The Mole
Molar Mass in Grams = 1 Mole = 6.02 x 1023 atoms/molecules
NOTES:
NOTES:
Sig Figs
Significant Figures
1. All non zero numbers are always significant
2. Zero is significant if:
a. it is sandwiched between nonzero digits
ex: 78.005
b. it is the last digit and there is a decimal
ex: 5.870 or 5600.
Zero’s after a non-zero number count only if there is a decimal.
Zero’s at the beginning of a decimal never count!!
Underline and state the total number of significant figures in each of the following:
1. 234
14. 123.45
2. 23.465
15. 12335345
3. 12.012
4. 56700
5. 409
6. 0.00045
7. 68,000
8. 68.000
9. 68,000.
10. 235.0060
11. 0.000456
16.
17.
18.
19.
20.
21.
22.
23.
24.
0.1234
6.03070
0.0004
89004
506090040
3.00060
4.56700
123.005
4500.
12. 0.0050060
13. 45708
25. 40.0
26. 400
Round each of the numbers shown below to the number of significant figures indicated in the
parentheses.
27. 105.762 (4) _____________
34. 23,443 (2) _____________
28. 0.00717 (2) _____________
35. 234.9
(3) _____________
29. 0.5166 (3) _____________
35. 699.9
(3) _____________
30. 0.0502 (2) _____________
37. 345.566 (4) _____________
31. 27.155 (3) _____________
38. 56,678 (3) _____________
32. 2,005.02 (5) _____________
39. 304.00 (4) _____________
33. 450.679(5) _____________
40. 567,457 (2) _____________
Rules for Significant Figures in Calculations
1. Multiplication/ Division
The answer can have no more sig figs than the least precise measurement
used in the calculations.
ex: 9.325 x 1.2 = 11.19 = 11
1.2 has the least number of sig figs (2) so the answer can only have 2 sig figs.
ex: 124.6 / 7 = 17.8 = 20
7 has the least number of sig figs (1) so the answer can only have 1 sig figs.
2. Addition/Subtraction
The answer has the same number of decimal places as the least precise
measurement used in the calculation.
ex: 12.15
1.1
+ 3.125
16.375 = 16.4 the answer is in the tens place since that is the least number
of decimal places
ex:
3.0 - 0.25 = 2.75 = 2.8 the answer is in the tens place since that is the least
least number of decimal places
Solve the following problems. Round all to the appropriate number of sig figs.
1. 709.8 x 23.45 =
11. 2.34 + 0.034 =
2. 23.4 x 6.7 =
12. 345 + 234.0 =
3. 0.0034 x 3.0 =
13. 234.5 + 3.45 =
4. 567 x 2.3 =
14. 34.0 + 23.27 =
5. 3.04 x 0.083 =
15. 23.457 + 0.1 =
6. 457/ 5.0 =
16. 46.4 - 3.060 =
7. 973/ 85 =
17. 305 – 23.4 =
8. 0.023 / 0.04 =
18. 0.035 - 0. 017 =
9. 17364 / 482 =
19. 234.56 - 34.467 =
10. 8473652 / 7002 =
20. 747.00 - 700.0 =
Molar Mass / Molecular Weight
I. Calculate the molar mass for each of the following elements or compounds. Include
all units. YOU MUST SHOW ALL WORK TO RECEIVE CREDIT.
II. For each compound calculate the percent composition of the first element in the
formula.
1. iron
2. chromium
3. chlorine gas
4. water
5. SiO2
6. H3PO4
7. iron (II) sulfate
8. ammonium phosphate
9. Cu(NO3)2
10. CH3COOH
(calculate % of all carbon)
11. magnesium chloride
12. mercury (II) oxide
13. Al2(SO4)3
14. C12H22O11
15. copper (I) iodide
16. potassium nitrate
17. tetraphosphorus decoxide
18. cobalt (I) carbonate
19. calcium thiocyanate
20. tin (II) hydroxide
NOTES:
Mole Conversions
C11 Honors
Re: 11/2011
MOLE FUN
Answer each of the following using the factor-label method to the correct number of
significant figures.
1. If 2.55 moles of hydrogen react in an experiment, how many grams of hydrogen react?
2. How many grams are in a 0.625 mole sample of calcium hydroxide?
3. How many molecules are in a 29.42 gram sample of barium nitrate?
4. How many moles of octane(C8H18) are in 9.25 x 1032 molecules of C8H18?
5. How many grams are in 2.87moles of cobalt(III) nitrate?
6. Caffeine has the molecular formula, C8H10O2N4. Calculate the mass in grams of 1.20 x 10-2
moles of caffeine.
7. How many molecules of copper (I) sulfate are there in 7.25 grams of copper (I) sulfate?
8. How many moles in 3.89 x 1024 molecules of water?
9. How many atoms of nitrogen are there in 0.0254 grams of nitrogen?
10. How many aluminum atoms are there in 8.25 moles of aluminum oxide?
11. How many iron atoms are there in 3.45 moles of iron(III) chloride?
12. How many moles of copper (II) chloride could be made with 3.92 x 1023 atoms of
chlorine?
