Question 3
QUESTION 3
(a) Consider the following structure of an organic compound.
(i) Draw the structures of two of the isomers of the compound;
(ii) State the IUPAC name of each of the isomers drawn in 3(a)(i);
(iii) Mention the homologous series to which each of the isomers drawn in 3(a)(i) belongs;
(iv) write a balanced chemical equation for the combustion of the compound;
(v) Describe briefly a chemical test for each of the products formed in the reaction stated in 3(a)(iv).
(b) The following figure illustrates a section of the periodic table. Use the figure to answer the questions that follow.
(i) What letter represents the most:
I. reactive metal?
II. reactive non-metal?
III. electronegative element?
(ii) Write the electron configuration of Y. [5 marks]
(c) Decomposition of MgCO3 produced 78 cm3 of CO2 at 27 º C and 200 kPa according to the following reaction equation: MgCO3(s) MgO(s) + CO2(g )
Calculate the mass of CO2 produces. [Molar mass of CO2 = 44.0, R =8.31 kPa dm3 K-1 mol-1] [6 marks]
(d) State one laboratory use of each of the following compounds:
(i) KMnO4;
(ii) MnO2. [2 marks]
Observation
This question was popular among the candidates, and their performance was above average.
In part (a), majority of the candidates were able to draw the structures of two of the isomers of the compound.
In addition to this, they were able to state the IUPAC name of each of the isomers drawn.
In part (b), majority of the candidates were able to locate in the periodic table, the letters that represented the
reactive metal, reactive non-metal and electronegative element.
In part (c), majority of the candidates could not calculate the mass of CO2 produced from decomposition of MgCO3.
In part (d), majority of the candidate were able to state the laboratory use of KMnO4 and MnO2.
(2 marks)
(ii) 2-methylpropene
trans- but -2- ene
but -1- ene
cyclobutane
methylcyclopropane
(iii) alkenes
cycloalkanes
(iv) C4H8 + 6O2 → 4CO2 + 4H2O
(v) Bubble CO2 through lime water the lime water turns milky
Add water to white anhydrous CuSO4 it turns blue OR Add water to blue anhydrous cobalt (II) chloride it turns pink
(b) (i) I. Y
II. P
III. P
(ii) 1s2 2s2 2p6 3s23p6 4s1
(c) T = 27 + 273 = 300 K
n = PV
RT
= 200 x 0.078
8.31 x 300
= 6.26 x 10-3
Mass of CO2 = 6.26 x 10-3 x 44
= 0.275 g
ALTERNATIVE METHOD
T = 27 + 273 = 300 K
M = MRT/PV
m =MPV/RT
=44.0 x 200 x 0.078
8.31x 300
m = 0.275g
(d) (i) KMnO4 - used as an oxidizing agent
used to test for unsaturation in organic compounds
(ii) MnO2 - used as a catalyst
used as an oxidizing agent