3-1 Unit 3 Moles & Stoichiometry At the end of this unit, you ll know A compound is a substance composed of two or more different elements that are chemically combined in a fixed proportion. A chemical compound can only be broken down by chemical means. Chemical compounds can be represented by a specific formula and assigned a name based on the IUPAC system. Types of chemical formulas include empirical, molecular, and structural. Empirical formulas show elements in their simplest whole number ratios. This may or may not be the same as the molecular formula. Molecular formulas show the actual number of atoms per element in a single molecule. Structural formulas show the number of each type of atom as well as their physical arrangement. All chemical reactions show a conservation of mass, energy and charge. A balanced chemical equation represents conservation of atoms. The coefficients in a balanced chemical equation can be used to determine mole ratios in the reaction. The formula mass of a substance is the sum of the atomic masses of its atoms. The molar mass (gram formula mass) equals the mass of one mole of that substance. The percent composition by mass of each element in a compound can be calculated mathematically. Types of chemical reactions include synthesis, decomposition single replacement, and double replacement. Page 1 of 1 Unit 3 Objectives.docx
Unit 3 - Moles and Stoichiometry 3-2 Term Balanced equation Coefficient Decomposition reaction Double-replacement reaction Empirical formula Formula mass (FM) Gram formula mass (GFM) Law of conservation of energy Law of conservation of mass Mole Molecular formula Definition a chemical equation in which the number of moles of each element on the reactants side is equal to the number of moles of each element on the products side the integer that appears in front of an element, molecule, or compound indicating the number of moles present a chemical reaction in which a compound is broken down into simpler substance Ex: AB à A + B a chemical reaction in which a metal replaces a metal AND a nonmetal replaces a nonmetal within two compounds; two compounds trade elements Ex: AB + XY à AY + XB formula for a compound which provides the simplest ratio of the elements present Ex: The empirical formula for the molecule C6H12O6 is CH2O the sum of the atomic masses of a substance in a.m.u. the sum of the atomic masses of a substance in grams in any chemical reaction, energy can neither be created nor destroyed; the energy of the reactants must be equal to the energy of the products in any chemical reaction, mass can neither be created nor destroyed; the mass of the reactants must be equal to the mass of the products a quantity of 6.02 x 1023 units of a substance; the amount of a substance equal to the sum of the atomic masses in grams; Avogadro s number formula for a compound which provides the number and identity of the atoms of each element present Ex: C6H12O6 Percent mass mass of part/mass of whole x 100% Single-replacement reaction Species Subscript Synthesis reaction a chemical reaction in which a metal replaces a metal OR a nonmetal replaces a nonmetal within a compound Ex: A + BC à AC + B the individual products and reactants in a chemical reaction the integer to the lower right of an element which indicates the number of atoms present in the compound a chemical reaction in which two or more substances combine to form a compound Ex: A + B à AB Page 1 of 1
