Laws of Definite and Multiple Proportions

Quantitative

Objectives  Using the law of definite proportions, calculate the percent by mass for elements in a compound given the mass of each element in the compound. (Exploration 1)  Determine the mass of each element in a compound given the mass of the compound and the percent by mass for each element in the compound. (Exploration 1)  Evaluate the mass ratios for elements in a compound using the law of multiple proportions. (Exploration 2)

Description of Activity In Exploration 1, calculate the percent by mass for each element in a compound of a known mass. Use these percent by mass values to determine the proportion of elements in a different mass of the same compound according to the law of definite proportions. You will also practice calculating the mass of elements in compounds given the percent by mass values. In Exploration 2, calculate the mass ratios of selected compounds and then compare those two mass ratios according to the law of multiple proportions.

Jump Start 1. Define element and compound. 2. Explain how percent by mass is determined. 3. Describe the law of definite proportions. 4. Describe the law of multiple proportions.

Chemistry 1 Quantitative

Exploration 1: Law of Definite Proportions Procedure 1. In Exploration 1, select Water from the list of compounds. 2. Enter the mass of water provided in Table 1 by adjusting the slider or entering the value in the textbox. Select Submit. 3. The mass of each element in the compound will be displayed. Record these masses in Table 1. From this data, calculate the percent by mass for each element in the compound. Enter these percentages in the appropriate field and select Continue. The simulation will indicate whether your percent by mass values are correct or incorrect. Record the percent by mass for each element in Table 1. 4. When your percent by mass values are correct, a mass of the compound between 10.0 g and 99.9 g will be displayed. Record this mass in Table 2. Using your calculations of percent by mass, calculate the mass of each element for each compound, and record these values in Table 2. The simulation will indicate whether your masses of each element are correct or incorrect. 5. Select Restart and repeat steps 1–4 for the remaining compounds in Tables 1 and 2.

Observations and Analysis Table 1 Compound Mass of Mass of Percent by Compound (g) Elements in Mass of Compound (g) Elements in Compound (%)

Water (H2O) 25.0

Carbon 85.2 monoxide (CO)

Dinitrogen 50.0 trioxide (N2O3)

Ethane (C2H6) 39.8

Copper(II) 99.9 chloride (CuCl2)

Table 2

Compound Mass (g) Mass of Elements in Compound (g)

Water (H2O)

Carbon monoxide (CO)

Dinitrogen trioxide (N2O3)

Ethane (C2H6)

Copper(II) chloride (CuCl2)

1. How is the mass of a compound related to the masses of the elements that make up that compound? 2. How can you determine whether your percent by mass calculations are correct? 3. Show your calculation for the percent by mass of nitrogen and oxygen in dinitrogen trioxide (N2O3). Check your work. 4. Show your calculation for the mass of nitrogen and oxygen in dinitrogen trioxide based on the mass provided by the simulation. Check your work.

Exploration 2: Law of Multiple Proportions Procedure

1. Select Exploration 2. Choose Water and Hydrogen peroxide from the list of compounds. Select Submit. 2. The mass of each element in 75.0 g of water and 75.0 g of hydrogen peroxide will be displayed. From this data, calculate and enter the ratio of the masses of hydrogen to oxygen for water and hydrogen peroxide. Record the mass ratios in Table 3. The simulation will indicate whether your mass ratio values are correct or incorrect. Enter these values in the Mass ratio text boxes provided. 3. Compare the ratio of the mass of oxygen to hydrogen in water and the ratio of mass of oxygen to hydrogen in hydrogen peroxide. To determine the final comparison of mass ratios, divide each mass ratio by the smallest mass ratio value. For example, divide the mass ratio of hydrogen peroxide by the mass ratio of water and the mass ratio of water by the mass ratio of water to obtain small, whole numbers. If small whole numbers are not obtained, you must multiply everything by a whole number until you obtain the smallest possible whole number. Record the final comparison of ratios in Table 3. The simulation will indicate whether your ratio comparisons are correct or incorrect. Enter the Comparison of mass ratio in the text box provided. 4. Select Submit to verify your answers. 5. Repeat steps 1–4 for the groups of compounds given below: a. nitrogen monoxide and nitrogen dioxide b. hexane and hexyne c. copper(I) chloride and copper(II) chloride d. chromium(II) chloride and chromium(III) chloride

Observations and Analysis Table 3

Compound Mass Ratio Final Comparison of Mass Ratios

Water (H2O) mass of O H2O:H2O2 = = mass of H

Hydrogen peroxide (H2O2) mass of O = mass of H

Nitrogen monoxide (NO) mass of O NO:NO2 = = mass of N

Nitrogen dioxide (NO2) mass of O = mass of N

Hexane (C6H14) mass of C C6H14:C6H10 = = mass of H

Hexyne (C6H10) mass of C = mass of H

Copper(I) chloride (CuCl) mass of Cu CuCl:CuCl2 = = mass of Cl

Copper(II) chloride (CuCl2) mass of Cu = mass of Cl

Chromium(II) chloride mass of Cr CrCl2:CrCl3 = = (CrCl2) mass of Cl

Chromium(III) chloride mass of Cr = (CrCl3) mass of Cl

1. Describe what to do mathematically when the ratios are fractions. 2. Complete Table 4.

Table 4

Compound Mass Ratio Final Comparison of Ratios

Carbon monoxide (CO) mass of O CO:CO2 = = 1.33 mass of C

Carbon dioxide (CO2) mass of O = 2.66 mass of C

Dinitrogen monoxide (N2O) mass of N N2O:N2O3 = = 1.75 mass of O

Dinitrogen trioxide (N2O3) mass of N = 0.584 mass of O

Ethane (C2H6) mass of C C2H6:C2H2 = = 3.97 mass of H

Ethyne (C2H2) mass of C = 11.9 mass of H

Hexane (C6H14) mass of C C6H14:C6H10 = = 5.10 mass of H

2,4-hexadiene (C6H10) mass of C = 7.15 mass of H

Hexane (C6H14) mass of C C6H14:C6H12 = = 5.10 mass of H

Hexene (C6H12) mass of C = 5.94 mass of H

Conclusions Summarize what you learned about the laws of definite and multiple proportions. Explain what happens when different sample sizes are used during the determination of percent by mass of

Chemistry 6 Quantitative each element in a compound. Calculate the percent by mass of C and O in two different sample sizes of CO to explain the law of definite proportions. Explain why ethane (C2H6) and ethyne (C2H2) illustrate the law of multiple proportions.

Inquiry Extension You are given two compounds. One compound is labeled as a 3.00 g sample of sulfur tetrafluoride (SF4). The other compound is labeled as a 5.00 g sample of an unknown containing sulfur and fluorine. Both samples contain the same relative mass of sulfur and the unknown has the following percent by mass values: F = 78.0% and S = 22.0%. Explain the process and illustrate the steps you would use to determine the identity of the unknown compound using the knowledge you have gained from the laws of definite and multiple proportions. What is the chemical formula of the unknown?

Chemistry 7