basic concepts in chemistry

1. CHEMISTRY
FORM 4 – PREPARATION FOR STANDARDIZED TEST
1) An experiment is conducted to investigate the effect of temperature on the rate of reaction. 5
set of 50cm3 of 1.0 mol dm-3 sulphuric acid is reacted with 5g of magnesium ribbon at a
different temperature.
a) State a problem statement for above experiment. [2 m ]
______________________________________________________________
b) Identify all the variables in this experiment. [3m]
i) Manipulated variable :______________________________________
ii) Responding variable : ______________________________________
iii) Controlled variable : ______________________________________
c) State one suitable hypothesis for this experiment. [2 m ]
___________________________________________________________
2) A group of students has carried out an experiment to determine the melting point of substance
Y. A boiling tube contained substance Y solid is heated in a water bath. The temperature of
substance Y is recorded every 30 seconds. The result is as shown in table 2 below.
Time 0 ½ 1 1½ 2 2½ 3 3½ 4 4½
(min)
Temperature 60.0 64.0 68.0 72.0 76.0 80.0 80.0 80.0 80.0 80.0
(o C)
Time 5 5½ 6 6½ 7 7½
(min)
Temperature 80.0 80.0 80.0 83.0 86.0 89.0
(o C)
Table 2
(a) Draw a graph of the temperature against time for the experiment and locate the melting
point for substance Y [4 m]
(b) Explain why there is no change in temperature from min 2½ to 6 min.[2m]
1

2. __________________________________________________________
(c) Draw the arrangement of particles at 2 minutes of heating. [1m]
3. Table 3 shows the proton number and nucleon number for atom
V, W, X, Y and Z.
Atom Proton number Nucleon
number
V 1 1
W 1 2
X 3 7
Y 6 12
Z 20 40
Table 3
Based on information given in Table 3, answer the following questions.
a) What is meant by nucleon number? [1 m]
_________________________________________________________
b) What is the number of neutron for particle W ? [1 m]
_________________________________________________________
c) Write the electron arrangement for atom [1 m]
V : _____________________
Z : _____________________
d) Draw the structure of atom X [1 m]
e) Which of the above atoms are isotopes? Explain your answer. [2 m]
2

3. ____________________________________________________________
f) How many valence electrons in atom X? [1 m]
___________________________________________________________
4. An experiment was conducted in order to determine the empirical formula of magnesium
oxide.
a) Give the meaning of empirical formula. [1 m]
___________________________________________________________
b) Why must the magnesium ribbon be cleaned with sandpaper? [1 m]
___________________________________________________________
c) Why the crucible need to be covered with its lid as soon as the magnesium start burning?
[1 m]
___________________________________________________________
d) The results of the experiment are as follows:
Description Mass, g
Mass of crucible + lid 22.30
Mass of crucible + lid + magnesium 24.70
Mass of crucible + lid + magnesium oxide 26.30
[relative atomic mass: O,16 ; Mg,24]
Based on the above result,
i) Calculate the mass of magnesium used. [1 m]
ii) Calculate the mass of oxygen that reacts with magnesium. [1 m]
iii) Calculate the number of moles of magnesium used. [1 m]
iv) Calculate the number of moles of oxygen that has reacted. [1 m]
v) Determine the empirical formula of magnesium oxide. [1 m]
5. The reaction between hydrochloric acid and zinc carbonate was written below.
3

4. hydrochloric acid + zinc carbonate → zinc chloride + carbon dioxide + water
a. Write the chemical formula for zinc chloride. [1 m]
____________________________________________________
b. Rewrite the equation above as chemical equation. [2 m]
____________________________________________________
c. If 12.5 g of zinc carbonate react completely in the reaction above
calculate,
[given molar mass calcium carbonate = 125 g/mol, relative atomic mass: Zn,65;
C,12;O,16;H,1;Cl,35.5; molar volume of gas at room temperature: 24dm3/mol]
i) the number of mole of hydrochloric acid being used? [3m]
ii) the mass of zinc chloride obtained. [2m]
iii) the volume of gas collected at room temperature. [2m]
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