Unit 4 Packet - Page 16 of 16
Honors Chemistry - Unit 4
The Mole – Math with Chemical Formulas
Vocab Assignment Due: Mole Day Project:
Problem Set Due: Test Date:
VOCABULARY Assignment
(Use Making Concept Maps (handout) to assist you in making a Concept Map from these vocabulary items/concepts):
molecular mass formula mass hydrate
Avogadro’s number (constant) mole Molarity
percent composition empirical formula molecular formula
formula unit ionic compound molecular compound
FORMULA/CONSTANTS to be memorized
Molar mass conversion
*Avogadro’s number
*Molarity
Steps for empirical formula/ molecular formula problems
OBJECTIVES:
· Be able to perform math functions with and without your calculator using correct scientific notation.
· Be able to find molecular/formula mass using the periodic table.
· Be able to calculate Molarity.
· Be able to calculate percent composition.
· Be able to determine empirical and molecular formulas using lab data.
Percent to mass; mass to mole; divide by small; multiply to whole!
· Understand the mole and Avogadro’s number.
· Be able to convert to/from atoms, ions, molecules, moles and grams.
Unit 4 PROBLEM SET – The Mole – Math with Chemical Formulas:
- Show your work on all problems. Credit will not be given without work.
- Include units on your answers.
Review Questions:
1. Name the following compounds:
a. Ba(C2H3O2)2
b. Sn(NO2)2
c. P3S2
d. CrPO4
2. Write formulas for the following:
a. copper (II) nitrate
b. carbon tetrabromide
c. strontium chloride
d. iron (III) sulfate
Current Unit Material:
3. Aspartame, the artificial sweetener marketed under the name NutraSweet, has a molecular formula of C14H18N2O5.
A. What is the mass of 2.00 mol of aspartame?
B. How many moles are present in 5.67 g of aspartame?
C. What is the mass, in grams, of 0.224 mol of aspartame?
D. How many hydrogen atoms are present in 2.13 mg of aspartame?
4. The koala bear dines exclusively on eucalyptus leaves. The chief constituent in eucalyptus oil is a substance called eucalyptol, which contains 77.87 % C, 11.76 % H and the remainder O. If the molecular weight of eucalyptol is 154 amu, what is the empirical and molecular formula of this compound?
5. Convert 2.75 x 1010 molecules of CO2 to moles. What is the mass of this quantity?
6. How many grams of solute are present in 75.0 ml of 1.33 M CoSO4?
7. How many milliliters of 0.650 M NiCl2 contains 1.70 g of solute?
Extra Credit: Glycerol, C3H8O3, is a substance used extensively in the manufacture of cosmetics, foodstuffs, antifreeze, and plastics. Glycerol is a water-soluble liquid of density 1.2656 g/ml at 15 0C. Calculate the molarity of a solution of glycerol made by dissolving 30.000 ml glycerol at 15 0C in enough water to make 275.00 ml of solution.
Guided Note-Taking for THE MOLE!
What is a mole?
l “Official Definition”
l the amount of a substance that contains as many particles as there are atoms in exactly 12g of carbon-12
l A mole is a counting unit
l just like a dozen
l other examples…..
Avogadro’s Number
l Constant
l the number of particles in exactly one mole of a pure substance
6.02 X 1023
Memorize this Number
1 mol = 6.02 X1023 of anything
But most often the mole is used with atoms, ions, formula units or molecules
Examples of Conversion Factors:
1 mol
6.02 X 1023 atoms
1 mol
6.02 X 1023 ions or formula units
1 mol
6.02 X 1023 molecules
Molar Mass
l Mass in g of 1 mole of anything
l For , the is equal to the .
l 1 mol
atomic wt. (g)
Molar Mass Examples: 1 mol C and
12.0 g C
You try:
1 mol Ca 1 mol Fe
g Ca g Fe
Now, you have Two conversion Factors for a mole…..