Name Date 3-3 Period Elements and Compounds 1) Which of the following CAN be decomposed by chemical change? a) SO2 b) N2 c) Ne d) Al 2) Which of the following fictitious element symbols are legitimate? a) Cn b) HB c) zl d) r 3) Which of the following substances can not be decomposed by chemical change? a) Na b) HNO3 c) ZnCl2 d) C6H12O6 4) You have discovered a new element and name it. Which one of the following symbols may be used for your new element? a) U b) DG c) nd d) Sd 5) Which of the following substances can be decomposed by chemical change? a) Na b) Cl c) NaCl d) K 6) Which of the following represents a homogeneous mixture? a) NaCl (s) b) NaCl (l) c) NaCl (aq) d) NaCl (g) 7) Which of the following represents a heterogeneous mixture? a) air b) soil c) salt water d) sugar 8) Draw a particle diagram of a compound of CaCl2, using black solid circles to represent the Ca and empty circles to represent the Cl. Draw at least five molecules of CaCl2 in the box below: Page 1 of 2 3.1 w-1 elements and compounds.pub
Name Date 3-4 Period 9 Elements and Compounds 11 10 Label each of the following as Element, Compound, Mixture of elements, mixture of compounds, or mixture of both (elements and compounds.). 12 13 14 15 16 17 Page 2 of 2 3.1 w-1 elements and compounds.pub
M-NM Naming Compounds 3-5 1. NaBr 2. CaO 3. Li 2 S 4. MgBr 2 5. Be(OH) 2 6. NH 4 Cl 7. Fe(NO 3 ) 3 9. Cu 3 P 10. SnSe 2 11. GaAs 12. Pb(SO 4 ) 2 13. Be(HCO 3 ) 2 14. Mn 2 (SO 3 ) 3 15. Al(CN) 3 8. TiBr 3 NM-NM 16. SO 3 17. N 2 S 18. PH 3 19. BF 3 20. P 2 Br 4 21. CO 22. SiO 2 23. SF 6 24. NH 3 25. NO 2 Mixed 26. Fe(CN) 3 27. Mg 3 N 2 28. N 2 O 29. H 2 O 30. Na 2 CO 3 31. P 2 O 5 32. NH 3 33. FeSO 4 34. SiO 2 35. GaCl 3 36. CoBr 2 37. B 2 H 4 Page 1 of 1 3.2 w-1 Naming Compounds.docx
3-6 Molecular Formula from Name 1. magnesium acetate 2. boron carbide 3. calcium carbonate 4. aluminum carbonate 5. aluminum chloride 6. calcium chloride 7. ammonium chloride 8. sodium cyanide 9. sulfur dibromide 10. oxygen difluoride 11. carbon disulfide 12. magnesium hydroxide 13. potassium iodide 14. nitrogen monoxide 15. sodium nitrate 16. magnesium oxide 17. aluminum oxide 18. phosphorus pentafluoride 19. sodium phosphate 20. beryllium phosphide 21. lithium sulfate 22. diboron tetrahydride 23. nitrogen trichloride 24. dinitrogen trioxide Page 1 of 2 3.2 w-2 Molecular Formula From Name.docx
25. iron (III) sulfite 26. chromium (III) sulfide 27. calcium carbonate 28. sodium acetate 29. cobalt (II) fluoride 30. sodium phosphide 31. tin (IV) oxide 32. gold (III) bromide 33. copper (II) iodide 34. strontium chloride 35. lithium acetate 36. magnesium hydroxide 37. nickel (II) nitrate 38. chromium (III) sulfite 39. copper (II) sulfide 40. iron (III) bromide 41. aluminum nitride 42. calcium sulfate 43. sodium phosphate 44. iron (III) nitrate 45. ammonium carbonate 46. sulfur tetrafluoride 47. xenon tetrafluoride 48. dihydrogen monoxide 3-7 Page 2 of 2 3.2 w-2 Molecular Formula From Name.docx
