NOTES – MOLAR MASS AND MOLE CONVERSIONS
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|UNIT 4 CHEMICAL REACTIONS: THE MOLE, STOICHIOMETRY AND THERMODYNAMICS |
|Part A: The Mole |
|Big Picture Ideas: |
|The mole is a unit of count. |
|Using conversion factors, one can convert between mass, moles, particles and volume for a given substance. |
|Empirical data including percent composition can be used to determine chemical formulas. |
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|Big Picture Questions: |
|How do chemists count particles? |
|How do chemists convert between mass, moles, particles and volume for a given substance? |
|How do chemists determine chemical formulas? |
|Suggested Resources |
|Homework Assignments |
|Classwork Assignments |
|Laboratory Activities |
|Formative Assessments |
|Textbook pages: Chapter 10 |
|Websites: |
Key Terms
1. mole
2. Avogadro’s number
3. atomic mass
4. formula mass
5. molecular mass
6. molar mass
7. molar volume
8. percentage composition
9. empirical formula
10. molecular formula
11. STP conditions
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CALCULATING MOLAR MASS OF COMPOUNDS
a. sodium hydroxide
b. calcium cyanide
c. magnesium phosphate
d. iron (III) dichromate
PERCENT COMPOSITION
a. Find the percent composition of calcium cyanide
Formula: __________________________
% Ca = __________
% C = __________
% N = __________
How many grams of calcium are in 40.0 g of calcium cyanide?
b. Find the percent composition of magnesium phosphate
Formula: __________________________
% Mg = __________
% P = ___________
% O = ___________
How many grams of magnesium are in 350 g of magnesium phosphate? ___________________
** What mass of magnesium phosphate contains 15 g of magnesium? ___________________
TRY
1. Find the molar mass of each compound below
a. lithium carbonate ____________________
b. calcium nitrate _____________________
c. tin (IV) sulfate ______________________
2. Find the percent composition of tin (IV) sulfate
% Sn = __________
% S = __________
% O = __________
How many grams of tin are in 250 g of tin (IV) sulfate?
MOLE CONVERSIONS
1. Find the molar mass of each compound below
a. diphosphorus pentoxide ______________
b. copper (II) sulfate _____________
c. calcium cyanide _____________
d. aluminum nitrate _____________
MOLE CONVERSIONS
6.02 x 1023 molecules = 1 mole
6.02 x 1023 formula units = 1 mole
molar mass in grams = 1 mole
1. Find the mass of 4.50 moles of diphosphorus pentoxide _____________
2. How many moles is 250.0 g of copper (II) sulfate? _____________
3. Find the mass of 0.545 moles of calcium cyanide ______________
4. How many molecules are in 110 g of diphosphorus pentoxide? _______________
Make the following mole conversions.
STEP 1: Write the correct formula
STEP 2: Determine the molar mass
STEP 3: Use dimensional analysis to convert
a. 575 g of sodium sulfate to moles ________________
b. 0.025 moles of phosphorus pentachloride to grams ________________
c. 15.0 g of iron (III) nitrate to moles ________________
d. 8.02 x 1023 molecules of carbon disulfide to grams ________________
MOLES AND VOLUME
Avogadro’s hypothesis:
STP:
Make the following mole conversions.
