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Unit 9: Chapter 10
Chemical Quantities
Page 1
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Block:
Unit 9 Worksheet 1- Section 10.1: Converting between moles and particles. Calculating molar mass.
1.
Which of the following conversion factors is properly written?
a. 6.022 x 1023 moles NaCl
2.
3.
b. 6.022 x1023 f.u. NaCl
1 f.u. NaCl
1 mol NaCl
What are the 4 types of representative particles?
c. 6.022 x 1023 ions Na+ and Cl-
1 mol NaCl
How can you tell which type of representative particle a substance is?
For each of the following conversions, first indicate whether you will need 1 or 2 conversions. To figure this out, examine the representative
particles. Then SHOW WORK for the conversion. Please include units throughout. Enclose your answer in a box or highlight answer.
Convert from… to….
1 or 2 conversion
WORK AND ANSWER
factors?
4) 8.2 moles of NaCl
to formula units of
NaCl
5) 7.6 moles of NaCl
to ions of Na+
3) 3.4 moles of NaCl
to total ions (Na+ and
Cl-)
4) 5.6 x 1034
molecules of O2 into
moles of O2
5) 7.8 x 1056 atoms of
O into moles of O2
6) 9.8 x 1058
molecules of H2O into
moles of H2O
7) How many ions of
sodium are in 2 moles
of sodium chloride?
(hint: write the
formula first)
8) How many formula
units are in 7 moles
of potassium iodide?
9) How many moles of
hydrogen (H2) are
present if you have
8.9 x 1078 molecules
of hydrogen (H2) ?
10) How many moles of
hydrogen (H2) are
present if you have
8.9 x 1078 ATOMS of
hydrogen (H)?
For each of the following, find the molar mass. SHOW YOUR WORK. INCLUDE CORRECT UNITS.
Enclose your answer in a box or highlight answer.
11) H2SO4
12) KI
13) H2S
14) H2
15) O2
Unit 9: Chapter 10
Name:
Chemical Quantities
Page 2
Block:
Unit 9 Worksheet 2- Section 10.2 Molar Mass & Molar Volume Conversions (there are 19 questions total)
1. Does 1 mole of a solid, 1 mole of a liquid, or 1 mole of a gas have the same volume?
2. Under what conditions is your answer to #1 true?
3. Why is this not true if the temperature is higher?
4. Why is this not true if the temperature is lower?
5. Why is this not true if the pressure changes?
6. Would 3 balloons with the same number of molecules of different gases at STP have the same mass or
the same volume? Explain.
7. The densities of gases A, B, and C are 1.25 g/L, 2.86 g/L, and 0.714 g/L respectively. Calculate the
molar mass of each substance. Identify each substance as ammonia (NH3), sulfur dioxide (SO2),
chlorine (Cl2), nitrogen (N2), or methane (CH4). (show your work please)
Remember which atoms are diatomic. Some problems will require more than one conversion.
Convert from… to….
Which are you going to
use: avogadro’s #, Molar
Mass, Molar Volume at
STP? If you are going to
use molar mass, write the
value of the molar mass.
WORK AND ANSWER- please show your work. All numbers must have proper
units, answers should be highlighted or enclosed in a box.
8) 8.76 moles of NaCl to grams
9) 87.6 grams of KCl to moles of KCl
10) 44.8 L of nitrogen gas at STP to
moles of nitrogen gas
11) 1.2 moles of nitrogen gas to liters
of nitrogen gas at STP
12) 44.8 L of oxygen gas to grams of
oxygen gas at STP
13) 87.5 grams of H2O to molecules of
H2O
14) 67.5 grams of oxygen gas to atoms
of oxygen (remember oxygen is
diatomic)
15) 3.45 x 1056 atoms of nitrogen to
grams of nitrogen gas (N2)
16) 98 grams of KNO3 to formula units
of KNO3
17) What is the density of Ar gas at
STP?
18) (review from a past unit) Which of the above compounds are ionic? (list them all please)
19) Which of the above compounds are covalent? (list them all please)
Unit 9: Chapter 10
Name:
Chemical Quantities
Page 3
Block:
Unit 9 - Worksheet 3: Section 10.3- Percent Composition, Empirical Formula, Molecular Formula (there
are 16 questions)
For each of the following, calculate the percentage composition. Please show your work!!! I will give credit
only to those who show their work. You must use your own paper! Hint: for questions 6-9 you will need to write
the formula first.