Name Period 3-8 Writing Ionic Formulas Use the crisscross method to predict the simplest possible formula Na + Cl - OH - CO 3 2- SO 4 2- PO 4 3- NH 4 + K + Ca 2+ Mg 2+ Fe 3+ Al 3+ Co 3+ Fe 2+ H + Page 1 of 1 3.2 w-3 CrissCross.docx
Formulas 3-9 1. Explain the difference between a molecular formula and an empirical formula. 2. Write the empirical formula for each of the following: a. C 6 H 12 O 6 b. O 2 F 2 c. P 4 O 6 d. C 2 H 6 O 2 e. C 2 H 4 O 2 f. C 7 H 15 COOH 3. Write the molecular formula for butane. 4. Write the molecular formula for methylpropane. 5. Compound X has been found to contain twice as many hydrogen atoms as carbon atoms ond no other elements. a. Write the empirical formula for compound X. b. Of the molecular formulas in the box below, which ones could possibly represent compound X? 6. Compound Y has been found to contain elements in the following ratio: 3 carbon atoms : 6 hydrogen atoms : 1 oxygen atoms. a. Write the empirical formula for compound Y. b. Of the molecular formulas in the box below, which ones could possibly represent compound Y? CH 3 C 5 H 10 C 6 H 12 O 2 C 12 H 26 C 11 H 22 C 2 H 4 C 10 H 20 O 3 CH 4 C 4 H 6 CH 2 Page 1 of 1 3.3 w-1 formulas.docx
3-10 Identifying Reaction Types Determine if the following are synthesis (S), decomposition (D), single replacement (SR), or double replacement (DR) reactions. 1. 2NaClO 3 2NaCl + 3O 2 2. 2AgNO 3 + Ni Ni(NO 3 ) 2 + 2Ag 3. H 2 CO 3 H 2 O + CO 2 4. BaCO 3 BaO + CO 2 5. 4Cr + 3 O 2 2 Cr 2 O 3 6. Ca + 2HCl CaCl 2 + H 2 7. Ca(C 2 H 3 O 2 ) 2 + Na 2 CO 3 CaCO 3 + 2NaC 2 H 3 O 2 8. Cu(OH) 2 + 2HC 2 H 3 O 2 Cu(C 2 H 3 O 2 ) 2 + 2H 2 O 9. 8Cu + S 8 8CuS 10. P 4 + 5 O 2 2 P 2 O 5 11. 2K + 2H 2 O 2KOH + H 2 12. 3AgNO 3 + K 3 PO 4 Ag 3 PO 4 + 3KNO 3 13. H 2 + Cl 2 2HCl 14. NaOH + HCl NaCl + H 2 O 15. Fe 2 O 3 + H 2 O 2FeO + OH 16. 2NH 3 N 2 + 3H 2 17. Mg + H 2 SO 4 MgSO 4 + H 2 18. F 2 + 2HBr Br 2 + 2HF 19. Zn(NO 3 )2 + CaCO 3 Ca(NO 3 ) 2 + ZnCO 3 20. 4Al + 3O 2 2Al 2 O 3 Page 1 of 2 3.4 w-1 Identifying Reaction Types.docx
21. CuSO 4 5H 2 O CuO + H 2 SO 4 + 4H 2 O 3-11 22. SiF 6 + 6Xe SiXe 6 + 3F 2 23. H 2 + Cl 2 2HCl 24. NaOH + HCl NaCl + H 2 O 25. 2NH 3 N 2 + 3H 2 26. Mg + H 2 SO 4 MgSO 4 + H 2 27. Zn(NO 3 ) 2 + CaCO 3 Ca(NO 3 ) 2 + ZnCO 3 28. 4Al + 3O 2 2Al 2 O 3 29. CuSO 4 5H 2 O CuO + H 2 SO 4 + 4H 2 O 30. SiF 6 + 6Xe SiXe 6 + 3F 2 31. 2 NaClO 3 2 NaCl + 3 O 2 32. 2 AgNO 3 + Ni Ni(NO 3 ) 2 + 2 Ag 33. H 2 CO 3 H 2 O + CO 2 34. BaCO 3 BaO + CO 2 35. 4 Cr + 3 O 2 2 Cr 2 O 3 36. Ca + 2 HCl CaCl 2 + H 2 37. Ca(C 2 H 3 O 2 )2 + Na 2 CO 3 CaCO 3 + 2 NaC 2 H 3 O 2 38. Cu(OH) 2 + 2 HC 2 H 3 O 2 Cu(C 2 H 3 O 2 ) 2 + 2 H 2 O 39. P 4 + 5 O 2 2 P 2 O 5 40. 2 K + 2 H 2 O 2 KOH + H 2 41. 3 AgNO 3 + K 3 PO 4 Ag 3 PO 4 + 3 KNO 3 Page 2 of 2 3.4 w-1 Identifying Reaction Types.docx
Balancing Equations 1) C 2 H 4 O 2 + O 2 CO 2 + H 2 O 3-12 2) AgI + Fe 2 (CO 3 ) 3 FeI 3 + Ag 2 CO 3 3) V 2 O 5 + CaS CaO + V 2 S 5 4) NaNO 3 + PbO Pb(NO 3 ) 2 + Na 2 O 5) AgBr + GaPO 4 Ag 3 PO 4 + GaBr 3 6) H 2 SO 4 + B(OH) 3 B 2 (SO4) 3 + H 2 O Page 1 of 4 3.5 w-1 balancing equations.docx
