HKDSE Chemistry selected questions for revision
Karson Li
Exercise 1 / date: 27 Sept 2023
MCQs
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Long Questions
1.
Gas X with irritating pungent smell is produced in a chemical reaction. A student attempted to collect X by the
following method but failed.
Later on, he found out a red litmus paper turns blue with the water after the collection trial.
a. Suggest what X is. Why the collection method failed? (2)
b. Draw a labelled diagram to suggest how X could be effectively collected. (3)
c. Explain, in terms of chemical equation, why litmus paper turns blue in the case. (3)
2.
State methods, including chemical used, to distinguish the following species. State the observable changes. If
chemical test(s) is used, write the equation. (More than 1 chemical could be used in some pairs.)
a. PbNO3(aq), Zn(NO3)2(aq)
b. Na2CO3 (s), Na2SO3 (s)
c. Benzoic acid, Phenol
,
d. Equal volume of 0.5M NH3(aq), and 0.5M NaOH(aq)
(8)
3.
Following is the structure of a dibasic acid with chemical formula H2C2O4.
a.
Give systematic name of this acid. (1)
b. A student expected 0.500 mol dm-3 standard H2C2O4(aq) to have a pH of 1.0. However when measured with
calibrated pH meter, it was fount to be greater than 1.
Explain this observation with the aid of a chemical equation. (2)
c.
Explain why standard NaOH(aq) cannot be directly prepared by weighing NaOH(s) and dissolving in water. (1)
d. In a titration experiment, 25.00 cm3 of 0.0500 mol dm-3 standard H2C2O2(aq) and a few drops of phenophelein
indicator were placed in a conical flask. NaOH(aq) of unknown concentration was added from burette into the flask.
17.20cm3 of NaOH(aq) was required to reach the end point.
(i) state the color change at end point (1)
(ii) Calculate the concentration of NaOH(aq) in mol dm-3.
4.
Fill in the table. Draw detailed diagrams, showing electrons and include types of special bondings if necessary.
3D- structure diagram
Name of shape of ion/molecule
Polarity (yes,
no)
Ammonium ion
Ammonia
Ethene
Phosphorus pentachloride
Sulphur hexafluoride
Nitrogen trifluoride
Sulphur dioxide
5.
An experiement using three metals, X, Y ,Z, with results shown.
Tick (√) means reaction occurs, cross( x) means no reaction, while (?) means the experiment result is unknown.
↓Reactions / Metal→
X (s)
Y (s)
Z (s)
0.2M H2SO4(aq)
×
√
×
0.2M HNO3(aq)
×
√
√
Reaction of metal oxide
?
?
√
?
√
?
with carbon (s)
Reaction with cold water
a. Suggest what Z(s) is. (1)
b. Arrange reactivity of X,Y and Z in ascending order. (1)
b. Write the chemical equation of oxide of Z with carbon. Name the reaction type. (2)
c. It is known that Y forms a salt with cyanide, CN-(aq) ions, in a molecular formular of Y(CN)2. Suggest what Y is, and
state color of Y ions in a flame test. (2)
6.
Consider the following reaction.
At room temperature and pressure, a micro-scaled experiment is performed. 0.08g of methyl oleate in organic solvent
is allowed to react with excessive H2(g). H2(g) flowed from inverted measuring cylinder to reacting flask through the
tubing.
a.
Suggest 1 advantage of performing this reaction in micro-scaled experiments. (1)
b. Explain why the right end of tubing is placed in the uppermost position of inverted measuring cylinder.
(1)
c. Suggest 1 observable change in the inverted measuring cylinder in experiment during the reaction . (1)
d. Calculate theoretical volume of H2(g) needed to complete the reaction at room temperature and pressure.
(Molar volume of gas at standard temperature, pressure =
Relative molecular mass of methyl oleate = 296.0 g)
24dm3
(3)
e. Sketch in the graph below the variation of the volume of H2(g) in the measuring cylinder, with time from start until
completion of reaction. (Measuring cylinder initially contains 10.0cm3 of H2(g). The first few points have been given to
facilitate the sketch. ) Label this sketch as A. (2)
d. Give another sketch and label with ‘B’ as required in © but only using 0.040g of methyl oleate for the reaction while the
other conditions remain unchanged. (1)
7.