1) NaCl
2) (NH4)2Cr2O7
3) potassium nitrate
4) phosphoric acid
5) How many atoms of hydrogen can be obtained from 35 grams of water?
6) How many moles of hydrogen atoms can be obtained from 35 grams of water?
7) Can 18 grams of oxygen be obtained by heating 50.0 grams of potassium chlorate?
For each of the following, determine the empirical formula. Only problems with the work shown will receive
credit. You must use your own paper
8) 42.50% chromium; 57.50% chlorine
9) 75.0% carbon, 25.0% hydrogen
10) A sample of potassium sulfate has the following composition: 17.96 g of potassium, 7.35 g of sulfur,
14.70 g of oxygen. What is its simplest formula.
11) 11.0 g of a certain compound contain 2.82 g of magnesium and 8.18 g of chlorine. What is its empirical
formula?
12) Write the empirical formula for C6H12O6.
For each of the following, determine the molecular formula. Only problems with the work shown will receive
credit. You must use your own paper.
13) A compound has an empirical formula of ClCH2 and a molecular weight (molar mass) of 98.96 g/mol.
What is its molecular formula?
14) A compound contains 18.8% sodium, 29.0% chlorine, and 52.2% oxygen, by mass. If the molar mass of
the compound is 122.44 g/mol, determine the empirical and molecular formulas.
15) A 4.99 gram sample of a compound contains 1.52 grams of nitrogen atoms and 3.47 grams of oxygen
atoms. The molar mass of the compound is 92.04g. Determine the empirical and molecular formulas.
16) For each of the following, list whether the formula is empirical or molecular: (some formulas may be
both empirical and molecular, in this case, just write empirical)
a. CH2O
b. C6H12O6
c. CH4
d. C2H8
17) BONUS: 0.916 g of iron is heated in air. The resulting product has a mass of 1.178g. (oxygen in the air
reacts with iron to form this compound and no iron is left over) what is the empirical formula of the
compound?
18) BONUS 27.3% carbon; 72.7% oxygen, 1.0 dm3 has a mass of 1.96 g (assume the compound is a gas at
STP) What is the molecular formula?
19) BONUS: 85.72% carbon; 14.28% hydrogen; 2.0 L have a mass of 2.50 g (assume the compound is a
gas at STP) What is the molecular formula?
20) BONUS: 10.04% carbon; 0.84% hydrogen, 89.12% chlorine; 1.0 dm3 has a mass of 5.30 g. What is the
molecular formula?
Unit 9: Chapter 10
Name:
Chemical Quantities
Page 4
Block:
Empirical Formula Determination
Background: When you burn something you are combining it with oxygen. When magnesium is burned, it
combines with oxygen from the air to form a solid MgxOy. The mass of the magnesium then should
when you burn it because it is combining with oxygen from the air. (in the blank, fill in
increase or decrease)
Objective: to determine the empirical formula of the compound formed by magnesium and oxygen when
magnesium is burned. (in other words, to fill in the values for x and y in the formula from the background
information.
Reagents: Magnesium and oxygen. Our reaction is: 2 Mg (s) + O2(g)  2MgO (s)
Equipment: ring stand, ring clamp, clay triangle, metal crucible, crucible tongs, metal crucible lid, Bunsen
burner, scale
Procedure: you must write your own procedure. Please remember that it must be numbered vertically.
Please write commands, not a narrative of what you did. It should be written in formal language. You do
not need to say “we did….” Please avoid the use of abbreviations as well. Think about the information you
need to find empirical formula. How will you find that information?
Helpful hints for your procedure:

Touching the crucible will add finger oil and result in inaccurate readings for the mass.
You will want to burn off any oils before you start the experiment!

You cannot look directly at the magnesium as it burns, so covering it would be a good idea

You cannot measure the mass of the crucible when it is hot

You will know that magnesium has fully reacted with the oxygen in the air when it
becomes gray and crumbly.
Results: You must include either a data table or a well organized and well labeled list with all the data you
collected during your experiment.
Answer the following questions under your results section.