3-13 7) S 8 + O 2 SO 2 8) Fe + AgNO 3 Fe(NO 3 ) 2 + Ag 9) Fe 2 O 3 + H 2 Fe + H 2 O 10) Li + N 2 Li 3 N 11) Zn + HCl ZnCl 2 + H 2 12) Mg + N 2 Mg 3 N 2 Page 2 of 4 3.5 w-1 balancing equations.docx
13) Ca 3 P 2 Ca + P 3-14 14) HCl + F 2 HF + Cl 2 15) NaCl Na + Cl2 16) H 2 O H 2 + O 2 17) N 2 + H 2 NH 3 18) Ag + AuCl 3 AgCl + Au Page 3 of 4 3.5 w-1 balancing equations.docx
3-15 19) Pb(NO 3 ) 2 + NaCl PbCl 2 + NaNO 3 20) Na 3 PO 4 + AgNO 3 Ag3PO 4 + NaNO 3 21) C 3 H 8 + O 2 CO 2 + H 2 O 22) CH 4 + O 2 CO 2 + H 2 O 23) H 2 + Cl 2 HCl 24) Na + H 2 O NaOH + H 2 Page 4 of 4 3.5 w-1 balancing equations.docx
3-16 Name Period Identifying Reaction Types Identify the reaction type and balance the following: Reaction Date Reaction Type 1. N 2 + H 2 NH 3 2. KClO 3 KCl + O 2 3. Zn + HCl ZnCl 2 + H 2 4. C 3 H 8 + O 2 CO 2 + H 2 O 5. NaCl + F 2 NaF + Cl 2 6. K 3 PO 4 + Al(NO 3 ) 3 KNO 3 + AlPO 4 7. H 2 + O 2 H 2 O 8. AgNO 3 + MgCl 2 AgCl + Mg(NO 3 ) 2 Page 1 of 2 3.5 w-2 balancing equations and reaction type.docx
3-17 9. CH 4 + O 2 CO 2 + H 2 O 10. AlBr 3 + K 2 SO 4 KBr + Al 2 (SO 4 ) 3 11. FeCl 3 + NaOH Fe(OH) 3 + NaCl 12. P + O 2 P 2 O 5 13. C 3 H 8 + O 2 CO 2 + H 2 O 14. S 8 + O 2 SO 3 15. K + MgBr 2 KBr + Mg 16. Na 2 CO 3 + Ca(OH) 2 NaOH + CaCO 3 Page 2 of 2 3.5 w-2 balancing equations and reaction type.docx
Calculate the formula mass for the following: Formula Mass 3-18 1) Br2 7) SO3 2) CsOH 8) HNO3 3) BaCl2 9) (NH4)2CO3 4) FeF3 10) Mg3(PO4)2 5) AlCl3 11) Pb(CH3COO)2 6) Al2O3 Page 1 of 1 3.6 w-1 Formula Mass.docx
3-19 Molar Mass GFM Find the gfm of the following compounds. 1) NaBr 8) (NH 4 ) 2 S 2) PbSO 4 9) Zn(C 2 H 3 O 2 ) 2 3) Ca(OH) 2 10) AgF 4) Na 3 PO 4 11) H 2 SO 4 5) (NH 4 ) 2 CO 3 12) NH 4 OH 6) C 6 H 12 O 6 13) Al 2 (SO 4 ) 3 7) Fe 3 (PO 4 ) 2 14) O 2 Page 1 of 5 3.7 w-1 Molar Mass and g-m m-g.docx
3-20 Convert the following from grams to moles: 1) 15.0 g C6H12O6 Convert the following from moles to grams: 1) 0.500 moles LiF 2) 25.0 g NaOH 2) 0.1188 moles NaOH 3) 54.0 g HCl 3) 4.00 moles KCl 4) 13.0 g H2O 4) 10.0 moles H2O2 5) 23.0 g Ca(NO3)2 5) 13.0 moles Na2CO3 6) 1.00 g H2SO4 6) 28.0 moles H2O 7) 0.105 g O2 7) 0.800 moles NH3 Page 2 of 5 3.7 w-1 Molar Mass and g-m m-g.docx
3-21 Grams, Molecules, and Moles Worksheet 1) How many molecules are there in 32.0 grams of FeF3? Molecules: 2) How many molecules are there in 250. grams of Na2SO4? Molecules: 3) How many grams are there in 4.60 x 1024 atoms of silver? Grams: 4) How many grams are there in 4.70 x 1023 molecules of AgNO3? Grams: 5) How many grams are there in 5.70 x 1023 molecules of H2SO4? Grams: 6) How many molecules are there in 221 grams of Cu(NO3)2? Molecules: Page 3 of 5 3.7 w-1 Molar Mass and g-m m-g.docx
7) How many grams are there in 4.90 x 1025 molecules of H2? Molecules: 3-22 8) How many molecules are there 230. grams of CoCl2? Molecules: 9) How many molecules are there in 3.20 grams of NH4SO2? Molecules: 10) How many grams are there in 4.40 x 1023 molecules of N2I6? Grams: 11) How many molecules are there in 120.0 grams of CCl4? Molecules: 12) How many molecules are there 4.39 grams of LiCl? Molecules: Page 4 of 5 3.7 w-1 Molar Mass and g-m m-g.docx
