Ch.10 - Gases

Problem 120b

Chapter 10, Problem 120b

An herbicide is found to contain only C, H, N, and Cl. The complete combustion of a 100.0-mg sample of the herbicide in excess oxygen produces 83.16 mL of CO2 and 73.30 mL of H2O vapor expressed at STP. A separate analysis shows that the sample also contains 16.44 mg of Cl. (b) Calculate its empirical formula.

Verified step by step guidance

Determine the moles of CO2 and H2O produced. Use the ideal gas law or molar volume at STP (22.4 L/mol) to convert the volumes of CO2 and H2O to moles.

Calculate the moles of carbon from the moles of CO2 produced, assuming each mole of CO2 contains one mole of carbon.

Calculate the moles of hydrogen from the moles of H2O produced, assuming each mole of H2O contains two moles of hydrogen.

Calculate the mass of carbon and hydrogen using their respective molar masses. Subtract the masses of carbon, hydrogen, and chlorine from the total mass of the sample to find the mass of nitrogen.

Convert the masses of carbon, hydrogen, nitrogen, and chlorine to moles using their respective molar masses. Then, find the simplest whole number ratio of these elements to determine the empirical formula.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.

Video duration:

13m

Was this helpful?

Key Concepts

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

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. It is determined by analyzing the mass of each element present in a sample and converting these masses into moles. The resulting mole ratios are then simplified to the smallest integers, providing a basic understanding of the compound's composition.

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, which is essential for determining the empirical formula from combustion data, as it involves converting volumes of gases to moles using the ideal gas law.

Combustion Analysis

Combustion analysis is a technique used to determine the elemental composition of organic compounds. In this process, a sample is burned in excess oxygen, and the products (typically CO2 and H2O) are measured. The volumes of these gases produced can be used to calculate the amounts of carbon and hydrogen in the original sample, which are crucial for deriving the empirical formula.

Recommended video:

Guided course

01:29

Combustion of Non-Hydrocarbons

Related Practice

Textbook Question

Cyclopropane, a gas used with oxygen as a general anesthetic, is composed of 85.7% C and 14.3% H by mass. (a) If 1.56 g of cyclopropane has a volume of 1.00 L at 99.7 kPa and 50.0 °C, what is the molecular formula of cyclopropane?

1379

views

Textbook Question

Cyclopropane, a gas used with oxygen as a general anesthetic, is composed of 85.7% C and 14.3% H by mass. (b) Judging from its molecular formula, would you expect cyclopropane to deviate more or less than Ar from ideal-gas behavior at moderately high pressures and room temperature? Explain.

Open Question

Consider the combustion reaction between 1.00 L of liquid methanol (density = 0.850 g/mL) and 500 L of oxygen gas measured at STP. The products of the reaction are CO2(g) and H2O(g). Calculate the volume of liquid H2O formed if the reaction goes to completion and you condense the water vapor.

Textbook Question

An herbicide is found to contain only C, H, N, and Cl. The complete combustion of a 100.0-mg sample of the herbicide in excess oxygen produces 83.16 mL of CO₂ and 73.30 mL of H₂O vapor expressed at STP. A separate analysis shows that the sample also contains 16.44 mg of Cl. (c) What other information would you need to know about this compound to calculate its true molecular formula?

677

views

Textbook Question

A 4.00-g sample of a mixture of CaO and BaO is placed in a 1.00-L vessel containing CO₂ gas at a pressure of 97.33 kPa and a temperature of 25 °C. The CO₂ reacts with the CaO and BaO, forming CaCO₃ and BaCO₃. When the reaction is complete, the pressure of the remaining CO₂ is 20.0 kPa. (a) Calculate the number of moles of CO₂ that have reacted. (b) Calculate the mass percentage of CaO in the mixture.

1180

views

Textbook Question

Ammonia and hydrogen chloride react to form solid ammonium chloride: NH31g2 + HCl1g2¡NH4Cl1s2 Two 2.00-L flasks at 25 °C are connected by a valve, as shown in the drawing. One flask contains 5.00 g of NH31g2, and the other contains 5.00 g of HCl(g). When the valve is opened, the gases react until one is completely consumed. (a) Which gas will remain in the system after the reaction is complete?

882

views