minsung kim 2021-09-13
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I. MULTIPLE
CHOICE: Tick the box of the letter of your correct choice.
1. What is the molar mass, in gmol−1, of a compound if 0.200mol of the compound has a
mass of 13.2g?
a. 66.0
b. 66
c. 26.4
d. 26
Correct answer.
0/1p
Molar Mass = mass/mole = 13.2 g/0.200 mol = 66.0 g/mol = 66.0 gmol-1
Note: 13.2 = 3 sf, 0.200 = 3 sf
Rule: When dividing or multiplying numbers, the number of sf should equal to the least sf of the
two numbers
2. What is the number of carbon atoms in 12g of ethanoic acid CH3COOH, Molar
Mass=60?
a. 0.20
b. 2.0
c. 1.2×10^23
d. 2.4×10^23
Correct answer.
1/1p
Moles ethanoic acid = 12 g / 60 g/mol = 0.20 mol
Note: 1 molecule of CH3COOH = 2 molecules of C  1 mole CH3COOH = 2 mol CH3COOH
Moles of Carbon = (0.20 mol ethanoic acid) x 2 mol C/1 mol ethanoic acid = 0.40 mol C
Number C atoms = 0.40 mol x 6.022 x 1023 = 2.4088 x 1023 = 2.4 x 1023
3. Which is correct?
a. Mixtures are either homogeneous or heterogeneous and their chemical
properties are an average of the individual component properties.
b. Mixtures are never heterogeneous and their chemical properties are
an average of the individual component properties.
c. Mixtures are either homogeneous or heterogeneous and the components retain
their individual chemical properties.
d. Mixtures are never homogeneous and the components retain their individual
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chemical properties.
Correct answer.
Answer: C because mixtures can be either homo or heterogeneous but without changing the
chemical properties of the individual components
Mixture = Asol + Bliq + Cliq (heterogeneous)
Mixture = Dliq + Fliq (Homogeneous)
0/1p
4. What is the sum of the coefficients when the equation is balanced with whole numbers?
1 MnO2 (s) + 4 HCl (aq) → 1 MnCl2 (aq) + 2 H2O (l) + 1 Cl2 (g)
a. 6
b. 7
c. 8
d. 9
Sum of coefficients = 1 + 4 + 1 + 2 + 1 = 9
5. Which formula is correct?
a. NH4PO4
b. (NH4)2PO4
c. (NH4)3PO4
d. (NH4)3(PO4)2
Correct answer.
NH41+
Ammonium
Cation (positively charged ion)
1/1p
PO43Phosphate
Anion (negatively charged ion)
+
The -3 becomes the coefficient of NH4 and +1 becomes the coefficient of PO4
(NH4)3(PO4)1 = (NH4)3PO4
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Example: Aluminum Sulfate
Al3+ + SO42- 
Al2(SO4)3
6. Which diagram represents a heterogeneous mixture?
A.
B.
C.
D.
Heterogeneous Mixture = have at least 2 different components AND at least 2 different phases
(solid, liquid, gas)
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Example: liquid water with ice = 1 component, 2 phases (liquid and solid) = heterogeneous
Example: liquid water = 1 component, 1 phase = homogenous
7. Which is not true about sublimation?
I. It
is an Endothermic process
II. A new product is formed
III. Kinetic energy of particles is increasing
a. I only
b. II only
c. I and III only
d. I, II and III
Example. Dry Ice (solid carbon dioxide)  gas (carbon dioxide) (sublimation)
Sublimation is a physical change, no new product is formed
8. The deposition of gaseous water particles can be represented by which equation?
a. H2O(l) ---> H2O(s)
b. H2O(l) ---> H2O(g)
c. H2O(g) ---> H2O(s)
d. H2O(s) ---> H2O(s)
Deposition
= opposite of sublimation
= gas to solid, physical change
9. Which contains the greatest number of moles of oxygen atoms?
a. 0.05 mol Mg(NO3)2
b. 0.05 mol C6H4(NO2)2
c. 0.1 mol H2O
d. 0.1 mol NO2
0.05 x 6 = 0.3 mol O (answer)
0.05 x 4 = 0.2 mol O
0.1 x 1 = 0.1 mol O
0.1 x 2 = 0.2 mol O
10. What is the sum of the integer coefficients when propene undergoes complete
combustion?
2 C3H6 (g) + 9 O2 (g) → 6 CO2 (g) + 6 H2O (l)
Hydrocarbon
Oxygen (combustion Reaction)
a. 11
b. 17
c. 21
d. 23
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Correct answer.
2C3H6 + 9O2 → 6CO2 + 6H2O
Sum of coefficients = 2 + 9 + 6 + 6 = 23
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11. Which changes of state are exothermic processes?
I. condensation
II. freezing
III. deposition
a. I and II only
b. II and III only
c. I and III only
d. I, II, and III
12. What is the formula of magnesium nitride?
a. MgN
b. Mg2N3
c. Mg3N
d. Mg3N2
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From the table above, Magnesium is Mg2+ and Nitride is N3Mg2+ + N3-  Mg3N2
13. Which is not a pure substance?
a. NaCl(aq)
aq = aqueous (mixed with water)
b. H2O(l)
c. C4H10(l)
d. Cl2(g)
14. What is the sum of the coefficients when the following equation is balanced using the
smallest whole numbers?
