1. Std 3 Stoich CST Review Answers

2. Standard 3a: Students know how to describe chemical reactions by writing balanced equations. 1) C 3 H 8 + O 2 → CO 2 + H 2 O This chemical equation represents the combustion of propane. When correctly balanced, the coefficient for water is: a 2.b 4.c 8.d 16. 2) Which of the following is a balanced equation for the combustion of ethanol (CH 3 CH 2 OH)? a. CH 3 CH 2 OH + 2O 2 → CO 2 + 2H 2 Ob. CH 3 CH 2 OH + 3O 2 → 2CO 2 + 3H 2 O c. CH 3 CH 2 OH + O 2 → 2CO 2 + 3H 2 Od. CH 3 CH 2 OH + 2O 2 → 3CO 2 + 2H 2 O 3) Hydrazine, N 2 H 4, and dinitrogen tetroxide, N 2 O 4, will react and form gaseous nitrogen, N 2, and water. Which of these represents a properly balanced equation for this reaction? a. N 2 H 4 + N 2 O 4 → N 2 + H 2 Ob. 2N 2 H 4 + N 2 O 4 → 2N 2 + 4H 2 O c. 2N 2 H 4 + N 2 O 4 → 3N 2 + 4H 2 Od. 2N 2 H 4 + 3N 2 O 4 → 5N 2 + 6H 2 O 4) __ NH 3 (g) + __ O 2 (g) → __N 2 (g) + __ H 2 O (g) When the reaction above is completely balanced, the coefficient for NH 3 will be: A 2.B 3.C 4.D 6. 5) A number written in front of a chemical formula is: a. Coefficientb. spectator ionc. reactantd. product

3. Standard 3b: Students know that the quantity of 1 mole is set by defining one mole of carbon 12 to have a mass of exactly 12 grams. 6) How many moles of carbon-12 are contained in exactly 6 grams of carbon-12? A 0.5mole B 2.0 molesC 3.01 ×10 23 moles D 6.02 ×10 23 moles 7) True or False: One mole of any substance contains 6.98x10 23 particles of the substance. 8) True or False: There are 6.02 x 10 23 molecules of water in 1.0 moles of water.

4. #9 How many atoms are contained in 195 g of platinum (Pt)? (use a 2 column t-chart) 195 g Pt Given # Molar mass from periodic table 1 mole Pt 6.02 x 10 23 atoms Pt

5. #10 How many moles are in 1.2 x10 24 atoms of a gas? (use simple t-chart) 1.2 x 10 24 atoms 6.02 x 10 23 atoms Given # 1 mole 2 moles of gas

6. #11 How many moles of CH 4 are contained in 160 grams of CH 4 ? (use 2 column t-chart) 160 g CH 4 16 g CH 4 Given # Molar mass from periodic table 1 mole CH 4 10 moles CH 4

7. #12 How many atoms are in a neon sample with a mass of 60 grams?(use a 3 column t-chart) 60 g Ne 20 g Ne Given # Molar mass from periodic table 1 mole Ne 6.02 x 10 23 atoms Ne 1.8 x 10 24 atoms Ne

8. #13 How many moles of chlorine gas (Cl 2 ) are contained in 3.01x10 23 molecules? ( use a 2 column t-chart) 3.01x10 23 molecs Cl 2 6.02x10 23 molecs Cl 2 Given # 1 mole Cl 2 0.5 moles Cl 2 #14 Which of the following has the smallest molar mass? a. CO b. H 2 O c. CO 2 d. H 2 O 2

9. #15 How many moles does 35g of Cl 2 contain? (use a 2 column t- chart) 35 g Cl 2 70 g Cl 2 Given # 1 mole Cl 2 0.5 moles Cl 2 Molar mass from periodic table

10. 16. What volume will 1 moles of Br 2 occupy at STP? a. 156.8L b. 22.4L c. 154.4Ld. 78.4 L

11. #17 11.2 L of a gas will have how many molecules? ( use a 3 column t-chart) 11.2 L gas 22.4 L gas Given # 1 mole gas 3.01 x 10 23 molecules gas 1 mole gas 6.02 x 10 23 molecules

12. #18 CH 4 + 2O 2 → CO 2 + 2H 2 O If 1 mole of methane reacts with 2 moles of oxygen, then: (use logic – not tchart) A 6.02 ×10 23 molecules of CO 2 and 6.02 × 10 23 molecules of H 2 O are produced. B 1.2×10 24 molecules of CO 2 and 1.2× 10 24 molecules of H 2 Oare produced. C 6.02 ×10 23 molecules of CO 2 and 1.2×10 24 molecules of H 2 Oare produced. D 1.2 ×10 24 molecules of CO 2 and 6.02 ×10 23 molecules of H 2 Oare produced.

13. #19 Fe 2 O 3 + 3CO → 2Fe + 3CO 2 In this reaction, how many grams of Fe 2 O 3 are needed to react with 84 g of CO? (need 4 column t-chart) 84 g CO 28 g CO Given # Molar mass from periodic table 1 mole CO 3 moles CO 1 mole Fe 2 O 3 160 g Fe 2 O 3 Mole ratio from equation 1 mole Fe 2 O 3 160 g Fe 2 O 3 Molar mass from periodic table

14. #20 Mg 3 N 2 (s) + 6H 2 O (l) → 3 Mg(OH) 2 (s) + 2NH 3 (aq) If 54.0 grams of water are mixed with excess magnesium nitride, then how many grams of ammonia (NH 3 ) are produced? (need 4 column t-chart) 54 g H 2 O 18 g H 2 O Given # Molar mass from periodic table 1 mole H 2 O 6 moles H 2 O 2 mole NH 3 17 g NH 3 Mole ratio from equation 1 mole NH 3 17 g NH 3 Molar mass from periodic table

15. #21 A mass of 5.4 grams of aluminum (Al) reacts with an excess of copper (II) chloride (CuCl 2 ) in solution, as shown: 3CuCl 2 + 2Al → 2AlCl 3 + 3Cu What mass of solid copper (Cu) is produced? (need 4 column t-chart) 5.4 g Al 27 g Al Given # Molar mass from periodic table 1 mole Al 2 moles Al 3 mole Cu 19 g Cu Mole ratio from equation 1 mole Cu 64 g Cu Molar mass from periodic table

16. #22 Stoichiometry is based on the law of conservation of: a. Volume b. reactantsc. charged. mass

17. #23 How many moles of Cu are produced when 1.2x10 24 atoms of Al are used according to the following reaction: 3CuCl 2 + 2Al → 2AlCl 3 + 3Cu (need 3 column t-chart) 1.2x10 24 atoms of Al 6.02x10 23 atoms of Al Given # 1 mole Al 3 moles Cu 2 mole Al 3 moles Cu

18. #24 Mg 3 N (s) + 6H 2 O (l) → 3 Mg(OH) 2 (s) + 2NH 3 (aq) If 67.2 L of water are mixed with excess magnesium nitride, then how many moles of ammonia (NH 3 ) are produced? (need 3 column t-chart) 67.2 L H 2 0 22.4 L H 2 0 Given # 1 mole H 2 0 1 moles NH 3 6 moles H 2 0 2 moles NH 3 Mole ratio from equation

19. 25. Mg 3 N (s) + 6H 2 O (l) → 3 Mg(OH) 2 (s) + 2NH 3 (aq) What is the mole ratio of Mg 3 N to Mg(OH) 2 ?(no tchart) A 1:1 B 1:3 C 1:2 D 3:1 The coefficients (big # in front of formula) tell you how many molecules are involved for that substance but also tell you how many moles are involved.