Homework: Mass to Moles Calculations
*
Convert the following mass amounts into mole amounts. Remember, you first need to calculate the molar mass
of the compound. Then, use this quantity as a conversion factor.
1. A box contains 250 grams of NaHCO3 (baking soda). How many moles of baking soda are in the box?
2. You used 300 grams of Na2CO3 (laundry detergent) to wash one load of laundry. How many moles of
laundry detergent did you use?
3. A jar contains 750 grams of MgSO4 (Epsom salts). How many moles of Epsom salts are in the jar?
4. A container of Na3PO4 (sodium phosphate) sold at the hardware store contains 500 grams of the powder.
How many moles of sodium phosphate are in the container?
5. A plant gives off 10 grams of (CO2) carbon dioxide per minute. How many moles of carbon dioxide is
this?
Homework: Moles to Mass Calculations
Convert the following mass amounts into mole amounts. Remember, you first need to calculate the molar mass
of the compound. Then, use this quantity as a conversion factor.
1. How many grams of potassium hydrogen tartrate, KHC4H4O6, are in 0.100 moles of the solid?
2. How many grams of water are in 55.56 moles of the liquid?
3. How many grams of tin(II) fluoride (SnF2) are in 0.025 moles of the substance?
4. How many grams of chalk (CaCO3) are in a piece containing 0.654 moles?
5. How many grams of glucose (C6H12O6) are produced in 1.25 moles?
Mini-Labs: Moles of…
Objective: To practice conversions between grams, moles, and molecules
To allow for visualization of quantities of moles and molecules
I. Moles of Dihydrogen Monoxide (AKA…water):
1. Place an empty beaker on the balance.
2. Push the “Tare” button on the balance to zero it.
3. Pour any amount of water into your beaker and record this mass of water in your data table below.
4. Looking at the quantity of water in your beaker, estimate quantities of moles and molecules. Write your
estimates on the lines below. There are not right or wrong answers to these questions. Just randomly
pick some numbers.
* How many moles of H2O do you think are in your beaker? _____________________
* How many molecules of H2O do you think are in your beaker? __________________
5. Calculate the molar mass of H2O. Show your work for this calculation below and record this final
answer in the data table below.
6. Use the conversion factor method to calculate the exact number of moles of H2O in your beaker. Show
your work for this calculation below and write your final answer in the data table below.
7. Use the conversion factor method to calculate the exact number of H2O molecules that are in your
beaker. Show your work for this calculation below and write your final answer in the data table below.
SHOW ALL WORK HERE:
ENTER ALL FINAL ANSWERS INTO THE DATA TABLE BELOW
(remember to label each number with a unit):
Mass in grams of the H2O in the beaker =
Molar Mass of H2O =
Moles of H2O in the beaker =
Molecules of H2O in the beaker =
II. Moles of Sucrose (C12H22O11) in Bubble Gum:
1. Get one piece of bubble gum. Do not throw away the wrapper!!
2. Put the gum wrapper onto the balance and push the “Tare” button to zero the balance. Put the unchewed
piece of gum onto the paper. Record the mass of your unchewed gum in the data table below.
3. Chew the bubble gum until you do not taste any more flavor.
4. Put your gum wrapper onto the balance and push the “Tare” button to zero the balance. Then, put your
chewed gum onto the paper. Record the mass of your chewed gum in the data table below.
5. Using the mass of the chewed gum and the unchewed gum, calculate the mass of sucrose (or sugar) in
your piece of bubble gum. Show your work for this calculation in the space below and record your final
answer in the data table.
6. Looking at the mass of sucrose in your gum, estimate quantities of moles and molecules. Write your
estimates on the lines below. There are not right or wrong answers.
* How many moles of sucrose do you think are in your gum? _____________________
* How many molecules of sucrose do you think are in your gum? _________________
7. Calculate the molar mass of sucrose (C12H22O11). Show your work for this calculation in the space
below and record your final answer in the data table.
