the use of vague phrases such as 'high temperature'.
condition 1 ..............................................................................................
condition 2 ..............................................................................................
condition 3 .............................................................................................. [2]
(ii) How is the sulfur trioxide produced converted into sulfuric acid? [4]
(c) Chloropropanols such as 1,3-dichloropropan-2-ol (1,3-DCP) are present in some foods.
$$\text{C/CH}_2\text{CH(OH)CH}_2\text{Cl}$$
1,3-DCP
(i) What will be produced when 1,3-DCP is reacted separately with the following reagents under suitable conditions?
In each case give the structural formula.
concentrated sulfuric acid
an excess of ammonia [4]
(ii) Describe as fully as you can what type of reaction occurs with ammonia. [4]
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Chile saltpetre is a mineral found in Chile and Peru, and which mainly consists of sodium nitrate, NaNO_3. The mineral is purified to concentrate the NaNO_3 which is used as a fertiliser and in some fireworks.
In order to find the purity of a sample of sodium nitrate, the compound is heated in NaOH(aq) with Devarda's alloy which contains aluminium. This reduces the sodium nitrate to ammonia which is boiled off and then dissolved in acid.
$3NaNO_3(aq) + 8Al(s) + 5NaOH(aq) + 18H_2O(l) \rightarrow 3NH_3(g) + 8NaAl(OH)_4(aq)$
The ammonia gas produced is dissolved in an excess of $H_2SO_4$ of known concentration.
$2NH_3 + H_2SO_4 \rightarrow (NH_4)_2SO_4$
The amount of unreacted $H_2SO_4$ is then determined by back-titration with NaOH of known concentration.
$H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O$
(a) A 1.64 g sample of impure $NaNO_3$ was reacted with an excess of Devarda's alloy.
The $NH_3$ produced was dissolved in 25.0 $cm^3$ of 1.00 mol $dm^{-3}$ $H_2SO_4$.
When all of the $NH_3$ had dissolved, the resulting solution was titrated with NaOH(aq).
For neutralisation, 16.2 $cm^3$ of 2.00 mol $dm^{-3}$ NaOH were required.
(i) Calculate the amount, in moles, of $H_2SO_4$ present in the 25.0 $cm^3$ of 1.00 mol $dm^{-3}$ $H_2SO_4$.
(ii) Calculate the amount, in moles, of NaOH present in 16.2 $cm^3$ of 2.00 mol $dm^{-3}$ NaOH.
(iii) Use your answer to (ii) to calculate the amount, in moles, of $H_2SO_4$ that reacted with 16.2 $cm^3$ of 2.00 mol $dm^{-3}$ NaOH.
(iv) Use your answers to (i) and (iii) to calculate the amount, in moles, of $H_2SO_4$ that reacted with the $NH_3$.
(v) Use your answer to (iv) to calculate the amount, in moles, of $NH_3$ that reacted with the $H_2SO_4$.
(vi) Use your answer to (v) to calculate the amount, in moles, of $NaNO_3$ that reacted with the Devarda's alloy.
(vii) Hence calculate the mass of $NaNO_3$ that reacted.
(viii) Use your answer to (vii) to calculate the percentage by mass of $NaNO_3$ present in the impure sample.
Write your answer to a suitable number of significant figures.
(b) The above reaction is an example of a redox reaction.
What are the oxidation numbers of nitrogen in $NaNO_3$ and in $NH_3$?
$NaNO_3$ ....................... $NH_3$ .......................
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This question refers to the elements in the section of the Periodic Table shown below.
\[\begin{array}{cccccc} \text{H} & & & & \text{He} \\ \text{Li} & \text{Be} & \text{B} & \text{C} & \text{N} & \text{O} & \text{F} & \text{Ne} \\ \text{Na} & \text{Mg} & \text{Al} & \text{Si} & \text{P} & \text{S} & \text{Cl} & \text{Ar} \\ \text{K} & \text{Ca} & \text{................ transition elements ................} & \text{Ga} & \text{Ge} & \text{As} & \text{Se} & \text{Br} & \text{Kr} \end{array}\]
(a) From this list of elements, identify in each case one element that has the property described. Give the symbol of the element.
(i) An element that when placed in cold water sinks and reacts readily.
..........
(ii) An element whose molecules contain $\pi$ bonding.
..........
(iii) An element that forms a gaseous toxic oxide.
..........
(iv) The element which has a giant molecular structure and forms an oxide which also has a giant molecular structure.
..........
(v) An element that forms a covalent chloride which dissolves in water to give a conducting solution.
..........
(vi) The element in Period 3 (Na to Ar) with the greatest electrical conductivity.
..........
(b) Some of the elements in Period 3 (Na to Ar) burn with a coloured flame when heated in oxygen or chlorine.
(i) Give the symbol of one such element, the formula of the oxide formed, and state the flame colour that would be seen.
symbol of element .............................................
formula of oxide ...............................................
flame colour .....................................................
(ii) For the element you have used in (i), give the formula of the chloride formed, and state the pH of the solution produced when this chloride is shaken with water.
formula of chloride ...............................................
pH of solution ......................................................
(c) Chlorine reacts with both bromine and iodine to form \text{BrCl} and \text{ICl} respectively. The melting points of chlorine and the two chlorides are shown in the table.
\[\begin{array}{|c|c|c|c|} \hline \text{substance} & \text{Cl}_2 & \text{BrCl} & \text{ICl} \\ \hline \text{m.p. /}^{\circ}\text{C} & -101 & -66 & 24 \\ \hline \end{array}\]
(i) Showing outer electrons only draw a 'dot-and-cross' diagram of the bonding in \text{ICl}.
(ii) Suggest why the melting points increase from \text{Cl}_2 to \text{ICl}.
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..................................................................................
(iii) Suggest which of these three molecules has the largest permanent dipole. Explain your answer.
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(a) In the boxes below, write the structural formula of the organic compound formed when crotyl alcohol is reacted separately with each reagent under suitable conditions. If you think no reaction occurs, write 'NO REACTION' in the box.
[Table_1]
A. $\text{Br}_2$ in an inert organic solvent
B. $\text{PCl}_5$
C. $\text{H}_2$ and Ni catalyst
D. $\text{NaBH}_4$
E. $\text{K}_2\text{Cr}_2\text{O}_7$/ $\text{H}^+$ heat under reflux
[5]
(b) Draw the displayed formula of the organic compound formed when crotyl alcohol is reacted with cold, dilute acidified potassium manganate(VII).
[1]
(c) Draw the skeletal formula of the compound formed in reaction E.
[2]
(d) Crotyl alcohol is obtained from crotonaldehyde, $\text{CH}_3\text{CH=CHCHO}$.
(i) Describe one test that would confirm the presence of a small amount of unreacted crotonaldehyde in the crotyl alcohol. Give the name of the reagent used and state what you would see.
reagent .......................................................
observation ...................................................
(ii) What type of reaction is the conversion of crotonaldehyde into crotyl alcohol?
.................................................................. ..................
[3]
(e) Compound P, another unsaturated compound, is found in some blue cheeses. The percentage composition by mass of compound P is C: 73.7%; H: 12.3%; O: 14.0%. Calculate the empirical formula of compound P.
[2]
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A student reacted together an alcohol and a carboxylic acid under appropriate conditions to produce an ester. A sweet smelling organic liquid, Q, with the empirical formula $C_2H_4O$ was produced. The $M_r$ of Q was found by experiment to be 87.5.
(a) What is the molecular formula of Q?
............................................................................................................................................................... [1]
(b) In the boxes below, draw the structural formulae of four isomers with this formula that are esters.
[4]
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