1. The number 6.02 x 10²³ is a very important number in chemistry. Whose number is this?
a. Kelvin’s Number
b. Boyle’s Number
c. Avogadro’s Number
d. Charles’s Number

2. Which of the following are NOT 1 mole?
a. 2.0 g of H2
b. 35.5 g Cl2
c. 6.02 x 10²³ molecules O2
d. 55.8 g Fe

3. Which of the following sets contain the same number of atoms?
a. 12.0 g C and 2.0 g H
b. 32.0 g S and 32.0 g O
c. 58.9 g Co and 3.5 g Li
d. 107.9 g Ag and 27.0 g Al

4. Which of the following DOES NOT have the same mass as 1 atom of S?
a. 2 atoms of O
b. 2 atoms of C
c. 8 atoms of He
d. 16 molecules of H2

5. When chemical equations are balanced, they are said to follow the
a. Octet Rule
b. Law of Gravity
c. Law of Conservation of Mass/Matter
d. Ideal Gas Law

6. Which of the following chemical equations is balanced?
a. H3PO4 + Ba(OH)2 ---> Ba3(PO4)2 + H2O
b. 3H3PO4 + 2Ba(OH)2 ---> 2Ba3(PO4)2 + 3H2O
c. 2H3PO4 + 3Ba(OH)2 ---> 2Ba3(PO4)2 + 6H2O
d. 2H3PO4 + 3Ba(OH)2 ---> Ba3(PO4)2 + 6H2O

7. How many grams of Na are in 2.80 x 10²⁴ atoms of Na?
a. 4.65
b. 107
c. 6.02
d. 49.5

8. Which of the following quantities represent one mole?
a. 28.0 g N2
b. 42.0 g Ne
c. 16.0 g H2O
d. 1.0 g H2

9. What is the relationship between moles and particles?
10. What is the relationship between moles and mass?
11. What is the molar mass (MM) of Ca₃(PO₄)₂?
12. How many atoms of vanadium are in 7.4 moles of vanadium?
13. What is the mass of 3.45x10²² molecules of C₆H₁₂O6?
14. How many hydrogen atoms are in 4.35 grams of water?
15. How many moles of NH3 are in a sample that weighs 38.5 g?
16. How many kg are there in a sample of 5.2 moles of Pb?
17. How many moles are present in 34 grams of Cu(OH)₂?

18. In the decomposition of 2.8 moles of phosphorous pentachloride, how many moles of chlorine gas (note that chlorine is a diatomic molecule) would be formed?

Given:   2CO (g) + O2 (g) ---> 2CO2 (g) (Use for Questions 19-22)
19. How many moles of CO gas are needed to prepare 24 moles of CO2?
20. How many moles of O2 are needed to react with 18 moles of CO?
21. How many grams of CO are needed to react with 4.20 moles of O2?
22. How many grams of CO2 can be prepared from 1.80 moles of O2?

Given: 2H2 (g) + O2 (g) --> 2H2O (l)   (Use for Questions 23-25)
23. How many moles of H2O can be formed from 1.8 mol O2?
24. What mass in grams of H2 is needed to react with 2.8 x 10²⁴molecules O2?
25. How many molecules of H2 does it take to react with 2.4 g O2?

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1. ANSWER: C – This is Avogadro’s number, which is the number of particles in a mole of any substance
2. ANSWER: B – Since Cl2 is diatomic, 1 mole of it would weigh 2 x 35.5 = 71.0 g Cl2
3. ANSWER: D – 12.0 g C is 1 mol of C atoms, but 2.0 g H is 2 mol of H atoms; 32.0 g S is 1 mol of S atoms, but 32.0 g O is 2 mol O atoms; 58.9 g Co is 1 mol Co atoms, but 3.5 g Li is ½ mol Li atoms; 107.9 g Ag is 1 mol of Ag atoms and 27.0 g Al is 1 mol of Al atoms.
4. ANSWER: B – 1 atom of S = 32.0 amu. 2 atoms of O weighs 2 x 16.0 amu = 32.0 amu so that is the same, 8 atoms of He weighs 8 x 4.0 amu so that is also the same, and 16 molecules of H2 weighs 16 x 2.0 amu...

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