1 C6H12O6 (aq) → 2 C2H5OH (aq) + 2 CO2 (g)
a. 4
b. 5
c. 9
d. 10
15. Which statements about mixtures are correct?
I. The components may be elements or compounds. True
II. All components must be in the same phase.
False because Heterogenous Mixtures can
have different phases
III. The components retain their individual properties. True
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a. I and II only
b. I and III only
c. II and III only
d. I, II and III
II.
SHORT ANSWERS: Use only the space provided for your answers.
16. State the balanced equation (including state symbols) for the following reactions.
a. The addition of aqueous hydrochloric acid (HCl) to solid calcium
carbonate to give aqueous calcium chloride, carbon dioxide and water.
2HCl (aq) + CaCO3 (s) = CaCl2 (aq) + H2O (l) + CO2 (g)
b. The reaction between ammonia gas and oxygen gas to give nitrogen(II) oxide gas and
water.
2NH3 (g) + 5/2O2 (g) = 2NO (g) + 3H2O (l)
Multiplying the chemical equation by a factor of 2 (where 2 is the denominator of the
coefficient of O2),
4NH3 (g) + 5O2 (g) = 4NO (g) + 6H2O (l)
Note: nitrogen (II) oxide means nitrogen(II) ion forms a compound with oxide ion, that is,
N2+ + O2-  N2O2  NO
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17. Stearic acid is a waxy solid and a useful type of saturated fatty acids that comes from
many animal and vegetable fats and oils. The diagram below shows the cooling curve of
stearic acid.
Melting
70 oC
Point
Phase Change
Solid
i. Determine the melting point of stearic acid.
The melting point of stearic acid is about 70 oC
ii. Explain why the temperature remains constant between B and C.
The temperature remains constant between B and C because it takes longer time for the
solid stearic acid to be completely melted. Moreover, melting is an endothermic process
meaning energy is absorbed to but this amount of energy is used up during the phase
change and not to increase the temperature of the stearic acid. The phase change stops
until such time that all solid stearic acid is converted completely into its liquid state.
18. Methane, (CH4) is a colourless, odourless gas that occurs abundantly in nature and as
a product of certain human activities. Deduce the:
i.
total number of atoms in one molecule of methane.
In 1 molecule of methane, there are 1 C atom and 4 H atoms so there are a total of 5 atoms.
ii. total number of atoms in one mole of methane.
Calculate the number of methane molecules
molecules
 6.022  1023 molecules
mole
Calculate the number of atoms. Using the result in part (i) above, there are 5 atoms in a
molecule of methane,
5 atoms
6.022  1023 molecules 
 30.11  1023 atoms  3.011  1024 atoms
molecule
1 mole  6.022  1023
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iii. amount in moles of 1.605 g of methane.
Calculate the molar mass of methane CH4.
Molar Mass  (1)(12.01)  (4)(1.01)  16.05
g
mol
Calculate the moles of 1.605 g CH4
Moles  1.605 g 
1
g
16.05
mol
 0.1000 mol
Remarks:
 Mole to Mass (g): Multiply the given moles by molar mass
 Mass (g) to Mole: Divide the given mass (g) by the molar mass
iv.
write the complete and balanced equation for the incomplete combustion of methane.
Incomplete combustion (where there is not enough oxygen present) can lead to the formation of
carbon or carbon monoxide.

With little oxygen
CH4 + O2 = C + 2H2O

With some oxygen
2CH4 + 3O2 = 2CO + 4H2O
Note that there is not only one equation for incomplete combustion, whereas there can only be
one equation for complete combustion.
Complete Combustion
CH4 + 2O2 = CO2 + 2H2O
19. List 3 laboratory safety measures you need to observe when measuring volume of acid
using a graduated cylinder.
1. Wear laboratory gown, goggles or face shield, and latex gloves (personal protective
equipment or PPE) to avoid direct contact in case of accidental spill.
2. If the acid is from a big container, transfer a sufficient amount into a beaker first before
transferring into the graduated cylinder. This way accidental spillage can be prevented
3. Some concentrated acids emit fumes so transferring to graduated cylinder should be done
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inside a fume hood.
Fume Hood
4. In case the graduated cylinder breaks causing spillage of the acid, the acid should be
neutralized using a base solution (such as caustic solution) to convert the acid to salt and water
(which relatively safer than the acid). Then use rag to wipe the spillage and the broken glass
can be swept using broom and pan.
20. A student needs to measure 4.00g of CaCO3 (calcium carbonate). However, the
substance inside the bottle are in big lumps (granules) of solids. Name 2 apparatus
(laboratory instrument) the student will need to be able to correctly measure the mass of
CaCO3.
First, the student needs to pulverize or grind the CaCO3 lumps into powder using a clean
mortar and pestle. Then place a weighing paper on an analytical balance or a top-load
balance whose smallest scale is 0.01 g. Using a laboratory spatula or spoon, measure 4.00 g of
the CaCO3 powder.
Apparatus/Instrument:
1. Mortar and pestle
2. Analytical balance or top-loading balance
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Top loading balance
Readability 1 g
Example 1 g 2 g 3 g
Readability 0.1 g
2.1 g 4.5 g 10.5g
Readability 0.01 g
4.00g 5.05 g 6.14g
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