Download Extra Practice Questions: Molar Mass and Conversions

Student Worksheet 4.4A
Extra Practice Questions: Molar Mass and Conversions
1. Determine the molar mass of each of the following substances.
(a) MgI2(s)
(b) Al(OH)3(s)
(c) (NH4)2CO3(s)
(d) CoCl2•6H2O(s)
2. Convert each of the following masses into an amount in moles of the given substance.
(a) 8.40 g of NaOH(s)
(b) 4.2 kg of H2O(l)
3. Convert each of the following amounts into a mass in grams of the given substance.
(a) 0.456 mol of Al2(SO4)3(s)
(b) 0.518 mmol of CuSO4•5H2O(s)
4. Complete the following table.
Substance
Molar Mass (g/mol)
CaCl2(s)
Mass (g)
18.6
Al2O3(s)
Mg(OH)2(s)
Na2CO3•10H2O(s)
2-4 Unit 2 Lab and Study Masters
Amount (mol)
0.267
35.00
0.150
Copyright © 2002 Nelson Thomson Learning
Student Worksheet 4.4C
Extra Practice Questions: Number of Atoms and Molecules
By using Avogadro’s constant NA as a conversion factor one can predict the number of atoms, molecules,
or most anything in an amount (in moles). Quite often this number is meaningless because the human mind
is not capable of visualizing/comprehending such large numbers, but the calculation can be done. Some
people call this calculation “exam chemistry” because you might find it on exams but it does not have any
other use. A couple of examples and some typical questions are provided below. (The SI symbol for amount
is n and for number of entities is N. Appendix E, page 755, provides you with information on inputing scientific notation into your calculator and on expressing certainty in significant digits. Further practice is available on Molar Mass and Conversions and the Factor-Label Method in the enrichment exercises.)
Example
(a) Predict the number of carbon atoms in a 2.06 g sample of carbon from a
graphite pencil lead.
1 mol
6.02 1023
NC 2.06 g 1.03 1023
12.01 g
1 mol
In a typical calculator enter: 2.06 12.01 6.02 EXP 23 .
(b) Predict the number of carbon dioxide molecules in 0.37 g of exhaled
carbon dioxide.
1 mol
6.02 1023
NCO 0.37 g 5.1 1021
2
44.01 g
1 mol
(c) Predict the mass of 6 million water molecules in a small drop of water.
1 mol
18.02 g
mH O 6 106 2 1016 g
2
1 mol
6.02 1023
In a typical calculator enter: 6 EXP 6 6.02 EXP 23 18.02 .
Complete the following questions concerning the number of atoms or molecules in a sample of a chemical.
Communicate your problem-solving approach by using SI symbols (make your answer as internationally
understood as possible) and express your answer to the correct certainty by rounding your answer to the
correct number of significant digits.
1. Predict the number of gold atoms in a 20 g ring.
2. Predict the mass of 52 quadrillion silver atoms. (Enter the equivalent of 52 EXP 15 in your calculator.)
3. Predict the mass of exactly one table sugar (sucrose) molecule.
4. Predict the number of water molecules in a full cup (250 mL or 250 g) of water.
2-6 Unit 2 Lab and Study Masters
Copyright © 2002 Nelson Thomson Learning
Student Worksheet 5.4A
Extra Practice Questions: Gravimetric Stoichiometry
Complete the following stoichiometric problems. All answers should be expressed to the correct
number of significant digits.
1. Calculate the mass of iron(III) oxide (rust) produced by the reaction of 500 g of iron with oxygen
from the air.
2. What mass of precipitate should form if 2.00 g of silver nitrate in solution is reacted with excess
sodium sulfide solution?
3. Determine the mass of water vapor formed when 1.00 g of butane, C4H10(g), is burned in a lighter.
4. Silver metal can be recovered from waste silver nitrate solutions by reaction with copper metal.
What mass of silver can be obtained using 50 g of copper?
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Unit 2 Lab and Study Masters
Copyright © 2002 Nelson Thomson Learning
Student Worksheet 5.6A
Extra Practice Questions: Applications of Stoichiometry
1. In a chemical analysis to test the purity of a bottle of sodium bromide, a solution containing
1.17 g of sodium bromide was reacted with an excess of dimercury(I) acetate solution. The dry
precipitate had a mass of 2.73 g. Calculate the percent yield for the precipitate and comment on
the purity of sodium bromide.
2. A solution containing 2.56 g of aluminum nitrate is mixed with a solution containing 1.02 g
of ammonium sulfide. Determine the unreacted mass of the excess reagent and the mass of precipitate formed.
Copyright © 2002 Nelson Thomson Learning
Unit 2 Lab and Study Masters
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