Chemistry Moles Packet, Lecture notes of Chemistry

Download Chemistry Moles Packet and more Lecture notes Chemistry in PDF only on Docsity!

Chemistry

Moles Packet

INTRODUCTION TO MOLES

We are about to start on a unit of chemical calculations called “stoichiometry”. Stoichiometry is how we calculate the relationships between the amounts of reactants and the amounts of products. For example, if we know the amount of reactants we have, we can use stoichiometry to calculate how many products the chemical reaction will produce.

This packet provides an organized, step-by-step approach for these problems. If you follow this system and complete work each day as it is assigned, this will not be a difficult unit. That is good, because stoichiometry is one of the most central and important concepts in chemistry. It is essential that you understand this unit in order to move forward in chemistry. In short: do not fall behind or you will be lost.

These problems involve numbers but no difficult mathematics. All you will ever have to do is add, multiply or divide. You will be expected to have a functioning calculator with you for every chemistry class. As we solve these problems we will apply the factor-label (dimensional analysis) method you mastered early in the class, and we will frequently use scientific notation. Remember chapter 3 you followed the procedure:

what you are = what you are X a fraction or series of fractions where the = looking for given numerator is equivalent to the denominator

The only new concept we will introduce in this unit is the idea of a mole. A mole is a quantity of matter that we use for conversion purposes. We can convert from grams to moles, liters to moles (for gases), and atoms or molecules to moles. If you can convert any of these things to moles (and therefore moles to any of these things) we can convert grams to liters or molecules, liters to grams of molecules, and molecules to liters or grams.

answer

Molar Mass (# grams) Atomic Weight (for elements) or Gram Formula/Molecular Weight (for compounds)

6.02 X 10^23 ATOMS (for elements) or 6.02 X 10^23 MOLECULES ( for compounds)

MOLES

22.4 LITERS OF A GAS AT STP (standard temperature and pressure)

FORMULA CALCULATION MASS OF A MOLE

1. calcium phosphate _______________ ________________
2. sodium carbonate _______________ ________________
3. ammonia _______________ ________________
4. potassium chlorate _______________ ________________
5. lead(II) nitrate _______________ ________________
6. sodium oxalate _______________ ________________
7. zinc chloride _______________ ________________
8. magnesium oxide _______________ ________________
9. antimony(III) chloride _______________ ________________
10. nitrogen _______________ ________________
11. oxygen _______________ ________________
12. fluorine _______________ ________________
13. chlorine _______________ ________________

CHEMISTRY WORKSHEET # 2: THE MOLE AS A UNIT OF MASS

Define the term molar mass (worksheet #1): _______________________________________________________ Now that you know how to find the mass of one mole of a substance (molar mass) you can easily find the mass of several moles or the mass of a fraction of a mole using the factor-label technique.

EXAMPLE: What is the mass of 5.00 moles of water(H 2 0)? 2 H = 2 x( 1.01) = 2.02 # grams H 2 0 = 5.00 moles H 2 0 x 18.02 g H 2 0 = 90.10 g H 2 O O = 1 x(16.00) = 16.00 1 mole H 20

H 2 0 = 18.02 g

NOW YOU TRY ONE: What is the mass of 0.50 moles of calcium carbonate(CaCO 3 )? Ca = #g CaCO 3 = C = 3O =

CaCO 3 =

USE A SEPARATE SHEET OF PAPER TO SOLVE THE FOLLOWING PROBLEMS. SHOW YOUR WORK. ROUND MOLAR MASSES TO TWO PLACES AFTER THE DECIMAL. ADD UNITS.

1. How many grams are there in 5.00 moles of lead?
2. How many grams are there in 2.00 moles of sulfuric acid?
3. How many grams are there in 0.250 moles of sodium hydroxide?
4. How many grams are there in 2.50 moles of potassium nitrate?
5. How many grams are there in 10.0 moles of lithium carbonate?

Now that you know how to find the mass of one mole of a substance you can easily find the number of moles there are in a given mass of the substance.

EXAMPLE: How many moles of calcium chloride are there in 333 grams of calcium chloride (CaCl 2 )?

Ca = 1 x(40.08)= 40.08 # moles CaCl 2 = 333 grams CaCl 2 x 1 mole CaCl 2 = 3.00 mole CaCl 2 2 Cl = 2 x(35.45)= 70.90 110.98 g CaCl 2 CaCl 2 = 110.98 g

USE THE SAME PAPER AS THE ABOVE PROBLEMS TO SOLVE THE FOLLOWING. SHOW YOUR WORK AND PUT UNITS ON EACH ANSWER!

