# CHEMISTRY COMPUTING FORMULA MASS WORKSHEET

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1 CHEMISTRY COMPUTING FORMULA MASS WORKSHEET Directions: Find the formula mass of the following compounds. Round atomic masses to the tenth of a decimal place. Place your final answer in the FORMULA MASS COLUMN. Problem Set-up example: Find the formula mass of Ca(NO3)2 Ca: 1 x 40.1 = 40.1 N: 2 x 14.0 = 28.0 O: 6 x 16.0 = 96.0 Formula Mass = COMPOUND FORMULA MASS COMPOUND FORMULA MASS AgNO2 ZnCl2 NiSO3 K3PO4 Ca3(PO4)2 Al2(SO4)3 HgSO4 MgCrO4 Fe(NO3)3 CaC4H4O6 KBr NaCl BeCr2O7 K2Cr2O7 Co(ClO3)2 H2SO4 Cu2C4H4O6 Cu(OH)2 CuSO4. 7 H2O MgSO4. 5 H2O

2 CHEMISTRY COMPUTING FORMULA MASS WORKSHEET Directions: Find the formula mass of the following compounds. Round atomic masses to the tenth of a decimal place. Place your final answer in the FORMULA MASS COLUMN. Problem Set-up example: Find the formula mass of Ca(NO3)2 Ca: 1 x 40.1 = 40.1 N: 2 x 14.0 = 28.0 O: 6 x 16.0 = 96.0 Formula Mass = COMPOUND FORMULA MASS COMPOUND FORMULA MASS AgNO ZnCl NiSO K3PO Ca3(PO4) Al2(SO4) HgSO MgCrO Fe(NO3) CaC4H4O KBr 119 NaCl 58.4 BeCr2O K2Cr2O Co(ClO3) H2SO Cu2C4H4O Cu(OH) CuSO4. 7 H2O MgSO4. 5 H2O 210.4

3 CHEMISTRY Molar Ratios The molar ratio is an important comcept in solving stoichiometry problems. The sources for these ratios are the coefficients of a balanced equation. Example 1: 2 H2 + O2---> 2 H2O What is the molar ratio between H2and O2? MOLAR RATIOS WORKSHEET Practice Problems Following each equation are two requests for molar ratios from the equation. 1) N2 + 3 H2 ---> 2 NH3 Write the molar ratios for: N2 to H2 and NH3 to H2 Answer: two to one. So this ratio is written as a fraction is 2 1 What is the molar ratio between O2and H2O? 2) 2 SO2 + O2 ---> 2 SO3 Write the molar ratios for: O2 to SO3 and O2 to SO2 Answer: one to two. As a fraction, it is: 1 2 What is the molar ratio between H2 and H2O? Answer: two to two or: 2 2 This reduces to one to one, but leave it written as 2 to 2. Example 2: 2 O3 ---> 3 O2 The exact molar ratio you would use depends on how the problem is worded. What is the molar ratio between O3and O2? 2 3 What is the molar ratio between O2and O3? 3 2 3) PCl3 + Cl2 ---> PCl5 Write the molar ratios for PCl3 to Cl2 and PCl3 to PCl5 4) 4 NH3+ 3 O2 ---> 2 N2 + 6 H2O Write the molar ratios for NH3 to N2 and H2O to O2 5) Fe2O3 + 3 CO ---> 2 Fe + 3 CO2 Write the molar ratios for CO to CO2 and Fe to CO