8. Use the conversion factor method to calculate the exact number of moles of sucrose in your gum. Show
your work for this calculation below and write your final answer in the data table below.
9. Use the conversion factor method to calculate the exact number of sucrose molecules that are in your
gum. Show your work for this calculation below and write your final answer in the data table below.
SHOW ALL WORK HERE:
ENTER ALL FINAL ANSWERS INTO THE DATA TABLE BELOW
(remember to label each number with a unit):
Mass in grams of unchewed gum =
Mass in grams of chewed gum =
Mass of sucrose (sugar) in the gum =
Molar mass of sucrose (C12H22O11) =
Moles of (C12H22O11) in your gum =
Molecules of (C12H22O11) in your gum
=
Applied Chemistry
Today…
1. Complete the “Review Calculations” below. You must show all work for each calculation! You
may use your notes and previous homework assignments to complete these problems. This must
be done independently!
2. Copy the example calculations off of the board and into your Unit 4 packet: “B. Moles to Mass
Calculations”.
3. Work on/complete the homework handout associated with these new notes. These homework
problems are exactly like the sample calculations. Use your notes to complete the homework. All
problems must be attempted for 5 points credit tomorrow.
Review Calculations:
1. What is the molar mass of the compound Ba(NO3)2?
2. What is the percent composition of all elements in the compound AlCl3?
3. Potassium and sulfur are combined experimentally to make potassium sulfide, K2S. If 3.75 grams of
potassium (K) are used to produce 5.30 g of the compound, what is the percent composition by mass of
potassium in the compound?
What is the percent composition by mass of sulfur in the final compound?
4. How many moles of hydrogen peroxide (H2O2) are in a bottle containing 25 g of the compound?
Unit 4: The Mole
I. Introduction: Since atoms, molecules, and ions are extremely small particles, it is not practical to talk about 1, 2, or
3 of these particles reacting or being produced in a chemical reaction. In fact, it may not be possible to see evidence
of 1, 2, or 3 million of these particles. Because of this, the concept of the mole is used in chemistry.
Definition of a Mole:
Definition of Avogadro’s Number:
Question…What does a mole of carbon represent?
Question…What does a mole of hydrogen represent?
Summary: A mole of any substance always contains 6.02 x 1023 particles, but the mass of a mole will vary
depending upon the substance.
II. Molar Mass: Molar mass takes into account the atomic mass from the periodic table. It is the small, red number in
the upper right corner of your table.
Definition of Molar Mass:
How do we determine molar mass?
For elements…
For compounds…
Examples:
III. Percent Composition: Elements of a compound always combine in a constant proportion by mass. This is called the
Law of Definite Proportions.
Definition of Percent Compostion:
Formula for Percent Composition:
**Percent composition can be calculated in two ways. You must be able to solve both types of problems. Both use
the same formula, but are dependent upon different information.
1. Quantitative Analysis – based upon experimental data
Example:
When magnesium (Mg) burns, it combines with oxygen (O2) to form magnesium oxide (MgO). If 0.250 g of
magnesium are burned, 0.415 g of magnesium oxide form. Calculate the experimental percent composition of
magnesium in this compound.
2. Using Molar Mass Calculations – based upon mass information from the periodic table
Example:
What is the percent composition by mass of the elements in magnesium sulfate (MgSO4)?
IV. Conversion Factor Calculations: Moles, molar mass, and Avogadro’s number are used in calculations to predict
experimental yields. This information is set up in conversion factor format.
A. Mass to Moles Conversions:
Examples:
750 grams of sodium chloride (NaCl) are produced in a chemical reaction. How many moles of NaCl is this?
How many moles of water are in a glass containing 65 g of the liquid?
B. Moles to Mass Conversions:
Examples:
If 0.25 moles of potassium chloride (KCl) are needed for a reaction, how many grams of the compound must be
used?
