```Moles and Stoichiometry
Regent Review
 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
 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
 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
 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)
 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
 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
What is the percent by mass of oxygen in Fe2O3
(formula mass = 160)?
 16%
 30.%
 56%
 70.%
What is the correct formula for chromium (III) oxide?
 CrO3
 Cr3O
 Cr2O3
 Cr3O2
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%
 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
 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
 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)
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