4 CHEMISTRY STOICHIOMETRY The Mathematics of Chemical Equations (Stoichiometry) A major task of the chemist is to project how much product can be produced from a certain amount of reactant. The amount of product produced must have more value than the reactants plus the added cost of safely disposing of any waste product produced. The cost of the energy used in the reaction or the cost of disposing of any heat given off by the reaction must also be taken into consideration. A chemical engineer must be able to calculate the amounts of all reactants and products in order to determine if the process is economical. This type of calculation is called stoichiometry. A flow chart for solving stoichiometry problems: Mass (g,kg, etc.) Volume (L, ml. etc.) Moles Start With or # of Items (atoms,molec.) Convert to of Multiply by of Given reactant or product Given Sample Problem I II III IV What mass, in grams, of KClO3 is consumed when 90 grams of O2 is produced according to the following reaction: X (Unknown) 90g( Given) At STP: 1 mole = 6.02 x items 1 mole(g) = 22.4 Liters 2 KClO3(s) > 2 KCl(s) + 3 O2(g) 2 moles 3 moles X = 90 g O2 1 mole O2 2 mole KClO g KClO3 = g KClO3 32 g O2 3 moles O2 1 mole KClO3 I II III IV Mole Ratio from the Balanced Chemical Equation Convert to Mass (g,kg, etc.) Volume (L, ml. etc.) or # of Items (atoms,molec.) of Unknown reactant or product)

5 CHEMISTRY Stoichiometry Practice [Mole-Mass] Multiple Choice: Show your set-up in the space provided and circle the answer of your choice. (1) Given the balanced equation: 2 NO > N2O4 What mass, in grams, of N2O4 is produced when 10 moles of NO2 is consumed? a) 153 b) 690 c) 368 d) 460 e) 1150 (2) Given the balanced equation: ZnSO4 + SrCl > SrSO4 + ZnCl2 What number of moles of SrCl2 is consumed when 54 g of ZnCl2 is produced? a) 0.16 b) 0.3 c) 0.79 d) 1.58 e) 0.4 (3) Given the balanced equation: Pb(NO3)2 + K2CrO > PbCrO4 + 2 KNO3 What number of moles of Pb(NO3)2 is consumed when 54 g of KNO3 is produced? a) 0.13 b) 0.18 c) 0.27 d) 1.34 e) 0.67 (4) Given the balanced equation: 2 C8H O > 16 CO H2O What number of moles of CO2 is produced when 60 grams of C8H18 is consumed? a) 3.37 b) 7.02 c) 5.26 d) 2.11 e) 4.21

6 CHEMISTRY Stoichiometry Practice [Mole-Mass] Answers: (1) 460 (2) 0.4 (3) 0.27 (4) 4.21

7 CHEMISTRY Stoichiometry Practice(Mass-Mass) Multiple Choice: Show your set-up in the space provided and circle the answer of your choice. (1) Given the following reaction: 2 AlI3 + 3 HgCl > 2 AlCl3 + 3 HgI2 What mass, in grams, of AlI3 is consumed when 46 grams of HgI2 is produced? a) 27.5 b) 6.9 c) d) 82.5 e) 68.8 (2) Given the following reaction: CaBr2 + 2 KOH > Ca(OH)2 + 2 KBr What mass, in grams, of CaBr2 is consumed when 96 g of Ca(OH)2 is produced? a) 173 b) 52 c) 86 d) 155 e) 259 (3) Given the following reaction: 3 H2 + N > 2 NH3 What mass, in grams, of NH3 is produced when 77 g of N2 is consumed? a) 187 b) 31.2 c) 18.7 d) 46.8 e) 93.5 (4) Given the following reaction: 3 AgNO3 + K3PO > Ag3PO4 + 3 KNO3 What mass, in grams, of Ag3PO4 is produced when 19 g of K3PO4 is consumed? a) 46.8 b) 15 c) 37.5 d) 18.7 e) 112.4

