CSEC Chemistry Paper 2 May/June 2008 - Free CXC Past Paper with Answers

Identify the group in the periodic table in which fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At) are placed. Give ONE reason for your answer.

Group: Reason:

Figure 3 represents the experimental set up used by a group of students who are investigating the reactivity of halogens.

What would the students observe when they conduct the experiment represented in Figure 3? Illustrate your answer by means of an equation.

Figure 3. Experiment to investigate the reactivity of halogens

Two compounds of Elements X and Y undergo the reactions recorded in Table 3. Study the information carefully and answer the questions that follow.

TABLE 3: REACTIONS OF COMPOUNDS OF ELEMENTS X AND Y

Deduce whether X and Y are metals or nonmetals.

X is _________________________________________________________________________ Y is _________________________________________________________________________

Based on your answer to (c) (i) above, describe the bonding in Element Y.

Predict the type of bond that would be formed between X and oxygen. Give a reason for your answer.

Type of bonding: _________________________________________________________________ Reason: _________________________________________________________________________

Based on the information given in Table 3, arrange the elements Mg, X and Y in order of decreasing activity. Explain your answer.

Order of activity (most reactive first): ___________________________________________ Explanation: ____________________________________________________________________

Complete Table 4 by a) identifying the reagents b) drawing the fully displayed structures of the products.

TABLE 4: REACTIONS OF ETHANOL

Define 'structural isomerism'.

Draw fully displayed structures of but-1-ene and but-2-ene.

But-1-ene But-2-ene

Draw and name ONE OTHER structural isomer of $C_4H_8$.

State ONE physical property of $C_4H_8$.

Ethanol will react under different conditions to produce compounds with the following functional groups:

$\text{C = C}$ $\text{O}$ $\text{||}$ $\text{- C - OH}$ $\text{O}$ $\text{||}$

What is meant by a 'functional group'?

Ethanol reacts with different reagents to form products with the functional groups shown in Table 4.

Complete Table 4 by a) identifying the reagents b) drawing the fully displayed structures of the products.

TABLE 4: REACTIONS OF ETHANOL

Barium (Ba) is below calcium in the same group in the periodic table.

Draw a fully labelled diagram of the apparatus which could be used in the electrolysis of molten $BaBr_2$. You should indicate the material from which the electrodes are made.

Write equations to indicate the chemical reactions which occur at the electrodes.

A current of 5A is passed for 2 minutes through the molten $BaBr_2$. Calculate the mass of the product that will be formed at the cathode.

(Relative atomic mass: Ba = 137, Br = 80) (1 Faraday = 96 500 C $mol^{-1}$)

List TWO factors which can in general affect the products formed during electrolysis of compounds.

State ONE reason why the reaction of barium with water is faster than the reaction of calcium with water.

From the compounds A to D above, select ONE compound which is saturated and ONE compound which is unsaturated.

From the compounds A to D above, select ONE compound which is saturated and ONE compound which is unsaturated.

Name AND give the general formula for the homologous series to which EACH of the two compounds selected in (a) (i) above belongs.

Nitrogen constitutes about 78% of the gases in the atmosphere. It exists as very stable diatomic molecules. It undergoes very few but important reactions (called fixation reactions) to produce nitrogenous compounds required by plants.

Nitrogen is "fixed" by the Haber process according to the following equation:

$N_2 + 3H_2 \rightleftharpoons 2NH_3$

With reference to the nitrogen cycle:

Name ONE process by which nitrogen in the atmosphere can be converted into nitrates.

Name ONE process by which nitrogen in the nitrates in soil is released back into the atmosphere.

Two metal nitrates, P and Q, are separately heated. P gives off a colourless gas which rekindles a glowing splint. Q gives off a brown gas.

Which of these two metal nitrates, P or Q, possibly contains

• Group 1 metal?
• Group 2 metal?

Write a chemical equation to show the reaction taking place when Q is heated.

When silica is mixed with sodium carbonate and calcium carbonate and heated strongly, the mixture forms a transparent liquid which, when cooled, becomes glass. Different types of glass can be produced by varying the proportions of these reactants and by adding other substances.

State TWO benefits of adding sodium carbonate or calcium carbonate to silica in the manufacture of glass.

State how the basic components of glass are modified to produce

• lead-potassium glass
• borosilicate glass.

Glass is a non-crystalline solid which melts over a wide range of temperatures. It consists mainly of silicates ($SiO_x$). The chemical bonds in the $SiO_x$ tetrahedron are not all of the same strength.

Why is it important that glass does NOT crystallize as it cools?

Suggest how the bonding in $SiO_x$ affects what happens when glass melts. Explain why this is important for blowing and moulding glass.

Although no scarce and vital raw material is used in the manufacture of glass, recycling of glass is strongly recommended. Suggest TWO reasons for this.

Glass is now widely used as a construction material in buildings. State ONE advantage and ONE disadvantage of using glass in this way.

State the importance of EACH of the following factors in plant growth:

Mineral balance

pH

Humus content of the soil

A farmer observes that the leaves of his bean crop are few in number and yellow in colour. The Agricultural Extension Officer decides to test the farmer's soil for ammonium and iron (III) ions, as well as for its pH.

Briefly describe the test for the presence of ammonium ions in a soil sample.

The Officer finds the soil to be acidic and recommends the addition of lime.

• Suggest ONE possible reason for the acidic nature of the soil.
• Explain the effect of adding lime to the soil. Use a suitable equation to support your answer.

In addition to adding the recommended lime to the soil, also decides to add an ammonium fertilizer, thinking that it would increase his crop yield.

Do you think that the farmer's decision to add both lime and ammonium fertilizer to the soil at the same time is a wise one? Give ONE reason for your answer. Include any relevant chemical equation.