Avogadro’s number Molar mass
1 mol and 1 mol
6.02 X 1023 atoms, ions, formula units, or molecules ? g
Example 1
How many g in 2.0 mol of He?
Example 2
How many moles in 3.01 X 1023 atoms Ag?
Example 3
What is the mass of 1.20 X 108 atoms of Cu??
You try:
Convert 11.5 g B to moles B
Convert 8.0 X 1019 atoms of Ag to g
Formula Mass/Molecular Mass/Molar Mass
l Sum of masses in a compound
Example: Molar Mass of sodium chloride NaCl
Example: Molar Mass of Ca(NO3)2
You try: Calculate the molar mass of sodium phosphate Na3PO4
These can be used as conversion factors!
1 mol NaCl
58.44g NaCl
1 mol MgCl2
95.21g MgCl2
1 mol Ca(NO3)2
164.1g Ca(NO3)2
Example: How many mol in 127g barium chloride?
Guided Note-Taking on Percent Composition
l Percent composition is the percent by mass of each element in a compound.
l Percent composition is the same, regardless of the size of the sample.
Percent Composition Calculations
% comp = mass of element X 100%
molar mass of cpd
= % element in the compound
Example: Find the % composition of Cu2S
l First, find the molar mass:
l Next, find the % of each element
l Next, check your work – do the %s add up to 100?
You try:
1) barium chloride
Answer: barium 65.90%; chloride 34.10%
2) sodium phosphate
Answer: sodium 42.07%; phosphorus 18.89%; oxygen 39.04%
Guided Note-Taking on Empirical Formulas
l Empirical Formula = Simplest Formula
To find the empirical formula from data:
1. Assume 100% sample; change % to grams for each element
2. Find moles from the grams of each element
3. Find the smallest whole # ratio by dividing by the smallest number of moles
4. If necessary, multiply to get rid of fractions.
Example 1: A compound is 78% B and 22% H. What is the empirical formula?
First, change % to grams and find moles:
Next, divide all mole numbers by the smallest number of moles:
Finally, use these whole numbers as the number of each individual element. They are the subscripts.
Example 2:
l Analysis shows a compound to contain 26.56% K, 35.41% Cr, and 38.03% O. Find the empirical formula of this compound:
l First (always!) assume 100g sample, convert % to g and then find moles of each element.
Next, Conversion to moles:
Next, divide all numbers by the smallest whole number to find the smallest whole number ratios:
l So, if you have: multiply all by:
.25 or .75 4
.33 or .66 3
.50 2
l For our example:
You Try:
What is the empirical formula if we have a sample containing 66.0% Ca and 34.0% P?
Answer: Ca3P2
You Try:
Find the empirical formula of a compound with 32.38% Na; 22.65% S; and 44.99% O.
Answer: Na2SO4
Molecular Formula
Molecular Formula = Actual Formula
Example:
C2H6 CH3
molecular empirical
MF = (EF)x where X = Molecular mass
Empirical mass
Example:
The empirical formula of a compound was found to be P2O5. Experimentation shows that the molar mass of this compound is 283.89 g/mol. What is the compound’s molecular formula?
Guided Note-Taking on Moles in Solution (Molarity)
l Molarity is the term used for moles dissolved in solution
l Symbol for Molarity = M
l Definition – moles of solute per liter of solution
l Formula
M = moles solute (mol)
liter solution (L)
Example 1: What is the molarity of a 0.5L solution containing 2 moles of NaCl?
Example 2:
What is the molarity of a 250 mL solution containing 12.7 g of lithium bromide?
Example 3: How would you make 500mL of a 0.32M solution of LiBr and water?
You try:
1) Calculate the M of a 700. mL solution of 23.2g calcium chloride
2) How would you make a 0.2 L solution of 0.50 M CaCl2 solution?
