Homework: Moles

Write answers using complete sentences.
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1. What do chemical changes and physical changes have in common?
2. How are chemical changes and physical changes different?
3. How does the mole make it possible to count atoms and molecules?
4. What is the difference between mass and quantity?
5. 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.
6. 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 and the mass of H₂O that have an equal number of molecules.
   
   

Moles: Quantities 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.

7. CO₂
8. Ca₃(PO₄)₂

9. C₆H₁₂O₆
10. 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.

11. 5.9 mol CO₂
12. 3.8 × 10^-3 mol Ca₃(PO₄)₂

13. 1.2 kg C₆H₁₂O₆
14. 37.98 g AgNO₃

Comparing Quantities

Compare the following pairs of substances on the basis of the number of particles (the quantity, not the mass). Which one has more particles? Indicate your answer with a greater-than sign (>), less-than sign (<), or an equal sign.

15. 65.39 g Zn        238.0289 g U
16. 116.89 g NaCl        117.56 g Ca(OH)₂

17. 30.429 g MnO₂        60.052 g CaCO₃
18. 49.542 g H₂O        116.695 g BaSO₄

Big Numbers

Use the information from numbers 11 - 15 to calculate the number of molecules in each of those problems.

19. No. 11 
20. No. 12 

21. No. 13 
22. No. 14 

Challenge Questions

These questions are designed to put your understanding of this material to its limits. Mastering these questions will make the difference.

23. You have been given a container which weighs 49.87 g. You place a sample of C₆H₁₂O₆ into it and weigh it and now it weighs 92.54 g. How many molecules of sugar are in the container?
24. 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?