Solutions to the Molar Mass Practice Worksheet: 3-23 Important note to students: The mole is a unit commonly used to indicate a number of things about the amount of material present. I will be introducing it this week. All of the units given here are grams per mole, which may be abbreviated as g/mol, grams/mol, or g. mol -1, depending on how your teacher likes to see it written. They all mean the same thing, but it s probably a good idea to use whatever your teacher showed you in class. Also, remember that if you don t use units in your answer, the answer is wrong! All answers are rounded to the nearest 0.1 grams. 1) 102.9 g/mol 2) 303.3 g/mol 3) 74.1 g/mol 4) 164.0 g/mol 5) 96.0 g/mol 6) 180.0 g/mol 7) 357.4 g/mol 8) 68.1 g/mol 9) 183.4 g/mol 10) 126.9 g/mol Page 5 of 5 3.7 w-1 Molar Mass and g-m m-g.docx
Empirical Formula Worksheet Molecular formula from empirical formula and molecular mass. 3-24 Step 1 Write the empirical formula. Step 2 Calculate the empirical formula mass. Step 3 Write the molar mass. Step 4 Divide the empirical mass by the molar mass this is your multiplier. Step 5 Multiply empirical subscripts by your multiplier this is your molecular formula. Empirical Formula Empirical Formula Mass Molar Mass Multiplier Molecular Formula 1. A compound has an empirical formula of NO 2 and a molecular mass of 92. What is the molecular formula? 2. A compound with an empirical formula of CH 2 has a molecular mass of 70. What is the molecular formula? 3. A compound has an empirical formula of CH 2 and a molecular mass of 42. What is the molecular formula? Page 1 of 3 3.7 w-2 molecular mass from empirical.docx
4. A compound has an empirical formula of CH 4 N and a molar mass of 120. What is the molecular formula? 3-25 5. A compound has an empirical formula of NS and a molecular mass of 138. What is the molecular formula? 6. A compound has a molecular mass of 168 and an empirical formula of C 3 H 4 O. What is the molecular formula? 7. A compound has a molecular mass of 189 and an empirical formula of C 2 H 7 O 2. What is the molecular formula? Page 2 of 3 3.7 w-2 molecular mass from empirical.docx
8. A compound has a molecular mass of 222 and an empirical formula of Mn(C 2 H 4 ) 2. What is the molecular formula? 3-26 9. A compound has a molecular mass of 180 and an empirical formula of CH 2 O. What is the molecular formula? 10. A compound has a molecular mass of 78 and an empirical formula of CH. What is the molecular formula? 11. A compound has a molecular mass of 70 and an empirical formula of CH 2. What is the molecular formula? Page 3 of 3 3.7 w-2 molecular mass from empirical.docx
Percent Composition 3-27 Page 1 of 2 3.7 w-3 percent composition.docx
3-28 Page 2 of 2 3.7 w-3 percent composition.docx
Empirical Formula From Percent Composition 3-29 Determine the empirical formula for each of the following: 1. 92.24% C; 7.76% H 2. 36.48% Na; 25.44% S; 38.08% O 3. 49.99% C; 5.61% H; 44.40% O 4. 38.76% Ca; 19.97% P; 41.27% O 5. A compound composed of 0.556g carbon and 0.0933g hydrogen. Page 1 of 2 3.7 w-4 empirical formula from percent comp.docx