CONVERSION WORKSHEET NAME:______
A. Convert the following:
1. 1.20 x 1025 atoms of N to moles
2. 11.5 g of carbon to moles
3. 1.00 x 1026 atoms of Tl to grams
4. 0.400 moles of Cd(IO3)2 to formula units
5. 76.0 g of Ca to moles
6. 46.0 g of potassium nitride to formula units
7. 1.00 x 1023 formula units of CsBr to grams
8. 3.00 moles of Cl to grams
9. 9.30 moles of carbon dioxide to molecules
10. 8.00 x 1019 formula units of copper (II) sulfate to grams
11. 34.2 g of trisulfur dioxide to moles
12. 3.01 x 10 23 atoms of Mg to moles
13. 2.1 g of Ni to atoms
B. Molarity Practice
14. What is the molarity of the following?
a. 5.23 g Fe(NO3)2 in 100 ml of solution.
b. 8.55 g of ammonium iodide in 0.5 L of solution.
c. 3.2 kg of cobalt (II) sulfate in 4.3 L of solution.
15. Describe the preparation of the following:
a. 200 ml of 3.0 M NiCl2
b. 1 L of 1.5 M AgF
Chapter Seven– Practice Sheet
CONVERSIONS
1. How many moles is 23.8 g of dinitrogen pentoxide?
2. How many formula units in 27 moles of iron (II) acetate?
3. How many g in 2.5 x 10 21 formula units of Calcium chloride?
4. How many molecules in 32.5 g of water?
PERCENT COMPOSITION
Find the percent composition of the following:
5. KNO3
6. Mg(NO3)2
7. The % of O in CuSO4
Empirical, Molecular, and Molarity
8. Analysis of a sample of sulfuric acid shows it to contain 0.17 g of hydrogen, 2.82 g of sulfur, and 5.67 g of oxygen. What is the empirical formula for this compound?
9. Analysis of a salt results in the following composition: 3.47 g of Na, 2.12 g of N and 7.27 g of oxygen. What is the simplest formula of this salt?
10. A barium salt is found to contain 21.93 g of barium, 5.12 g of sulfur and 10.24 g of O. What is the empirical formula?
11. A compound contains: 26.7 % C, 2.2 % H and 71.1 % O. The molecular weight of the compound is 90. What is the compound’s molecular formula?
12. A certain compound contains only C, H, and O. If 54.6 % is C and 9.0 % is H and the molecular weight is 176, what are the compounds empirical and molecular formulas?
13. The percentage composition of ethane gas is 80.0 % C and 20.0 % H. The molecular weight for ethane is 30. What is the molecular formula for this compound?
14. What is the M of 32.3 g of calcium chloride in 750 ml of solution?
15. How do you prepare 600 ml of 1.25 M CuO ?
REVIEW – Chemistry Unit Five
1. How many moles are present in 114.95 g of nitrogen dioxide?
2. How many moles of nitrate are present in one mole of magnesium nitrate?
3. How many formula units in 64.3 g of lithium sulfate?
4. What is the molarity of 9.94 g of cobalt (II) sulfate in 250. ml of solution?
5. How would you prepare 250. ml of a 0.002 0 M solution of Cd(IO3)2?
6. What is the percentage of nitrogen in urea, CO(NH2)2?
7. A compound contains 27.3 g of C and 72.7 g of O. What is the empirical formula for this compound?
8. Benzoic acid is a compound used as a food preservative. The compound contains 68.8 % C, 4.95 % H and 26.2 % O by mass. What is the compound’s empirical formula?
9. Ascorbic acid, also known as Vitamin C, has a percentage composition of 40.9 % carbon, 4.58 % hydrogen, and 54.5 % oxygen. Its molecular mass is 176.1 u. What is its molecular formula?
ANSWERS:
1. 2.5 mol NO2
2. 2 moles
3. 3.52 x 1023 formula units Li2SO4
4. 0.257 M CoSO4
5. Add 0.231 g of Cd(IO3)2to enough water to make 250. ml of solution.
6. 46.7 % N
7. CO2
8. C7H6O2
9. C6H8O6