How many grams of carbon dioxide (CO2) are produced from a reaction that makes 2.25 moles of the compound?
C. Moles to Particles (atoms or molecules) Conversions:
Examples:
How many carbon atoms are in 3.45 moles of the element?
D. Particles (atoms or molecules) to Moles Conversions:
Examples:
7.25 x 1023 atoms represent how many moles of nickel?
E. Mass to Particles (atoms or molecules) Conversions:
Examples:
If a reaction involves 3.5 grams of sodium, how many atoms of sodium will be reacting?
A reaction produced 7.25 grams of water (H2O). How many water molecules were produced?
F. Particles (atoms or molecules) to Mass Conversions:
Examples:
If 8.15 x 1023 potassium atoms are needed for a reaction, how many grams of the metal are needed?
A reaction requires 2.10 x 1024 molecules of table salt (NaCl). How many grams of the salt must be used?
V. Molarity (Concentration of Solutions): Solutions are homogeneous mixtures made when a solid dissolves
completely in a liquid. The ratio of solid to liquid results in the concentration of the solution, also known as molarity.
Definition of Molarity:
Formulas for Molarity calculations:
Examples:
What is the molarity of 12.5 L of solution made using 1.5 moles of KCl?
What is the molarity of 250 mL of solution made using 7.50 g of NaOH?
How many moles of NaI are needed to make 75 mL of a 0.25 M solution?
How many liters of solution can be made from 5.65 g of NaCl if the desired molarity is 0.500 M?
Open Note Quiz – The Mole and Molar Mass (10 points)
1. What is a mole?
____________________
2. How much is the Avogadro’s number?
____________________
3. What is the mass of 1 mole of sodium?
____________________
4. How many atoms are in 1 mole of magnesium?
____________________
5. What color was used to print the atomic mass on your periodic table? ____________________
6. What label is used for molar masses?
____________________
7. What is the molar mass of aluminum?
____________________
8. What is the molar mass of rubidium chloride, RbCl ?
____________________
9. What is the molar mass of BF3?
____________________
10. What is the molar mass of Cu3(PO4)2
____________________
Open Note Quiz – The Mole and Molar Mass (10 points)
1. What is a mole?
____________________
2. How much is the Avogadro’s number?
____________________
3. What is the mass of 1 mole of sodium?
____________________
4. How many atoms are in 1 mole of magnesium?
____________________
5. What color was used to print the atomic mass on your periodic table? ____________________
6. What label is used for molar masses?
____________________
7. What is the molar mass of aluminum?
____________________
8. What is the molar mass of rubidium chloride, RbCl ?
____________________
9. What is the molar mass of BF3?
____________________
10. What is the molar mass of Cu3(PO4)2
____________________
Homework: Percent Composition
1. If 2.50 g of iron react with chlorine, 4.76 g of iron(III) chloride (FeCl3) is formed. What is the percent composition by
mass of iron in the compound?
2. What is the percent composition of carbon in the compound sucrose (C12H22O11)?
3. What is the percent composition of nitrogen in the compound ammonia (NH3)?
4. What percent of glucose (C6H12O6), by mass, is oxygen?
5. Table salt is made from a reaction of sodium metal with chlorine gas. What is the percent composition of sodium in
table salt (NaCl) if 2.50 grams of sodium react to form 6.36 g of NaCl.
Homework: Using Moles and Avogadro’s Number
1. A piece of gold contains 0.35 moles. How many gold atoms are in this piece of metal?
2. A reaction needs 7.25 x 1023 atoms of barium. How many moles of barium are needed?
3. A chemical reaction produces 2.75 moles of lead. How many atoms of lead were produced?
4. How many carbon dioxide molecules (CO2) are in 4.42 moles of the gas?
5. 9.25 x 1022 water molecules are produced from a reaction. How many moles is this?
