School of Chemistry and Physics, Howard College Campus
University of KwaZulu-Natal
SPECIAL SCIENCE CHEMISTRY (CHEM100): 2014
Additional Tutorial 1 ANSWERS
1.
2.
Complete the following conversions:
(i)
1.265 g
=
1.265  103 mg
(ii)
125 mL
=
0.125 L
(iii)
1.50 atm
=
1140 mmHg
(iv)
2.25 L
=
2.25  103 cm3
Convert a temperature of
(i)
329 K to °C
56°C
(ii)
42°C to K
315 K
3.
Determine the formula mass of a sample of K2Cr2O7 and calculate the percentage composition of K, Cr
and O in K2Cr2O7.
Formula Mass = 2(39.10) + 2(52.00) + 7(16) = 294.2
%K = 2(39.10)/ 294.2 = 26.58%
%Cr = 35.35%
%O = 38.07%
4.
Give the number of electrons, protons and neutrons in the atoms of
electrons = 46, protons = 48 and neutrons = 67
1
.
5.
Balance the following equations
(a)
C4H10(g) + 13/2 O2(g) → 4 CO2(g) + 5 H2O(g)
(b)
2 Al(s) + 3 Cl2(g) → 2 AlCl3(s)
(c)
2 Ag(s) + Cu2+ → 2 Ag+ + Cu(s)
(d)
C2H5OH + O2  CO2 + H2O
C2H5OH + 3 O2  2 CO2 + 3 H2O
(e)
Mg + H3PO4  Mg3(PO4)2 + H2
3 Mg + 2 H3PO4  Mg3(PO4)2 + 3 H2
(f)
H2SO4 + NaHCO3  Na2SO4 + CO2 + H2O
H2SO4 + 2NaHCO3  Na2SO4 + 2CO2 + 2H2O
6.
Calculate the number of calcium atoms in 0.25 mol of calcium phosphate, Ca 3(PO4)2.
Number of calcium atoms = 3  0.25  6.022  1023 = 4.52  1023
2
Additional Tutorial 2 ANSWERS
1.
Helium (He) is a valuable gas used in industry, deep-sea diving tanks and balloons. How many moles of
He atoms are there in 6.46 g of He?
n = m/MM = 6.46 g/ 4.00 g mol-1 = 1.615 mol
2.
Zinc (Zn) is a silvery metal that is used in making brass (with copper) and in plating iron to prevent
corrosion. How many grams of zinc are in 0.356 mole of Zn?
m = n  MM = 0.356 mol  65.39 g mol-1 = 23.28 g
3.
Sulfur (S) is a nonmetallic element present in coal. When coal is burned, sulfur is converted to sulfur
dioxide and eventually sulfuric acid that give rise to the acid rain phenomenon. How many atoms are in
16.3 g of S?
Number of moles of S = 16.3 g/32.07 g mol-1 = 0.5083 mol
Number of atoms of S = 0.5083  6.022  1023  1= 3.061  1023
4.
5.
Calculate the molecular masses in (a) sulfur dioxide (SO2) and (b) caffeine (C8H10N4O2).
(a)
MM = 32.07 + 2(16) = 64.07
(b)
MM = 8(12.01) + 10(1.01) + 4(14.01) + 2(16) = 194.22
Calculate the percent composition by mass of H, P, and O in phosphoric acid (H3PO4).
MM of phosphoric acid = 98
% H = 3.1%, % P = 31.6% and % O = 65.3%
3
6.
Chalcopyrite (CuFeS2) is a principal mineral of copper. Calculate the number of kilograms of Cu in 3.71
 103 kg of chalcopyrite.
% Cu in chalcopyrite = (63.55/183.54)  100% = 34.6%
 Mass of Cu in chalcopyrite = 34.6%  3.71  103 = 1.28  103 kg
7.
Classify each of the following species in aqueous solution as a Brønsted acid or base: (a) HBr,
(b)
NO2- and (c) HCO3(a)
8.
acid
(b)
base
(c)
acid
Calculate the number of moles in 12.2 g of K2Cr2O7.
n = m/MM = 12.2 g/294.2 g mol-1 = 0.04147 mol
9.
Using the ideal gas equation, calculate the volume of 2.36 moles of PCl3 exerting a pressure of 1.69 atm
at 55.2 °C.
V = nRT/P = 2.36 mol  0.08206 L atm K-1 mol-1  328.2 K/1.69 atm
= 37.6 L
4
Additional Tutorial 3 Answers
1.
Name the following compounds:
(a)
H
H
CH3 H
H
H
C
C
C
C
C
H
H
H
H
H
(b)
H
H
2-methylpentane
(c)
H
H
CH3 H
H
H
H
C
C
C
C
C
C
H
H
H
CH3 H
H
2,4-dimethylhexane
H
CH3 H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
(d)
H
OH
H
H
H
O
C
C
C
C
H
H
H
5-methylhexanol
butanal
O
(e)
H
H
H
H
(f)
H
C
C
C
C
H
Cl
H
H
C
OH
H
2-chlorobutane
(g)
H
benzoic acid
H
H
H
H
H
O
C
C
C
C
C
C
H
H
H
H
H
O
H
H
C
C
H
H
ethylhexanoate
(h)
H
H
H
H
C
C
C
H
H
H
O
H
H
H
C
C
C
H
H
H
dipropylether
5
H
H
H
H
Cl
(i)
CH3
1-chloro-2-methylbenzene
2.
Give the structures for the following compounds:
(a)
2,3-dimethylpentane
H
(c)
H
(e)
(b)
H
H
CH3 H
H
C
C
C
C
C
H
CH3 H
H
H
3-bromo-2-methylhexane
H
H
octanoic acid
(d)
H
H
H
H
H
H
H
O
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
Br
H
H
H
C
C
C
C
C
C
H
CH3 H
H
H
H
ethylmethyl ether
H
OH
H
H
C
C
H
H
H
O
H
1,3-dichlorobenzene
Cl
Cl
(f)
2,2-dimethylheptane
H
(g)
H
CH 3 H
H
H
H
H
C
C
C
C
C
C
C
H
CH 3 H
H
H
H
H
H
5-bromo-7-methyloctanoic acid
H
H
CH 3 H
Br
H
C
C
C
C
C
H
H
O
C
C
C
H
H
6
H
H
H
H
H
C
OH
H
H