1. How many moles of silver nitrate are there in 80.00 grams of silver nitrate?
2. How many moles of phosphoric acid are there in 658 grams of phosphoric acid?
3. How many moles of tin (II) fluoride are there in 908 grams of tin (II) fluoride?
4. How many moles of hydrogen peroxide (H 2 O 2 ) are there in 1000.0 grams of hydrogen peroxide?
5. How many moles of magnesium chloride are there in 148 grams of magnesium chloride?

#1-5: You are given the number of moles and asked to find the grams (mass)

MOLS  GRAMS

#6-10: You are given the grams (mass) and asked to find the number of mols

GRAMS  MOLS

CHEMISTRY WORKSHEET # 4 MOLAR MASSES AND AVOGADRO’S NUMBER

Now that you know two definitions of a mole (a gram formula weight and an Avogadro’s number of particles) you can combine these two definitions into one problem.

EXAMPLE: How many molecules are there in 90.1 grams of water?

2 H = 2 x(1.01) = 2. O = 1 x (16.00) = 16. H 2 O = 18.02 g

molecules H 2 O = 90.1 g H 2 O x 1 mole H 2 O x 6.02 x 10^23 molecules H 2 O = 3.01 x 10^24 molecules H 2 O

18.02 g H 2 O 1 mole H 2 O

EXAMPLE: What would be the mass of 3.01 x 10^23 molecules of ammonia (NH 3 )?

N = 1 x (14.01) = 14. 3 H = 3 x (1.01) = 3. NH 3 = 17.04 g

grams NH 3 = 3.01 x 10^23 molecules NH 3 x 1 mole NH 3 x 17.04 g NH 3 = 8.52 g NH 3

6.02 x 10^23 molecules NH 3 1 mole NH 3

SOLVE THE FOLLOWING PROBLEMS ON A SEPARATE SHEET OF PAPER. YOU MUST SHOW

ALL OF THE STEPS AND YOU MUST DO THE PROBLEM JUST AS ILLUSTRATED. INCLUDE UNITS!

1. How many molecules are there in 345 grams of carbon dioxide?
2. What would be the mass, in grams, of 1.204 x 10^24 molecules of sulfur dioxide?
3. How many molecules of sucrose, C 12 H 22 O 11 , are there in 454 grams of sucrose?
4. What would be the mass, in grams, of 1.806 x 10^24 molecules of carbon monoxide?
5. How many molecules of water are there in 8.050 x 10^3 grams of water?
6. How many oxygen molecules are in a flask that contains 1.43 grams of oxygen?
7. What would be the mass, in grams, of 1.505 x 10^23 molecules of carbon disulfide?
8. How many molecules of hydrogen chloride would there be in 100.00 grams of this gas?
9. What would be the mass, in grams, of 2.408 x 10^24 molecules of tetraphosphorus decaoxide?

Extra Challenge:

1. How many hydrogen molecules are there in 1 ton of hydrogen? (Hint: How many grams are there in 1 ton?)

CHEMISTRY WORKSHEET # 5 MOLE PROBLEMS—MOLAR VOLUME OF A GAS

We have learned that a mole is a mass of material and number of particles. A mole can also be a measure of volume when we are talking about gases. You may remember from previous science classes that all gases behave basically the same as far as the physical properties of temperature, pressure and volume. AVOGADRO’S HYPOTHESIS SAYS THAT EQUAL VOLUMES OF GASES AT THE SAME TEMPERATURE AND PRESSURE CONTAIN EQUAL NUMBERS OF MOLECULES. Avogadro’s statement makes sense and is possible because gases are mainly empty space—only about one thousandth of the space is actually filled with molecules. The molecules “fill” the remaining space by moving rapidly through it. So the difference in size between large molecules and small molecules is insignificant compared to the total volume the gas occupies. At standard temperature and presssure (STP = OoCelcius and 1.00 atm pressure) one mole of any gas will have a volume of 22.4 liters. In other words, THE MOLAR VOLUME OF ANY GAS IS 22.4 LITERS AT STP. Once we know this we can convert from moles to liters or liters to moles for any gas at STP.

EXAMPLE: What is the volume, in liters, of a 2.00 mole sample of methane (CH 4 ) at STP?

