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Exam 3: Stoichiometry of Formulas and Equations

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Question 51

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Magnesium fluoride is used in the ceramics and glass industry. What is the mass of 1.72 mol of magnesium fluoride?

A) 43.3 g
B) 62.3 g
C) 74.5 g
D) 92.9 g
E) 107 g

F) A) and C)
G) A) and D)

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Question 52

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The iodine "clock reaction" involves the following sequence of reactions occurring in a reaction mixture in a single beaker. 1. IO₃¯(aq) + 5I¯(aq) + 6H⁺(aq) $\rightarrow$ 3I₂(aq) + 3H₂O(l) 2. I₂(aq) + 2S₂O₃²¯(aq) $\rightarrow$ 2I¯(aq) + S₄O₆²¯(aq) The molecular iodine (I₂) formed in reaction 1 is immediately used up in reaction 2, so that no iodine accumulates. In one experiment, a student made up a reaction mixture which initially contained 0.0020 mol of iodate ions (IO₃¯) . If the iodate ions reacted completely, how many moles of thiosulfate ions (S₂O₃²¯) were needed in reaction 2, in order to react completely with the iodine (I₂) produced in reaction 1?

A) 0.0020 mol
B) 0.0030 mol
C) 0.0040 mol
D) 0.0050 mol
E) 0.0060 mol

F) None of the above
G) A) and D)

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Question 53

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In a correctly balanced equation, the number of reactant molecules must equal the number of product molecules.

In combustion analysis, the carbon and hydrogen contents of a substance are determined from the CO₂ and H₂O, respectively, which are collected in the absorbers.

Potassium dichromate, K₂Cr₂O₇, is used in tanning leather, decorating porcelain and water proofing fabrics. Calculate the number of chromium atoms in 78.82 g of K₂Cr₂O₇.

Calculate the molar mass of rubidium carbonate, Rb₂CO₃.

Terephthalic acid, used in the production of polyester fibers and films, is composed of carbon, hydrogen, and oxygen. When 0.6943 g of terephthalic acid was subjected to combustion analysis it produced 1.471 g CO₂ and 0.226 g H₂O. If its molar mass is between 158 and 167 g/mol, what is its molecular formula?

Alkanes are compounds of carbon and hydrogen with the general formula C_nH_2n+2. An alkane component of gasoline has a molar mass of between 125 and 130 g/mol. What is the value of n for this alkane?

Calculate the molar mass of tetraphosphorus decaoxide, P₄O₁₀, a corrosive substance which can be used as a drying agent.

How many milliliters of 1.58 M HCl are needed to react completely with 23.2 g of NaHCO₃ (? = 84.02 g/mol) ? HCl(aq) + NaHCO₃(s) $\rightarrow$ NaCl(s) + H₂O(l) + CO₂(g)

How many grams of sodium fluoride (used in water fluoridation and manufacture of insecticides) are needed to form 485 g of sulfur tetrafluoride? 3SCl₂(l) + 4NaF(s) $\rightarrow$ SF₄(g) + S₂Cl₂(l) + 4NaCl(s)

A compound consisting of C, H and O only, has a molar mass of 331.5 g/mol. Combustion of 0.1000 g of this compound caused a 0.2921 g increase in the mass of the CO₂ absorber and a 0.0951 g increase in the mass of the H₂O absorber. What is the empirical formula of the compound?

What volume, in L, of 10.0 M HCl is needed to make 2.00 L of 2.00 M HCl solution by dilution with water?

Calculate the molar mass of (NH₄) ₃AsO₄.

Aluminum reacts with oxygen to produce aluminum oxide which can be used as an adsorbent, desiccant or catalyst for organic reactions. 4Al(s) + 3O₂(g) $\rightarrow$ 2Al₂O₃(s) A mixture of 82.49 g of aluminum (? = 26.98 g/mol) and 117.65 g of oxygen (? = 32.00 g/mol) is allowed to react. Identify the limiting reactant and determine the mass of the excess reactant present in the vessel when the reaction is complete.

A single atom of hydrogen has a mass of 1.0 amu, while a mole of hydrogen atoms has a mass of 1.0 g. Select the correct conversion factor between atomic mass units and grams.