Molecular Formula from Empirical Formula and Percent Composition 3-30 1. Calculate the molecular formula for the following: a. empirical formula CH, molar mass = 78 g/mol b. empirical formula NO2, molar mass = 46.01 g/mol c. caffeine, 49.5% C, 5.15% H, 28.9% N, 16.5% O by mass, molar mass = 195 g d. A compound analyzes as 79.08% C; 5.54% H and 15.38% N. What isthe molecular formula if the molar mass is 273.36 g/mol? Page 2 of 2 3.7 w-4 empirical formula from percent comp.docx
Name 3-31 Crystal Hydrates Page 1 of 2 3.7 w-5 Crystal Hydrates.docx
3-32 Page 2 of 2 3.7 w-5 Crystal Hydrates.docx
Mole Ratio Worksheet 3-33 1) Given this equation: N 2 + 3 H 2 ---> 2 NH 3, write the following molar ratios: a) N 2 / H 2 b) N 2 / NH 3 c) H 2 / NH 3 2) Given the following equation: 8 H 2 + S 8 ---> 8 H 2 S, write the following molar ratios: a) H 2 / H 2 S b) H 2 / S 8 c) H 2 S / S 8 3) Answer the following questions for this equation: 2 H 2 + O 2 ---> 2 H 2 O a) What is the H 2 / H 2 O molar ratio? b) Suppose you had 20 moles of H 2 on hand and plenty of O 2, how many moles of H 2 O could you make? c) What is the O 2 / H 2 O molar ratio? d) Suppose you had 20 moles of O 2 and enough H 2, how many moles of H 2 O could you make? 4) Use this equation: N 2 + 3 H 2 ---> 2 NH 3, for the following problems a) If you used 1 mole of N 2, how many moles of NH 3 could be produced? b) If 10 moles of NH 3 were produced, how many moles of N 2 would be required? c) If 3.00 moles of H 2 were used, how many moles of NH 3 would be made? d) If 0.600 moles of NH 3 were produced, how many moles of H 2 are required? Page 1 of 3 3.8 w-1 Mole Ratio and Mol-Mol.docx
Mole/Mole Ratio Problems 3-34 1. N 2 + H 2 NH 3 a. How many moles of hydrogen are needed to completely react with two moles of nitrogen? b. How many moles of nitrogen trihydride can be produced with 5 moles of nitrogen? c. How many moles of nitrogen are needed to produce.5 moles of nitrogen trihydride? d. How many liters of nitrogen trihydride can be produced from 24 liters of nitrogen gas? 2. KClO 3 KCl + O 2 a. How many moles of oxygen are produced by the decomposition of six moles of potassium chlorate? b. How many moles of potassium chloride are produced by the decomposition of.75 moles of potassium chlorate? c. How many moles of potassium chlorate are needed to produce 100 moles of oxygen? d. How many liters of oxygen will the decomposition of 100 liters of potassium chlorate produce? Page 2 of 3 3.8 w-1 Mole Ratio and Mol-Mol.docx
3-35 3. Zn + HCl ZnCl 2 + H 2 a. How many moles of hydrogen are produced from the reaction of three moles of zinc? b. How many moles zinc are needed to produce 3.5 moles of zinc chloride? c. How many moles of hydrogen can 15 moles hydrogen chloride produce? d. How many liters hydrogen chloride are needed react with 11 liters of zinc? 4. C 3 H 8 + O 2 CO 2 + H 2 O a. How many moles of oxygen are necessary to react completely with fours moles of Propane (C3H8)? b. How many moles of Propane (C3H8) are needed to produce 25 moles of carbon dioxide? c. How many moles of water will 3 moles of propane (C3H8) produce? d. How many liters of Propane (C3H8) are needed to react with 75 liters of oxygen? 5. NaCl + F 2 NaF + Cl 2 a. How many moles of fluorine are needed to produce 3.2 moles of sodium chloride? b. How many moles of chlorine can me produced by using a total of 3 moles of sodium chloride? c. How many moles of sodium fluoride can five moles of fluorine produce? Page 3 of 3 3.8 w-1 Mole Ratio and Mol-Mol.docx
