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## Homework: Moles

Show work for all calculations!

1. How are chemical changes and physical changes different? Give an example of each kind of change. Write your explanation based on events that happen at the molecular level.
2. How does the mole make it possible to count atoms and molecules?
3. Explain why the Law of Conservation of Matter is true based on what you know about physical and chemical changes at the atomic/molecular level.

#### Moles: Numbers and Masses

##### Molar Masses

For each of the following elements or compounds calculate the mass of 1 mole of particles of that substance. Express answers in units of g/mol. Use at least five significant figures for the mass of each element when calculating molar masses.

1. CO2
2. Ba3(PO4)2
1. C6H12O6
2. AgNO3

##### Putting Molar Masses to Work

For each of the masses, convert to number of moles. For each quantity given in moles, convert to mass in grams. Express each answer with the correct number of significant figures.

1. 5.9 mol CO2
2. 3.8 × 10-3 mol Ba3(PO4)2
1. 1.2 kg C6H12O6
2. 37.98 g AgNO3

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##### Comparing Moles

Compare the following pairs of samples on the basis of the number of particles (the number of moles, not the mass). Which one has more particles? Circle the sample that has the larger number of particles.

 65.39 g Zn      238.0289 g U 116.89 g NaCl      117.56 g Ca(OH)2 30.429 g MnO2      60.052 g CaCO3 49.542 g H2O      116.695 g BaSO4

##### Big Numbers

Use the information from numbers 10 - 13 to calculate the number of molecules in each of those problems.

1. No. 8
2. No. 9
1. No. 10
2. No. 11
1. You have been given a container which weighs 49.87 g. You place a sample of glucose (C6H12O6) into it and weigh it and now it weighs 92.54 g. How many molecules of glucose are in the container?
2. Chloral hydrate (C2H3Cl3O2) is a drug formerly used as a sedative and hypnotic. It is the compound used to make “Mickey Finns” in detective stories.
1. Calculate the molar mass of chloral hydrate.
2. How many moles of C2H3Cl3O2 molecules are in 500.0 g of chloral hydrate?
3. What is the mass in grams of 2.0 × 10-2 mol chloral hydrate?
4. How many chlorine atoms are in 5.0 g of chloral hydrate?
5. What mass of chloral hydrate would contain 1.0 g Cl?
6. What is the mass of exactly 500 molecules of chloral hydrate?
This homework belongs with the Moles Group Activity.
Moles Practice Calculations
Last updated: Mar 25, 2021       Home