Question 1

Which of the following best describes the empirical formula of a compound?

Accepted Answer

The simplest whole-number molar ratio of elements in a compound.

Question 2

Glucose has the molecular formula $$C_6H_{12}O_6$. What is its empirical formula?

Accepted Answer

$$CH_2O$$

Question 3

A compound contains 25.6% Mg and 74.4% Cl by mass. What is its empirical formula? (Molar masses: Mg = 24.3 g/mol, Cl = 35.5 g/mol)

Accepted Answer

$$MgCl_2$$

Question 4

Which of the following statements is TRUE regarding empirical and molecular formulas?

Accepted Answer

The molecular formula is always a multiple of the empirical formula.

Question 5

A hydrocarbon is combusted and produces 44 g of $$CO_2$$ and 18 g of $$H_2O. $$What is the empirical formula of the hydrocarbon?

Accepted Answer

$$CH_3$$

Question 6

A compound has an empirical formula of $$CH_2Cl$$ and a molar mass of 99.0 g/mol. What is its molecular formula? (Empirical formula mass = 49.5 g/mol)

Accepted Answer

$$C_2H_4Cl_2$$

Question 7

Which of the following is the correct balanced equation for the combustion of methane ($$CH_4$$)?

Accepted Answer

$$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$

Question 8

A sample contains 79.85% Cu and 20.15% S by mass. What is the empirical formula of this mineral? (Cu = 63.55 g/mol, S = 32.07 g/mol)

Accepted Answer

$$Cu_2S$$

Question 9

Which of the following best describes the process of determining an empirical formula from mass percent data?

Accepted Answer

Convert mass percent to grams, then to moles, find the simplest whole number ratio.

Question 10

A compound is found to contain 24.3% C, 4.1% H, and 71.6% Cl by mass. What is its empirical formula? (C = 12.0 g/mol, H = 1.0 g/mol, Cl = 35.5 g/mol)

Accepted Answer

$$CH_2Cl$$

Question 11

Which instrument is commonly used to determine the molar mass of a compound by separating ions based on their mass-to-charge ratio?

Accepted Answer

Mass spectrometer

Question 12

Which law is obeyed when balancing chemical equations?

Accepted Answer

Law of Conservation of Mass

Question 13

Which of the following is the correct sequence for determining an empirical formula from mass percent data?

Accepted Answer

Convert mass percent to grams, convert grams to moles, divide by smallest number of moles, write formula.

Question 14

Which of the following is a correct statement about combustion reactions of hydrocarbons?

Accepted Answer

They always produce $$CO_2$$ and $$H_2O$$

Question 15

Balance the following combustion reaction: $$C_4H_{10} + O_2$ \rightarrow CO_2$ + H_2O$$

Accepted Answer

$$2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O$$

Empirical and Molecular Formulas & Chemical Reactions: Study Guide

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