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Exam 4: The Mole and Stoichiometry

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Question 21

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How many grams of water could be made from 5.0 mol H₂ and 3.0 mol O₂?

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Question 22

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There are ________ sulfur atoms in 25.6 g of Al₂(S₂O₃)₃. Hint: You can't convert directly from mass of a compound to atoms of an element. Use an intermediary.

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Question 23

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In a chemical equation, C₃H₆O₂ + PCl₃ $\rarr$ C₃H₅OCl + H₃PO₃, when the reaction was carried out, the actual yield of C₃H₅OCl was calculated as 97.3 % of the theoretical value. If the theoretical yield should have been 1.42 moles, how many grams of C₃H₅OCl were actually obtained?

A sample of Ni(CO) ₄, a toxic transition-metal complex, has 5.23 × 10²⁴ atoms of carbon. How many atoms of Ni does it contain?

The atomic mass of aluminum is 26.982 u. How many aluminum atoms are in a 4.55 g sample of aluminum?

Given the chemical equation, 2Mg + O₂ → 2MgO, when 2.2 g Mg react with 3.6 g of O₂, 2.7 g MgO were obtained. What is the percent yield in the reaction?

A compound contains potassium, sulfur, and oxygen. The composition of the compound is: potassium, 49.410%; sulfur, 20.261%. Determine the empirical formula of the compound. Hint: Assume you have 100 grams of this substance and use moles to relate the mass of one element to another.

The reactants and products in a reaction are shown below in the unbalanced chemical equation: P₄O₁₀ + Ca(OH) ₂ $\rarr$ Ca₃(PO₄) ₂ + H₂O If you start with 2.40 moles of P₄O₁₀ and 3.30 moles of Ca(OH) ₂ and all of the limiting reactant is consumed, Hint: You must balance the equation first.

In the course of determination of a chemical formula, a student obtained the following mole ratios: .The empirical formula for the compound is ________.

The Hall process for the production of aluminum involves the reaction of aluminum oxide with elemental carbon to give aluminum metal and carbon monoxide. If the yield of this reaction is 82% and aluminum ore is 71% by mass aluminum oxide, what mass of aluminum ore must be mined in order to produce 1.0 × 10³ kg (1 metric ton)of aluminum metal by the Hall process? Hint: You need to first determine how product you need to aim for to accommodate an actual yield of 82%, and then account for the fact that the ore is only 71% aluminum oxide.

The atomic mass of helium is 4.0026 u. What is the mass of a helium sample that contains 0.427 moles of He gas?

You are given the balanced equation: C₄H₄ + 5 O₂ $\rarr$ 4 CO₂ + 2 H₂O If 0.3618 moles of C₄H₄ are allowed to react with 1.818 moles of O₂, and this is the only reaction which occurs, what is the maximum quantity of carbon dioxide that could be produced?

What is the expected yield of Pb, if 25.0 g C react with 25.0 g of PbO according to the chemical equation, PbO + C → CO + Pb?

A 6.987 g sample of a hydrocarbon, upon combustion analysis, yielded 8.398 grams of carbon dioxide. What is the percent, by mass, of carbon in the hydrocarbon?

A compound has an empirical formula of CH₂O. An independent analysis gave a value of 150.13 g for its molar mass. What is the molecular formula of the compound?

A mole of oxygen, O₂, and a mole of ozone, O₃, contain the same number of molecules.

A laboratory unknown is a mixture of calcium carbonate and magnesium carbonate. These substances decompose to form calcium oxide and magnesium oxide, respectively, when heated at a high temperature for a prolonged period. A sample of this laboratory unknown mixture with a mass of 5.424 grams was decomposed by heating for several hours at 950 ^°C. The oxide residue produced had a mass of 2.791 grams. From this laboratory data calculate the percent, by weight, of calcium carbonate in the unknown. Hint: Use the balanced chemical equations to find the molar ratios of the carbonates to the oxides, then create two algebraic equations - one for the carbonates and the other for the products. This will give you two equations with two unknowns, which can be solved to determine the number of moles of one of your substances.

A freshly prepared compound contains potassium, hydrogen, phosphorus, and oxygen. The composition of the compound is: potassium, 44.895%; hydrogen, 0.5787%; phosphorus, 17.783%. Determine the empirical formula of the compound. Hint: Assume you have 100 grams of this substance and use moles to relate the mass of one element to another.

The mass of 3.00 moles of phosphorus (P₄), is ________ grams.

What is the percent, by mass, of calcium in Ca(OCl) ₂?