Name Date 3-36 Period Math of Chemistry Review Page 1 of 4 3.8 w- review.pub
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REGENTS CHEMISTRY Moles & Stoich Practice Test Name Mr. Dolgos Period 3-41 1) How many oxygen atoms are represented in the formula Al 2 (CO 3 ) 3? a) 3 b) 9 c) 10 d) 6 2) What is the total number of atoms present in 1 mole of Ca 3 (PO 4 ) 2? a) 8 b) 5 c) 10 d) 13 3) What is the total mass of iron in 1.0 mole of Fe 2 O 3? a) 72 g b) 112 g c) 56 g d) 160 g 4) What is the gram formula mass of Li 2 SO 4? a) 206 g b) 55 g c) 110 g d) 54 g 5) What is the percent composition by mass of sulfur in H 2 SO 4? [formula mass = 98] a) 98% b) 16% c) 65% d) 33% 6) A hydrate is a compound with water molecules incorporated into its crystal structure. In an experiment to find the percent by mass of water in a hydrated compound, the following data were recorded: Mass of test tube + hydrate crystals before heating Mass of test tube Mass of test tube + anhydrate crystals after heating 25.3 grams 21.3 grams 22.3 grams What is the percent by mass of water in the hydrate? a) 75% b) 50% c) 8.0% d) 95% 7) Which of the following statements explains why mass is lost when a student heats a sample of BaCl 2 2H 2 O crystals? a) water is given off as a gas c) chlorine is given off as a gas b) the crystals sublime d) the crystals fuse (melt) 8) When the equation H 2 S + O 2 H 2 O + SO 2 is completely balanced using the smallest whole numbers, the sum of all the coefficients is a) 9 b) 11 c) 7 d) 5
9) What is the percent by mass of water in the hydrate Na 2 CO 3 10H 2 O [formula mass = 286]? 3-42 a) 26.1% b) 62.9% c) 6.89% d) 214.5% 10) How many grams are there in 2.5 moles of C 2 H 5 OH? a) 18 b) 115 c) 46 d) 0.05 11) Which quantity is equivalent to 146 grams of NaCl? a) 1.0 mole b) 2.5 moles c) 2.0 moles d) 1.5 moles 12) The equation below is best classified as which type of chemical reaction? H 2 + Fe 3 O 4 --> Fe + H 2 O a) Synthesis b) Combustion c) Single replacement d) Double replacement 13) When the equation NaBr + H 3 PO 4 Na 3 PO 4 + HBr is balanced using the smallest whole numbers, the sum of the coefficients will be a) 6 b) 8 c) 5 d) 4 14) The equation below is best classified as which type of chemical reaction? 2C 2 H 2 + 5O 2 4CO 2 + 2H 2 O a) Synthesis b) Combustion c) Single replacement d) Double replacement 15) Given the reaction: 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O What is the ratio of moles of CO 2 produced to moles of C 2 H 6 consumed? a) 7 to 2 b) 2 to 1 c) 1 to 1 d) 3 to 2 16) Which represents the greatest mass of chlorine? a) 1 atom of chlorine b) 1 molecule of chlorine c) 1 mole of chlorine d) 1 gram of chlorine 17) Given the reaction: 2Na + 2H 2 O 2NaOH + H 2, what is the total number of moles of hydrogen produced when 4 moles of sodium react completely? a) 1 b) 2 c) 3 d) 4