8 CHEMISTRY Stoichiometry Practice(Mass-Mass) Answers: 1) ) 259 3) ) 37.5

9 CHEMISTRY Stoichiometry Practice(Mass-Molecule) Multiple Choice: Show your set-up in the space provided and circle the answer of your choice. (1) Given the balanced equation: 2 Al + 6 NaOH > 2 Na3AlO3 + 3 H2 What mass, in grams, of Na3AlO3 is produced when 6 x 1023 molecules of NaOH is consumed? a) 240 b) 80 c) 64 d) 9.6 e) 48 (2) Given the balanced equation: 3 CuS + 8 HNO > 3 Cu(NO3)2 + 3 S + 2 NO + 4 H2O What number of molecules of Cu(NO3)2 is produced when 67 g of HNO3 is consumed? a) 7.18 b) 3.19 c) 5.98 d) 1.44 e) 2.39 [all x 1023] 3. Given the balanced equation: 3 CuS + 8 HNO > 3 Cu(NO3)2 + 3 S + 2 NO + 4 H2O What number of molecules of NO is produced when 8 grams of S is produced? a) 1.99 b) 2.99 c) 0.33 d) 1.5 e) 1 [all x 1023] 4. Given the balanced equation: 8 Fe + S > 8 FeS What mass, in grams, of S8 is consumed when 5 x 1023 molecules of Fe is consumed? a) 1.67 b) 3.34 c) d) 5.57 e) 6.69

10 CHEMISTRY Stoichiometry Practice(Mass-Molecule) Answers: 1) 48 2) 2.39 x ) 1 x ) 3.34

11 CHEMISTRY STOICHIOMETRY WORKSHEET A. MASS - MASS PROBLEMS 1. What mass of oxygen reacts when 84.9 g of iron is consumed in the follolwing reaction: Fe + O > Fe2O3 Given the following reaction: Al2(SO4)3 + 6 NaOH > 2 Al(OH)3 + 3 Na2SO4 2. What mass of Al(OH)3 is produced if 22.7 g of NaOH is consumed? Given the following reaction: P4 + 5 O > P4O10 3. What mass of oxygen will react with 7.75 g of P4?

12 CHEMISTRY STOICHIOMETRY WORKSHEET B. MASS - VOLUME and VOLUME - VOLUME PROBLEMS Since chemical equations for chemical reactions state the relative numbers of moles for each reactant and product, these numbers can tell us the volumes at STP for those substances that are gases. Recall that the volume occupied by 1 mole of any gas at STP is 22.4 Liters. This relationship between moles (and hence, mass) and volumes can be used to solve problems of the types often called mass - volume and volume - volume. For the reaction MnO2(gas) + 4 HCl(aq) > MnCl2(aq) + Cl2(g) + 2 H2O(l) 1. what volume of Cl2(g) measured at STP is produced when 7.65 g of HCl(aq) reacts? For the reaction 3 H2(g) + N2(g) > 2 NH3(g) 2. what mass of NH3(g) is produced when 2.15 L of H2(g) measured at STP reacts? For the reaction 3 H2(g) + N2(g) > 2 NH3(g) 3. what volume of NH3(g) measured at STP is produced when 2.15 L of H2(g) reacts?

13 CHEMISTRY STOICHIOMETRY WORKSHEET C. MASS - MOLECULE and MOLECULE - MOLECULE PROBLEMS For the reaction, at STP 3 H2(g) + N2(g) > 2 NH3(g) 1. what mass of NH3(g) is produced when 2 x 1023 molecules of N2 reacts? For the reaction, at STP 2 C2H2(g) + 5 O2(g) > 4 CO2(g) + 2 H2O(g) 2. what number of molecules of CO2(g) will be produced if 3 x 1024 molecules of O2(g) reacts.

14 CHEMISTRY STOICHIOMETRY WORKSHEET D.VOLUME - MOLECULE PROBLEMS 1. What number of molecules of O2 is consumed when 33.6 liters of STP H2O is produced according to the following reaction: 4 NH3 (g) + 5 O2 (g) > 4 NO (g) + 6 H2O (g) 2. What number of liters of STP CO2 is produced when 7 x 1023 molecules of O2 is consumed? C3H8(g) + 5 O2(g) > 3 CO2(g) + 4 H2O(g)

15 CHEMISTRY STOICHIOMETRY WORKSHEET 1) 2N2H4(l) + N2O4(l)----> 3N2(g) + 4H2O(l) If g of N2H4 is used, what mass of nitrogen is produced? 2) 10.6 g of magnesium react with excess hydrochloric acid. a) Write the balanced equation for the reaction. b) What mass of hydrogen gas is produced? c) Classify this reaction as single or double displacement, decomposition, synthesis, or combustion. 3) Potassium hydroxide decomposes into potassium oxide and water. a) Write the balanced equation for the reaction. b) What is the amount of water formed if 34.9 g of potassium hydroxide are used?

