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Homework: Moles

Write answers using complete sentences.
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.

  1. 65.39 g Zn      238.0289 g U
  2. 116.89 g NaCl      117.56 g Ca(OH)2
  1. 30.429 g MnO2      60.052 g CaCO3
  2. 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?
  3. Here is a chemical reaction: 1CO2 + 1H2O --> 1H2CO3
    It says that one molecule of carbon dioxide (CO2) reacts with one molecule of water (H2O) to make one molecule of carbonic acid (H2CO3). In reality, you cannot count the molecules because they are too small. Instead you must use mass. Using what you know about moles and molar mass find the mass of CO2 that would be required to react with 36.0 g of H2O to make 124 g of H2CO3.

  4. Here is another chemical reaction: 2H2 + 1O2 --> 2H2O
    It says that two moles of hydrogen (H2) react with one mole of oxygen (O2) to make two moles of water (H2O). One mole of hydrogen has a mass of about 2 grams. One mole of oxygen has a mass of about 32 grams. And one mole of water has a mass of 18 grams. If you have 10 grams of hydrogen, how many grams of oxygen will react with it? Hint: convert to moles and consider that 1 mol of oxygen reacts with every 2 mol of hydrogen. Once you know how many moles, calculate the mass of oxygen using its molar mass.

This homework belongs with the Moles Group Activity.
Moles Practice Calculations
Last updated: May 02, 2016       Home