6. If 1.75 x 1024 glucose molecules were produced from photosynthesis, how many moles were made?
Review:
1. How many moles of silver are in a sample with a mass of 21.5 grams?
2. A sample of calcium iodide (CaI2) contains 2.35 moles. How many grams is this?
Homework: Conversions Involving Mass and Avogadro’s Number
1. How many atoms are in a 3.75 gram sample of silver?
2. What is the mass of 3.54 x 1024 atoms of calcium?
3. How many molecules are in a 7.23 gram sample of magnesium chloride (MgCl2)?
4. What is the mass of 7.89 x 1023 molecules of sulfur dioxide (SO2)?
5. How many molecules of potassium phosphate (K3PO4) are in a 12.75 gram sample of the compound?
6. What is the mass of 9.12 x 1024 molecules of aluminum sulfate (Al2(SO4)3)?
Review:
1. How many atoms are in 3.87 moles of iron(II) oxide (FeO)?
2. What is the mass of 4.21 moles of water?
Review of Mole Conversions
1. How many atoms are in 1 mole of gold? (Hint: No calculation necessary)
2. What is the mass of 1 mole of calcium? (Hint: No calculation necessary)
3. What is the mass of 3.97 x 1023 atoms of aluminum?
4. How many moles of copper would contain 3.01 x 1023 atoms?
5. How many grams of sulfur are in a 1.5 mole sample of the element?
6. An experiment requires 10.5 grams of magnesium chloride (MgCl2). How many moles is this?
7. How many calcium sulfate (CaSO4) molecules are in a 2.45 mole sample of the compound?
8. How many molecules are in 65.5 grams of lithium sulfide (Li2S)?
9. What is the mass of 7.65 x 1024 strontium hydroxide molecules (Sr(OH)2)?
10. What is the mass of 1.97 x 1024 zinc chloride molecules (ZnCl2)?
Homework: Molarity
1. What is the molarity of a 3.5 L solution containing 90.0 g of NaCl?
2. How many moles of HCl are needed to make 0.8 L of a 0.5 M solution?
3. How many liters of a 1.5 M solution can be made from 14.5 g of KI?
4. What is the molarity of 2.0 L of solution containing 5.75 g of CaO?
5. How many liters of a 12.0 M solution can be made from 75.5 g of NaOH?
6. How many grams of BaSO4 are needed to make 2.5 L of a 1.75 M solution?
*
In Class: Molarity Practice
1. What is the molarity of a 5.5 L solution containing 95.5 g of NaOH?
2. How many moles of H3PO4 are needed to make 1.25 L of a 0.75 M solution?
3. How many liters of a 7.5 M solution can be made from 85.5 g of H2CO3?
4. What is the molarity of 1.5 L of solution containing 12.75 g of KMnO3?
5. How many liters of a 7.5 M solution can be made from 50.25 g of H2S?
6. How many grams of Ca3(PO4)2 are needed to make 3.5 L of a 2.5 M solution?
Unit 4 Review:
1. Calculate the molar mass of sucrose (C12H22O11).
2. Determine the percent composition by mass of chlorine in Mg(ClO3)2.
3. A reaction between potassium and chlorine gas produces 7.50 grams of the compound KCl. If 2.67 grams of
potassium are allowed to react, what is the experimental percent composition by mass of potassium in potassium
chloride?
4. How many moles would contain 3.21 x 1023 atoms of Na?
5. If 58.9 grams of magnesium are produced, how many moles of magnesium are produced?
6. How many grams of bromine are in 2.6 moles of the element?
7. What is the mass of 2.58 x 1024 molecules of Na2SO4?
8. How many water molecules are in 19.6 grams of the compound?
9. How many moles of MgCl2 are needed to make 2.50 L of a 0.450 M solution?
(Formula: moles = Molarity x Liters)
10. What is the molarity of 0.750 L of solution containing 45.0 grams of AgNO3?
(Formula: Molarity = moles/Liters)