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Exam 2: The Mole

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Question 1

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How many moles of Na₂S are found in 20.0 grams of sodium sulfide, Na₂S?

A) 0.256 moles
B) 0.364 moles
C) 2.75 moles
D) 3.90 moles
E) none of these

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Question 2

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Calculate the % mass of sodium in sodium sulfate, Na₂SO₄.

A) 16%
B) 23%
C) 32%
D) 54%
E) 67%

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Question 3

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Apatite is a mineral that is found in tooth enamel. When fluoride toothpastes are used, this mineral is converted to fluoroapatite, which is much harder and therefore more resistant to decay. What is the percent by weight of fluorine in fluoroapatite, Ca₅(PO₄) ₃F?

Determine the number of moles in 12.5 g of carbon tetrachloride, CCl₄.

How many grams of CO₂ gas are produced from the combustion of 10.0 grams of isooctane? 2 C₈H₁₈ + 25 O₂ $\rightarrow$ 16 CO₂ + 18 H₂O

A 2.50 g sample of a bronze gong was cut out and dissolved in sulfuric acid. The copper sulfate produced was mixed with KI to form CuI and the triiodide ion, I₃^-. The I₃^- ion was then titrated with thiosulfate, S₂O₃^2-. Cu(s) + 2 H₂SO₄(aq) $\rightarrow$ CuSO₄(aq) + SO₂(g) + 2 H₂O(l) 2 CuSO₄(aq) + 5 I^-(aq) $\rightarrow$ 2 CuI(s) + I₃^-(aq) + 2 SO₄^2-(aq) I₃^-(aq) + 2 S₂O₃^2-(aq) → 3 I^-(aq) + S₄O₆^2-(aq) If it took 31.5 mL of 1.00 M thiosulfate for this titration, how many moles of copper were present in the original 2.50 g sample?

How many grams of NaNO₃ are required to prepare 2.00 L of a 0.250 M NaNO₃ solution?

If adding 22.7 mL of 0.6 M HCl to 1.00 L of a solution of AgNO₃ precipitated 1.95 g of AgCl, what was the concentration of the original AgNO₃ solution? AgNO₃(aq) + HCl(aq) $\rightarrow$ AgCl(s) + HNO₃(aq)

Ethyl alcohol, C₂H₅OH, is also known as drinking alcohol. It can be produced by the fermentation of glucose by the following reaction. C₆H₁₂O₆(aq) $\rightarrow$ 2 C₂H₅OH(aq) + 2 CO₂(g) How many $\textbf{ moles }$ of ethanol can be produced from $\textbf{ 100 g }$ of glucose?

One way of determining blood alcohol levels is by titrating a sample of blood according to the following net ionic equation. C₂H₅OH(aq) + 2 Cr₂O₇^2-(aq) + 16 H⁺(aq) $\rightarrow$ 2 CO₂(g) + 4 Cr³⁺(aq) + 11 H₂O(l) If 8.76 mL of 0.04988 M Cr₂O₇^2- is required for the titration of a 10.00 mL sample of blood, what was the molarity of the alcohol present in the blood sample?

How much HgS forms when 113 mL of a 0.75 M CaS solution is mixed with 52 mL of a 1.21 M Hg(NO₃) ₂ solution?

In March of 2007 a number of pets were sickened or killed by pet food contaminated with the chemical melamine which is used in the manufacture of certain plastics. It is thought that the melamine was added to make a pet food additive appear to have more protein than it really did. Protein content is determined by measuring nitrogen content of food since protein is the main source of nitrogen in food. What is the % by mass of nitrogen in melamine which has the formula C₃H₆N₆?

What would happen to the amount of HCl produced in the previous question if the amount of H₂ is doubled?

The following four are based on the diagram above which describes the following lab procedure. Ten mL of an initial solution is pipetted into a volumetric flask. The 10.00 mL of initial solution is diluted to 100.0 mL with solvent to form the stock solution. Twenty five mL of the stock solution is then pipetted into another 100.0 mL volumetric flask and diluted to the 100.0 mL mark to form the final solution. The glassware in the diagram has been labeled with letters. -Which of the following statements correctly describes the relationship between moles of solute in the labeled containers?

The thermal decomposition of carbonates leads to the loss of CO₂. The decomposition of an unknown carbonate leads to a 35.1% weight loss. The unknown was which of the following compounds.

Acetylene gas, C₂H₂, burns in the presence of oxygen by the following reaction: 2 C₂H₂(g) + 5 O₂(g) $\rightarrow$ 2 H₂O(l) + 4 CO₂(g) If 4.5 moles of acetylene gas are to be burned, how many moles of oxygen will be required for the complete reaction of the acetylene?

When glucose reacts with oxygen in living systems, carbon dioxide and water are produced, and a great deal of energy is liberated. C₆H₁₂O₆(s) + 6 O₂(g) $\rightarrow$ 6 CO₂(g) + 6 H₂O(g) What weight of carbon dioxide can be produced from the reaction of 10.0 grams of glucose with 10.0 grams of oxygen?

The first silver dollar minted in the Americas was 3.95 cm in diameter and contained 27.07 grams of silver. If the density of silver is 10.5 g/cm³, what was the height of each coin?

The density of water in pounds per cubic foot is 62.4 lb/ft³. If a 2 ft³ bag of mulch sold at the local lawn care center weighs 30 lbs, which of the following correctly describes what happens when this mulch is poured on water?

A mixed oxide of potassium and vanadium is 28.3% by weight potassium and 37.0% by weight vanadium. What is the empirical formula?