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Ch.3 - Mass Relationships in Chemical Reactions
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.3 - Mass Relationships in Chemical ReactionsProblem 111
Chapter 3, Problem 111

Compound X contains only carbon, hydrogen, nitrogen, and chlorine. When 1.00 g of X is dissolved in water and allowed to react with excess silver nitrate, AgNO3, all the chlorine in X reacts and 1.95 g of solid AgCl is formed. When 1.00 g of X undergoes complete combustion, 0.900 g of CO2 and 0.735 g of H2O are formed. What is the empirical formula of X?

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Step 1: Determine the amount of chlorine in the compound. The molar mass of AgCl is 143.32 g/mol. Use the mass of AgCl formed to calculate the moles of AgCl, which is equal to the moles of Cl in the compound since AgNO3 reacts with Cl in a 1:1 ratio.
Step 2: Convert the moles of Cl to grams using the molar mass of Cl (35.45 g/mol). This gives the mass of Cl in the 1.00 g of compound X.
Step 3: Determine the amount of carbon and hydrogen in the compound. The molar mass of CO2 is 44.01 g/mol and the molar mass of H2O is 18.02 g/mol. Use the masses of CO2 and H2O formed to calculate the moles of CO2 and H2O. The moles of C in the compound is equal to the moles of CO2 since each CO2 molecule contains one C atom. The moles of H in the compound is twice the moles of H2O since each H2O molecule contains two H atoms.
Step 4: Convert the moles of C and H to grams using their molar masses (C: 12.01 g/mol, H: 1.01 g/mol). This gives the masses of C and H in the 1.00 g of compound X.
Step 5: The mass of nitrogen in the compound can be found by subtracting the masses of C, H, and Cl from the total mass of the compound (1.00 g). Convert this mass to moles using the molar mass of N (14.01 g/mol).
Step 6: Now you have the moles of C, H, Cl, and N in the compound. Divide each of these by the smallest value to get the ratio of the atoms, which gives the empirical formula.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It allows chemists to calculate the amounts of substances consumed and produced in a reaction, based on balanced chemical equations. In this question, stoichiometry is essential for determining the moles of chlorine that reacted with silver nitrate and the moles of carbon and hydrogen produced during combustion.
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Empirical Formula

The empirical formula of a compound represents the simplest whole-number ratio of the elements present in that compound. It is derived from the mass of each element in a sample and is crucial for understanding the composition of the compound. In this question, calculating the empirical formula involves determining the moles of carbon, hydrogen, nitrogen, and chlorine from the experimental data provided.
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Combustion Analysis

Combustion analysis is a method used to determine the elemental composition of organic compounds by burning the sample and measuring the resulting products, typically carbon dioxide and water. The masses of these products are used to calculate the amounts of carbon and hydrogen in the original compound. In this question, the combustion of compound X provides critical data needed to find the empirical formula by allowing the calculation of the moles of carbon and hydrogen present.
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