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Moles and Stoichiometry Regent Review Correct Answer 0.5 moles Correct Answer is 6 Correct Answer is (3) C4H8 Correct Answer is (2) 1:2 (4) 310 g/mol is the correct answer Moles = grams/ molar mass 20 grams/ 85 (g/mol) = .235 moles (molar mass of carbon is 12 g/mol) (molar mass of Na2CO3 is 106 g/mol) (3) is the correct answer. In equation 3, there are the same number of atoms on each side of the equation. (Six atoms in the products and six atoms in the reactants.) Correct answer: 2 NaN3(s) → 2 Na(s) + 3 N2(g) 36 Which formula is both a molecular and an empirical formula? (1) C6H12O6 (3) C3H8O (2) C2H4O2 (4) C4H8 Correct answer 3 Empirical is fully reduced to the simplest whole number ratio 10 The sum of the atomic masses of the atoms in one molecule of C3H6Br2 is called the (1) formula mass (2) isotopic mass (3) percent abundance (4) percent composition Correct Answer 1 formula mass=mass of the formula 39 Which balanced equation represents a single replacement reaction? (1) Mg + 2AgNO3 → Mg(NO3)2+ 2Ag (2) 2Mg + O2 → 2MgO (3) MgCO3 → MgO + CO2 (4) MgCl2+ 2AgNO3 → 2AgCl + Mg(NO3)2 Correct Answer 1 A+BC-->AC + B 35 Which equation represents a decomposition reaction? (1) CaCO3(s) ==>CaO(s) + CO2(g) (2) Cu(s) + 2AgNO3(aq) ==>2Ag(s) + Cu(NO3)2(aq) (3) 2H2(g) + O2(g) ==>2H2O(l) (4) KOH(aq) + HCl(aq) ==>KCl(aq) + H2O(l) Correct Answer 1 decomp AB==> A + B 36 A compound has the empirical formula CH2O and a gramformula mass of 60. grams per mole. What is the molecular formula of this compound? (1) CH2O (3) C3H8O (2) C2H4O2 (4) C4H8O4 Correct Answer is 2 Given the equation: __FeCl2 + __Na2CO3 → __FeCO3 + __NaCl When the equation is correctly balanced using the smallest whole numbers, the coefficient of NaCl is 6 2 3 4 Correct Answer is 2 What is the percent by mass of oxygen in Fe2O3 (formula mass = 160)? 16% 30.% 56% 70.% Correct Answer is 30% What is the correct formula for chromium (III) oxide? CrO3 Cr3O Cr2O3 Cr3O2 Correct Answer is Cr2O3 A hydrated salt is a solid that includes water molecules within its crystal structure. A student heated a 9.10-gram sample of a hydrated salt to a constant mass of 5.41 grams. What percent by mass of water did the salt contain? 3.69% 16.8% 40.5% 59.5% Correct answer is 40.5% Gypsum is a mineral that is used in the construction industry to make drywall (sheetrock). The chemical formula for this hydrated compound is CaSO4• 2 H2O. A hydrated compound contains water molecules within its crystalline structure. Gypsum contains 2 moles of water for each 1 mole of calcium sulfate. What is the gram formula mass of CaSO4• 2 H2O? Round your answer to the nearest whole number. Answer: 172 or 172.2 grams Gypsum is a mineral that is used in the construction industry to make drywall (sheetrock). The chemical formula for this hydrated compound is CaSO4• 2 H2O. A hydrated compound contains water molecules within its crystalline structure. Gypsum contains 2 moles of water for each 1 mole of calcium sulfate. Calculate the percent composition by mass of water in this compound. Round your answer to the nearest percent. Answer: 21 or 20.9 or 20.93 % Which pair of formulas correctly represents a molecular formula and its corresponding empirical formula? C2H2 and CH C3H4 and CH2 C4H6 and CH C5H8 and C2H2 Correct Answer is C2H2 and CH Correct answer: 781 g Na3PO4 Correct answer: (2) 48.5 g Correct answer: (3) HClO3 (gram-formula mass = 84 g/mol)