1) How many grams of oxygen were present? SHOW YOUR WORK
2) Convert from grams of magnesium to moles of magnesium. SHOW YOUR WORK
3) Convert from grams of oxygen to moles of oxygen. SHOW YOUR WORK
4) Determine the empirical formula for magnesium oxide BASED ON YOUR DATA and
calculations from the questions above. SHOW YOUR WORK.
5) Using your knowledge regarding ionic formulas, what SHOULD the empirical formula for
magnesium oxide be? (if needed, look back to unit 4)
6) Determine your % error for moles of magnesium in your empirical formula based on your
answers to questions 4 and 5.
7) Determine your % error for moles of oxygen in your empirical formula based on your
answers to questions 4 and 5.
Conclusion:
Don’t forget to write your conclusion. Remember that you need a summary that relates back to the
objective. Please write your conclusion using full sentences with proper grammar. The conclusion should
be in a paragraph form that stands on its own. I have provided a list of questions to help guide you.
However, the reader should not need to read the questions to understand your conclusion. Remember that
the summary does not need all of the detail present in the procedure when you are describing what you did.
You can be more general in the conclusion. List of questions to help guide you: How did you meet your
objective? What was your main result? Where were there potential errors? How did you avoid these
errors? OR How would you avoid the errors next time? You may want to consider the scale. Did you use
the same one each time? Does it matter if you did? Could you tell if the reaction was complete? How?
Unit 9: Chapter 10
Chemical Quantities
Page 5
Name:
Block:
Unit 9 Study Guide (U9SG)- you must write on your own paper (There are 28 Questions)
Remember to study your goals and terms for each section. Look over your worksheets and in class
practice problems. If you need additional conversion practice, there are extra practice problems on the
in class practice sheet.
1. What are the 7 diatomic molecules?
2. Can the molecular formula be the same as the empirical formula?
3. Can compounds have the same empirical formula but different molecular formulas?
4. When using molar volume, why is it important that the gas be at STP?
5. Which of the following are equal to Avogadro’s number? (Circle or list all that apply): The number of
atoms in 1 mole of Br2, The number of atoms in 1 mole of Au, the number of molecules in 1 mole of Cl2,
the number of molecules in 1 mole of CO2.
6. Which of the following compounds have the same empirical formula: CH4, C2H6, C2H8, C2H2?
7. If the density of an unknown gas Z is 4.50 g/L at STP, what is the molar mass of gas Z?
a.
0.201 g/mol c.
26.9 g/mol
b.
5.00 g/mol
d.
101 g/mol
8. What is the density at STP of the gas sulfur hexafluoride, SF ?
a.
0.153 g/L
c.
3270 g/L
b.
6.52 g/L
d.
d.
3.93 1024 g/L
FOR ALL OF THE REMAINING QUESTIONS, YOU MUST SHOW YOUR WORK FOR
CREDIT!!!
9. What is the molar mass of AuCl3?
10. What is the molar mass of bromine gas?
11. What is the percent by mass of hydrogen in aspirin, C H O ?
12. Calculate the molecular formula of the compound with the following empirical formula and molar
mass: C H , 58 g/mol.
13. How many moles of silver atoms are in 1.8 1020 atoms of silver?
14. What is the empirical formula of a compound that is 40% sulfur and 60% oxygen by weight?
15. Find the mass in grams of 8.7 1023 molecules of fluorine gas.
16. Find the number of moles of argon in 67 g of argon.
17. Find the mass, in grams, of 9.40 1023 atoms of Br.
18. What is the percent composition of MgO if the mass of Mg is 48.62 g and the mass of O is 32.00 g?
19. How many moles of tungsten atoms are in 8 1025 atoms of tungsten?
20. What is the mass of silver in 9.45 g AgNO ?
21. How many carbon atoms are in 5 molecules of isopropyl alcohol, C H O?
22. What is the number of moles in 87 L of H S gas at STP?
23. What is the volume, in liters, of 9.500 mol of C H gas at STP?
24. What is the mass in grams of 760 mol C H ?
25. What is the molar mass of Fe2(SO4)3 ?
26. How many atoms are in 9.5 moles of arsenic atoms?
27. How many molecules are in 7.10 mol CO ?
28. How many atoms of chlorine are present in 98.5 L of Chlorine gas (Cl2)?