L CH 4 = 2.00 moles CH 4 x 22.4 L CH 4 = 44.80 L CH 4

1 mole CH 4

EXAMPLE: How many moles of ethane (C 2 H 6 ) are there in 5.60 liters of ethane?

moles C 2 H 6 = 5.60 L C 2 H 6 x 1 mole C 2 H 6 = 0.25 mole C 2 H 6

22.4 L C 2 H 6

COMPLETE THE FOLLOWING PROBLEMS ON A SEPARATE SHEET OF PAPER USING THE

SAME SET-UP AS SHOWN ABOVE. WRITE THE FORMULAS FOR THE COMPOUNDS, NOT JUST THE

NAMES. INCLUDE UNITS!

1. What is the volume, in liters, of 2.00 moles of hydrogen at STP?
2. How many liters will 5.00 moles of oxygen occupy at STP?
3. What is the volume, in liters, of 0.250 moles of carbon monoxide at STP?
4. What is the volume, in liters, of a 3.00 mole sample of carbon dioxide at STP?
5. How many moles of chlorine are there in a 67.2 liter sample of chlorine at STP?
6. A 44.8 liter sample of nitrogen at STP will contain how many moles of nitrogen?
7. How many moles of ammonia are there in 405 liters of ammonia at STP?
8. How many moles of neon would you need to fill a 33.6 liter container at STP?
9. How many moles of argon are there in 5.00 x 10^2 liters of argon at STP?
10. What is the volume, in liters, of 4.50 moles of fluorine at STP?

Extra Challenge

1. How many moles of nitrogen are there in a 16,500 mL sample of nitrogen at STP?

10 CHEMISTRY WORKSHEET # 7: GENERAL REVIEW OF MOLE PROBLEMS

Now we have studied the idea of moles and learned three interpretations of a mole: (1) A gram formula weight. (2) An Avogadro’s number of particles. (3) 22.4 liters of gas at STP.

Solve the following problems involving the mole concept. (If you are having difficulty go back and review mole worksheets 1-6.)

Problems 1-2: moles to grams AND grams to moles

1. How many grams are there in 11.8 moles of sodium hydroxide? Ans. 472 grams sodium hydroxide
2. How many moles are there in 215 grams of water? Ans. 11.9 moles water

Problems 3-4: moles to molecules AND molecules to moles

1. How many molecules are there in 3.85 moles of carbon tetrachloride? Ans. 2.32 x 10^24 molecules carbon tetrachloride
2. How many moles are there in 8.25 x 10^26 molecules of methane? Ans. 1.37 x 10^3 moles of methane

Problems 5-6: grams to moles to molecules AND molecules to moles to grams

1. How many molecules are there in 295 grams of ammonia? Ans. 1.04 x 10^25 molecules of ammonia
2. How many grams are there in 8.95 x 10^26 molecules of carbon disulfide? Ans. 1.13 x 10^5 grams of carbon disulfide

MOLAR MASS (G/MOL)

MOLE

22.4 LITERS OF GAS AT STP

6.02 X 10^23 PARTICLES (ATOMS OR MOLECULES)

11

Problems 7-8: moles to liters AND liters to moles

1. What would be the volume, in liters measured at STP, of 9.75 moles of carbon monoxide? Ans. 2.18 x 10^2 liters of carbon monoxide
2. How many moles would there be in 5.25 liters of oxygen measured at STP? Ans. 0.234 moles or 2.34 x 10-1^ moles oxygen

Problems 9-10: grams to moles to liters AND liters to moles to grams

1. What is the volume, measured in liters at STP, of 285 grams of the gas acetylene, C 2 H 2? Ans. 245 liters of acetylene
2. How many grams are there in 512 liters (measured at STP) of propane, C 3 H 8? Ans. 1.01 x 10^3 grams of propane

Problems 11-12: molecules to moles to liters AND liters to moles to molecules

1. What would the volume be, measured in liters at STP, of 3.01 x 10^25 molecules of fluorine? Ans. 1.12 x 10^3 liters of fluorine
2. How many molecules are there in 995 liters of sulfur dioxide at STP? Ans. 2.67 x 10^25 molecules of sulfur dioxide

Problems 13-16: Mixed Problems- Think about what type of conversion you are doing!

1. How many molecules are there in 2270 g of table sugar, sucrose. Ans. 3.99 x 10^24 molecules of sucrose
2. How many molecules would there be in 1.135 x 10^6 g of chlorine? Ans. 9.64 x 10^27 molecules of chlorine
3. What would the mass be, in grams, of 348 liters of carbon dioxide measured at STP? Ans. 684 grams of carbon dioxide
4. How many molecules of nitrogen are there in 200 L of nitrogen measured at STP?