a. 14.0 L of nitrogen gas at STP to moles
b. 2.5 g of chlorine gas at STP to molecules
c. 2.24 x 1025 atoms of neon at STP to liters
d. 13.3 L of fluorine gas at STP to grams
EMPIRICAL AND MOLECULAR FORMULAS
a. Find the percent composition of C2H4
%C = _______
%H = _______
b. Find the percent composition of C5H10
%C = _______
%H = _______
empirical formula: ________________________________________
molecular formula: ________________________________________
Determine the empirical formula of each compound below
a. P4O10 b. C6H12O6 c. C3H6O
1. The empirical formula of a compound is CH2O. Its molar mass is 360 g/mol. Find its molecular formula.
2. The empirical formula of a compound is P2O5. Its molar mass is 284 g/mol. Find its molecular formula.
HOMEWORK - MOLAR MASS AND % COMPOSITION PRACTICE PROBLEMS
1. Label each compound below as ionic or covalent. Write the formula and determine the molar mass of each compound.
|compound |ionic/ |formula |molar mass |
| |covalent? | | |
| | | | |
|barium sulfate | | | |
| | | | |
|tricarbon octahydride | | | |
| | | | |
|iron (III) carbonate | | | |
| | | | |
|tetraphosphorus decoxide | | | |
| | | | |
|strontium phosphate | | | |
2. Find the percent composition of iron (III) carbonate.
% Fe =
% C =
% O =
3. How many grams of iron are in 125 g of iron (III) carbonate?
4. What mass of iron (III) carbonate contains 10.0 g of iron?
HOMEWORK - PERCENT COMPOSITION
Determine the percent composition of each of the compounds below:
1. KMnO4
% K = ______________
% Mn = _____________
% O = ______________
2. HCl
% H = ______________
% Cl = ______________
3. Mg(NO3)2
% Mg = _____________
% N = ______________
% O = ______________
4. (NH4)3PO4
% N = _____________
% H = ______________
% P = ______________
% O = ______________
5. Al2(SO4)3
% Al = ______________
% S = ______________
% O = ______________
Solve the following problems
6. How many grams of oxygen can be produced from the decomposition of 100 g of KClO3?
7. How much iron can be recovered from 25.0 g of Fe2O3?
8. How much silver can be produced from 125 g of Ag2S?
HOMEWORK - PRACTICE CONVERSIONS
1. Write the formula for each compound below. Then determine its molar mass.
| |formula |molar mass |
|calcium sulfate | | |
|aluminum cyanide | | |
|phosphorus triiodide | | |
2. Use the molar masses you found in # 1 to make the following conversions:
a. Find the mass of 1.25 moles of calcium sulfate.
b. How many moles is 2.50 g of aluminum cyanide?
c. Find the mass of 0.750 moles of phosphorus triiodide.
d. How many molecules is 12.50 g of phosphorus triiodide?
e. Find the number of formula units in 10.0 g of calcium sulfate.
HOMEWORK - MIXED MOLE CONVERSIONS
1. Convert the quantities below to moles
a. 14.0 g of lead _____________________
b. 20.5 g of lithium hydroxide ______________________
c. 14.0 L of oxygen gas at STP _______________________
2. Find the mass of
a. 10.0 L of hydrogen gas at STP _______________________
b. 3.21 x 1022 molecules of carbon tetrachloride _______________________
3. Find the empirical formula of each compound below
a. C4H8 b. C12H24O12 c. Si3N4 d. C4Cl10
4. Find the molecular formula if the empirical formula is C3H8 and the molar mass is 132 g/mol.
5. Find the molecular formula if the empirical formula is N2O5 and the molar mass is 216 g/mol.
LAB: PERCENT SUGAR IN BUBBLE GUM NAME:
BACKGROUND: In this lab you are going to design and carry out an experiment to determine the percentage of sugar in bubble gum. To do so, you will assume that all of the flavoring removed from bubble gum during chewing is sugar. The chemical formula for sucrose, the sugar in bubble gum, is C12H22O11. After determining the percentage of sugar in bubble gum, you will then determine the mass of carbon and the number of carbon atoms in the sugar in a piece of bubble gum.
PROCEDURE: Write out the procedure you will follow in the space below. Include all details.
DATA: Set up a data table in the space below to record all necessary data.
CALCULATIONS: Show and explain all work. Calculations must be neat and easy to follow.
a. mass of sugar in your piece of gum (show calculation!)
b. mass of gum alone (without wrapper) (show calculation)
c. average % sugar in bubble gum (show calculation based on your data!)
d. % carbon in sugar (C12H22O11) (show calculation – use your class notes on % composition)
e. mass of carbon in the sugar in your piece of bubble gum (show calculation, use class notes)
(HINT: How many grams of sugar were in your gum? What per cent of sugar is carbon?)
f. atoms of carbon from the grams you calculated in “d” (show calculation, g carbon to atoms)
CONCLUSIONS:
1. What did you learn from this experiment?
2. List two sources of error and describe the effect each had on your results. (Would the error make the per cent sugar reported too high or too low and why).
a.
b.
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UNIT 4: CHEMICAL REACTIONS, STOICHIOMETRY AND THERMODYNAMICS.
PART A: MOLAR MASS & PERCENT COMPOSITION
How many is a mole? 6.02 x 1023 atoms or molecules = 1 mole
How heavy is a mole? molar mass in grams = 1 mole
How much space does a mole occupy? for a gas at STP 22.4 L = 1 mole
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