18) What type of reaction best describes the following chemical reaction? 3-43 Zn + CuSO 4 --> ZnSO 4 + Cu a) single replacement c) decomposition b) double replacement d) synthesis 19) Which chemical equation best represent a decomposition reaction? a) Cl 2 + 2KI 2KCl + I 2 c) H 2 CO 3 H 2 O + CO 2 b) 2Al + 3Cl 2 2AlCl 3 d) KCl + AgNO 3 KNO 3 + AgCl 20) What is the molecular formula of a compound that has a molecular mass of 54 and an empirical formula of C 2 H 3? a) C 8 H 12 b) C 6 H 9 c) C 4 H 6 d) C 2 H 3 21) What is the empirical formula of the compound whose molecular formula is P 4 O 10? a) P 8 O 20 b) PO 2 c) P 2 O 5 d) PO 22) Which of the following is an empirical formula? a) H 2 O 2 b) H 2 O c) C 2 H 2 d) C 4 H 8 23) Which represents both an empirical and molecular formula? a) P 2 O 5 b) C 3 H 6 c) N 2 O 4 d) C 6 H 12 O 6 Constructed Response Questions For questions 24 and 25, show all work and express your answer in the appropriate units. 24) Calculate the gram formula mass of ZnSO 4. (3 pts) 25) Use your answer from 23 to calculate the percent by mass of zinc in ZnSO 4. (3 pts) 26) Balance the following reaction and reduce to the lowest whole number coefficients: (1 pt) H 2 SO 4 + B(OH) 3 B 2 (SO 4 ) 3 + H 2 O
27) Li and KNO3 according to the following equation: 3-44 Li + KNO 3 LiNO 3 + X Write the formula for the missing product X. (1 pt) Use the chemical equation below to answer questions 28-30. N 2 + H 2 NH 3 28) Balance the equation above using the lowest whole number coefficients. 29) How many moles of H 2 are required to produce 6.5 moles of NH 3? Show all work and make sure your answer has the correct number of significant figures and proper units. 30) How many grams of NH 3 are produced if 50.0 grams of N 2 are consumed? Show all work and make sure your answer has the correct number of significant figures and proper units. For question 31, show all work and make sure your answer has the correct number of significant figures and proper units. 31) A compound consists of 85% silver and 15% fluorine by mass. a) What is the empirical formula for this compound? b) What is the molecular formula (molar mass = 126.9g)
REGENTS CHEMISTRY Moles & Stoich Practice Test Name Mr. Dolgos Period For questions 24 and 25, show all work and express your answer in the appropriate units. 3-45 1. 2. 24) Calculate the gram formula mass of ZnSO 4. (3 pts) 3. 4. 5. 25) Use your answer from 23 to calculate the percent by mass of zinc in ZnSO 4. (3 pts) 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 26) Balance the following reaction using the lowest whole number coefficients: (1 pt) H 2 SO 4 + B(OH) 3 B 2 (SO 4 ) 3 + H 2 O 27) Li and KNO3 according to the following equation: Li + KNO 3 LiNO 3 + X Write the formula for the missing product X. (1 pt) N 2 + H 2 NH 3 28) Balance the equation above using the lowest whole number coefficients. 29) How many moles of H 2 are required to produce 6.5 moles of NH 3? Show all work and make sure your answer has the correct number of significant figures and proper units. 30) How many grams of NH 3 are produced if 50.0 grams of N 2 are consumed? Show all work and make sure your answer has the correct number of significant figures and proper units. 22. 23. 31) A compound consists of 85% silver and 15% fluorine by mass (molar mass = 126.9g). a) What is the empirical formula for this compound? b) What is the molecular formula?