13. How many grams of ammonium phosphate are there in 4.67 x 1030 molecules of ammonium
phosphate?
14. How many atoms of oxygen are contained in a 4.89 moles of calcium hydroxide?
15. How many atoms of magnesium are in a 2.50 gram strip of magnesium?
More Mole Fun
1. What number of moles of zinc acetate contains 7.45 x 1022 molecules?
2. What number of sodium atoms is contained in 76.3 grams of sodium phosphate?
3. What mass of aluminum sulfide contains 7.4 x 1021 atoms of sulfur?
4. What is the mass of 7.65 moles of magnesium sulfate?
5. What number of moles of silver nitrate weighs 0.765 g?
6. What mass of lithium contains 8.9 x 1024 atoms of lithium?
7. Determine the number of total atoms in 65.0 g of glucose, C6H12O6.
8. What is the mass of 5.6 x 1024 molecules of carbon dioxide?
9. Determine the mass of tin (IV) chloride that can be made from 7.6 x 1020 atoms of
chlorine.
10. Determine the number of moles of barium acetate that contains 7.8 x 1019 atoms of
carbon?
More Mole Practice:
1 mole = 6.02 x 1023 atoms/molecules = molar mass (grams)
1. How many atoms are there in a 255 gram piece of copper metal?
2. What is the mass of 3.25 moles of sulfuric acid?
3. How many moles are present in 25.0 grams of iron (III) oxide?
4. How many grams of mercury (I) phosphate can be made from 9.6 x 1014 atoms of mercury
metal?
5. What mass of sodium chloride contains 4.59 x 1024 molecules?
6. How many molecules are contained in 4.35 x 10-2 moles of ZnCl2?
7. How many total atoms are contained in 3.2 x 1023 molecules of sodium sulfate?
8. How many moles are contained in 5.29 x 109 molecules of sodium sulfite?
9. How many atoms of oxygen are contained in 0.556 moles of aluminum acetate?
10. Determine the percent composition of each element in lead (IV) cyanide?
Answers:
1. 2.13 x 1024 atoms Cu
2. 319 g H2SO4
3. 0.157 moles Fe2O3
4. 3.7 x 10-7 grams Hg3PO4
5. 448 g NaCl
6. 2.62 x 1022 molecules ZnCl2
7. 2.2 x 1024 atoms
8. 8.79 x 10-15 moles Na2SO3
9. 2.01 x 1024 atoms O
10. Percent of Pb = 66.58%, Percent of C = 15.4%, Percent of N = 18.0%
NOTES:
% Composition, Empirical & Molecular formulas
C11 Honors
% Composition, Empirical & Molecular formulas
Answer the following problems. Be sure to show all work, include all units, and include all
significant figures.
1. A 25.00 gram sample of an oxide is found to contain 23.21 grams of lead,
and 1.79 grams of oxygen. What is the % composition of this compound?
2. Find the % composition of each element in the formula Mg3(AsO4)2.
3. What is the empirical formula for copper fluoride, which is 62.6% copper?
4. What is the empirical formula of a compound found to contain 111.16 grams of iron and
63.84 grams of sulfur?
5. Iron(III) chloride is 34.43% iron and 65.57% chlorine.
What mass of EACH ELEMENT can be obtained from a 60.0 gram sample?
6. The empirical formula of a compound containing phosphorus and oxygen was found to be
P2O5. Experiments show the molar mass of the compound to be 283.89 g. What is the
molecular formula of the compound?
7. An analysis of a gas reveals this composition: carbon 92.3% and hydrogen 7.7%.
Its molecular weight is 26.0 grams. What is the molecular formula?
8. A compound is composed of 7.20 grams of carbon, 1.20 grams of hydrogen, and 9.60 grams
of oxygen. The molar mass (molecular weight) of the compound is 60.0 grams. First find the
empirical formula and then the molecular formula for this compound.
9. Find the simplest formula for a compound that is 52.6% nickel, 21.9% carbon.
and 25.5% nitrogen. Write the name of this compound.
10. Find the % composition of a compound which is 10.12 grams of aluminum and 17.93 grams
of sulfur.
Honors Chem
Hydrates 2011
Name ____________
Hour ____________
1. A hydrate, A•?H2O, contains 3.5 moles A and 24.5 moles water. Determine the formula of
the hydrate.
2. A hydrate, B•?H2O, contains 0.00456 moles of B and 0.0228 moles of water. Determine
the formula of the hydrate.
3. A hydrate, D•?H2O, contains 0.560g of compound D, molecular weight of 46.0g, and
0.657 g of H2O. Determine the formula of the hydrate.
4. A hydrate of sodium acetate is found to contain 0.205g of anhydrous sodium acetate and
0.135g of H2O. Determine the formula of the hydrate.
5. A 0.7352 sample of hydrate of iron III phosphate decomposes to produce 0.4976g of
anhydrous iron III phosphate.
a. Determine the mass of water in this sample of hydrate.
b. Determine the formula of the hydrate.
6. The following data was collected when analyzing a hydrate of cobalt II chloride.
Mass of hydrate 1.427g
Mass of anhydrous salt 0.779g
Determine the formula of the hydrate.