16 CHEMISTRY STOICHIOMETRY WORKSHEET 4) Barium hydroxide reacts with sulfuric acid. a) Write the balanced equation for the reaction. b) What mass of barium hydroxide is needed to completely react with 9.58 g of sulfuric acid? c) Classify this reaction as single or double displacement, decomposition, synthesis, or combustion. 5) The actual amount of product produced in a reaction is g, although a mass-mass calculation predicted g. What is the percentage yield of this product? 6) Hydrogen burns in oxygen according to the following reaction: 2H2 (g) + O2 (g)------> 2H2O(g) What is the percentage yield if 9.28 g of oxygen react with hydrogen to produce 8.81 g of water?

17 CHEMISTRY STOICHIOMETRY WORKSHEET 7) 28.0 g of magnesium carbonate reacts with sulfuric acid. What mass of water is produced? 8) Na2SiO3(s) + 8HF(aq) > H2SiF6(aq) + 2NaF(aq) + 3H2O(l) If 17.4 g of HF is used, what mass of H2SiF6 is produced? 9) 17.1 g of C2H6 is burned in oxygen. What mass of oxygen was consumed? (Assume complete combustion.)

18 CHEMISTRY STOICHIOMETRY WORKSHEET KEY 1) 14.2 g 2) a) Mg + 2HCl -----> H2 + MgCl2 b) g c) Single displacement 3) a) 2KOH > K2O + H2O b) 5.60 g 4) a) Ba(OH2 + H2SO > 2H2O + BaSO4 b) 16.7 g c) double displacement 5) 70.68% 6) 84.4% 7) 5.98g 8) 15.7g 9) 63.8g

19 CHEMISTRY Stoichiometry Worksheet [Mass Mass] 1. How many grams of C2H2 will be produced, if 7.00g of Ca(OH)2 are also produced in the following reaction? CaC2 + 2H2O > C2H2 + Ca(OH)2 2. How many grams of H2O will be produced, if 26.31g of CO2 are also produced in the following reaction? C3H8 + 5O > 3CO2 + 4H2O 3. How many grams of H2O will be produced by the combustion of grams of C2H4? C2H4 + 3O > 2CO2 + 2H2O 4. How many moles of HCl will react with 18.13g of SrO? SrO + 2HCl > SrCl2 + H2O

20 CHEMISTRY Stoichiometry Worksheet [Mass Mass] 5. How many grams of NH3 will be produced, if 97.77g of CaCO3 are also produced in the reaction below? CaCN2 + 3H2O > CaCO3 + 2NH3 6. How many grams of H2O are needed if 41.85g of O2 are to be produced from the reaction below? 2K2O2 + 2H2O > 4KOH + O2 7. How many grams of NO will be produced, if 1.93g of H2O are also produced in the reaction below? 4NH3 + 5O > 4NO + 6H2O 8. In the chemical reaction below, how many grams of HCl will be produced by the reaction of g of CCl4? CCl4 + 2HF > CCl2F2 + 2HCl

21 CHEMISTRY Stoichiometry Worksheet [Mass Mass] 9. In the chemical reaction below, how many grams of KCN will react with 81.55g of H2SO4? 2KCN + H2SO > K2SO4 + 2HCN 10. How many grams of Fe2O3 will react with grams of C in the REDOX reaction below? 2Fe2O3 + 3C > 4Fe + 3CO2 11. In the following unbalanced combustion reaction, how many grams of C8H18 will react with 4.78g of O2? C8H18 + O > CO2 + H2O 12. In this unbalanced chemical reaction Fe3O4 + H > Fe + H2O How many grams of H2O will be produced, if 41.95g of Fe3O4 are reacted completely with hydrogen?

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