The following reaction is kept in a vessel with constant pressure at 500K. Suppose the equilibrium constant at
standard temperature and pressure is Kc1.
Suppose platinum (Pt) is a catalyst for the reaction.
A(g) + B(g)
⇌
C(g) + 2D(g)
ΔH=−10.4kJ/mol
…… Kc1
(absence of Pt)
State the change in new equilibrium constant, Kc2, when following action is done on system. (5)
Change in Kc2
Rate of forward
Rate of backward
Equilibrium position
reaction
reaction
shift
(left, right,
unchanged)
Inject Ar(g) in
system
Adding C(g) in
system
↑ Temperature to
700K
Adding Pt in system
↓ volume of vessel
8.
Following shows citric acid, a tribasic organic acid present in lemon, which is a white solid in room temperature.
（Molar mass = 192.0 g）
a. Circle all ionizable hydrogen atom(s) making it an acid. (1)
b. Determine if it is a strong or weak acid, and define the term strong acid. (2)
c. State 2 functional groups in citric acid. (1)
d. A solid sample contains citric acid with other soluble, inert impurities. 1.65g of sample was dissolved in deionized
water, diluted to 250cm3 in apparatus X. Later on, 25cm3 of diluted solution is withdrawn, titrated with 0.123 M
NaOH(aq). 18.45 cm3 of NaOH (aq) was required to reach the end point.
(i) State apparatus X (1)
(ii) Calculate percentage by mass of citric acid in the solid sample. Show your steps. (4)
9.
Consider the following organic reactions:
a.
Write the structural formula of C. (1)
b. Deduce the structural formula of B. (1)
c.
Name the type of reaction of conversion of B to C. (1)
d. Deduce structural formula of A and draw its 3-D structure. Label this formula all chiral centre(s) with *, and draw its
enantiomer. (2)
e. State reagent(S) and condition required for converting A to B,. (1)
10. Ethyne is a gaseous hydrocarbon with molecular formula C2H2.
a. Suggest why enthalpy change of formation of C2H2(g) cannot be determined directly by experiment. (1)
b. Hess’s law can be used to find enthalpy change which cannot be determined directly from experiment. State hesses
law. (1)
c. State standard conditions for ‘standard enthalpy change’. (1)
c. The standard enthalpy change of combustion △Hc of C2H2(g), C(graphite), H2(g) are given below:
With help of correct enthalpy change cycle (draw with labels), calculate enthalpy change of formation of C2H2(g).
11. Explain the following base on chemistry principles you learnt.
a. Melting point of CS2 is higher than that of CO2. (2)
b. Galvanizing provides better corrosion protection than tin-plating in effectiveness. (2)
c. Concentrated nitric acid turns brown in transparent bottle. (2)
d. HF has a higher boiling point than HBr. (2)
e. Red wine turns more sourish under years. (2)
f. Propanediol is more soluble than propanol in water. (2)
g. CO2 and SO2 is acidic gases.
(with chemical equations) (3)
12. Sturctures of some organic compounds are shown below.
a.
Identify the tertiary alcohol compound (give the letter.) (1)
b. Label all chiral centre(s), if any, on the structure of W below. (1)
c.
Heating X under reflux in 2M NaOH(aq) can form an optically active organic compound U and an optically inactive
compound V. Draw and structure of U and V. (2)
d. Consider the following reagents:
Br2(aq),
K2Cr2O4/H+ (aq),
Na2CO3(aq)
Suggest which one of the above reagents can be used to perform chemical test to distinguish X from W,Y and Z.
State the observation in the test and explain your answer. (2)
11. Propanoic acid reacts with cyclohexanol to form an organic compound Q.
a. Write the chemical formula of the reaction, with conditions needed. (2)
b. Name compound Q. State which functional group is Q, and Give a common property of this homologous family. (3)
c. Draw an experiment setup for preparing ester from propanoic acid and cyclohexanol. (with title, correct apparatus
and labels).
e.
(3)
When reacting with concentrated NaOH(aq), Q decomposed to form two main products.
(i) Write the chemical formula of the reaction.
(ii) Name this specific type of reaction. (1)
(2)