7. The following data was collected when analyzing a hydrate of ammonium oxalate.
Mass of empty crucible
18.650g
Mass of crucible and hydrate
19.857g
Mass of crucible and anhydrous salt 19.704g
Formula of anhydrous salt __________
Determine the formula of the hydrate.
8. The following data was collected when analyzing a hydrate of manganese II chloride.
Mass of empty crucible
19.458g
Mass of crucible and hydrate
20.041g
Mass of crucible and anhydrous salt 19.911g
Formula of anhydrous salt __________
Determine the formula of the hydrate.
Chapter 11 Mole Test Review
1. What number of moles of phosphorus is 456.76 grams of phosphorus?
2. What is the empirical formula of a substance that contains 31.9% potassium, 29%
chlorine, and 39.1% oxygen?
3. What is the percent composition of EACH ELEMENT in magnesium phosphate?
4. A student determines that a hydrate of copper (II) sulfate contains 38.30 grams of
anhydrous copper (II) sulfate and 25.92 grams of water. What is the formula of the
hydrate?
5. What number of atoms of oxygen are contained in 34.56 grams of calcium hydroxide?
6. What is the empirical formula of a compound that contains 3.90 grams of iron and 1.68
grams of oxygen?
7. What is the molecular formula of a compound that has a molecular weight of 472.2 grams
and is 85% mercury and 15% chlorine?
8. What has a greater percentage of iron; Fe2O3 or FeO? Explain.
9. How many molecules of aluminum oxide are in 65.4 grams?
10. How many moles of magnesium nitride can be made from 7.08 x 1012 atoms of nitrogen?
11. How many atoms of lithium are in 65.8 grams of lithium?
Answers to Calculations:
Molar Mass/Molecular Weight:
1. 55.8 g/mol
11. 95.3 g/mol, 25.5% Mg
2. 52.0 g/mol
12. 216.6 g/mol, 92.61% Hg
3. 71.0 g/mol
13. 342.3 g/mol, 15.8% Al
4. 18.0 g/mol, 11% H
14. 342.0 g/mol, 42.11% C
5. 60.1 g/mol, 46.8% Si
15. 190.4 g/mol, 33.4% Cu
6. 98.0 g/mol, 3.1% H
16. 131.3 g/mol, 89.34% K
7. 151.9 g/mol, 36.7% Fe 17. 284.0 g/mol, 43.66% P
8. 149.0 g/mol, 28.2% N 18. 177.8 g/mol, 66.25% Co
9. 187.5 g/mol, 33.9% Cu 19. 156.3 g/mol, 25.7% Ca
10. 60.0 g/mol, 40.0% C
20. 152.7 g/mol, 77.73% Sn
Mole Fun:
1. 5.1 grams
2. 46.3 grams
3. 6.78 x 1022 molecules
4. 1.54 x 109 moles
5. 703 grams
6. 2.33 grams
7. 1.96 x 1022 molecules
8. 6.46 moles
9. 1.09 x 1021 atoms
10. 9.93 x 1024 atoms
More Mole Fun:
1. 0.124 moles
2. 8.40 x 1023 atoms
3. 0.62 grams
4. 921 grams
5. 0.00450 moles
6. 100 grams
7. 5.21 x 1024 atoms
8. 410 grams
9. 0.082 grams
10. 3.2 x 10-5 moles
11.
12.
13.
14.
15.
24
2.08 x 10 atoms
0.326 moles
1.16 x 109 grams
5.89 x 1024 atoms
6.19 x 1022 atoms
% Comp,Emp.&Molec.Formulas:
1. 92.84% Pb, 7.16% O
2. 20.8% Mg, 42.7% As, 36.5% O
3. CuF2
4. FeS
5. 20.7 g Fe, 39.3 g Cl
6. P4O10
7. C2H2
8. Emp: CH2O, Molec: C2H4O2
9. Ni(CN)2, nickel (II) cyanide
10. 36.08% Al, 63.92% S
Hydrates:
1. A 7H2O
2. B 5H2O
3. D 3H2O
4. NaC2H3O2 3H2O
5. 0.2376 g, FePO4 4H2O
6. CoCl2 6H2O
7. (NH4)2C2O4 H2O
8. MnCl2 2H2O
Review:
1. 3.684 moles
16. 2.5 x 10-8 moles
2. KClO3
17. 3.6 x 1024 atoms
3. 27.7% Mg, 23.6% P, 48.7% O
4. CuSO4 6H2O
18. Na2S2O3
23
5. 5.62 x 10 atoms
19. Ba(OH)2 8H2O
6. Fe2O3
20. 4.9 x 1021 atoms
7. Hg2Cl2
8. Fe2O3: 69.9% Fe, FeO: 77.7% Fe
9. 3.86 x 1023 molecules
10. 5.88 x 10-12 moles
11. 5.7 x 1024 atoms
12. 1.50 x 1024 atoms
13. 53.83% C, 6.41% H, 8.97% N, 10.3% S, 20.5% O
14. Emp: P2O5, Molec: P4O10
15. 0.0840 grams