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Some students could not attend the lab because of holiday shopping. The professor allowed them to do this lab in the following week. However, by then the stock room had run out of all metals including magnesium. However, there was only one bottle of an unknown metal without any label on it. The professor asked the students to do this experiment with the hint that: one mole of that unknown metal would liberate three moles of hydrogen gas when reacted with HCL. a) What do you think that metal was? The metal was b) Write a balanced equation with its reaction with HCL. c) If 0.05 g of that metal produced 46 ml of Hz at 25°C and 1 atm (the pressure equilibrated and water vapor pressure subtracted), calculate the molar mass of that unknown metal determined from this data. Show your work.

Some students could not attend the lab because of holiday shopping. The professor allowed them to do this lab in the following week. However, by then the stock room had run out of all metals including magnesium. However, there was only one bottle of an unknown metal without any label on it. The professor asked the students to do this experiment with the hint that: one mole of that unknown metal would liberate three moles of hydrogen gas when reacted with HCL. a) What do you think that metal was? The metal was b) Write a balanced equation with its reaction with HCL. c) If 0.05 g of that metal produced 46 ml of Hz at 25°C and 1 atm (the pressure equilibrated and water vapor pressure subtracted), calculate the molar mass of that unknown metal determined from this data. Show your work.

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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This lab is based on Gas Laws, namely, the Ideal Gas law which is: PV = n RT Where P is the pressure of the gas, V is the volume of the gas, n is the number of moles of the substance, R is Gas Constant which is 0.0824 L. atm / mol. K, and T is the Kelvin temperature. If you are using the above value for R, then your pressure must be in atm and volume in liter. The above equation can also be expressed as: PV = (g x RxT) / MM Where g is the mass of the substance in grams used in the experiment and MM is the molar mass of the substance. In this lab the molar mass of the substance you are determining is magnesium. Magnesium is a solid metallic element, and obviously not a gas, so how come its molar mass is determined by the gas law? The answer is simple, it produces hydrogen gas when treated with an acid as follows: Mg (s) + 2 HCI (aq) - Hz (g) + MgCl2 (aq) You can also use sulfuric or nitric acid instead of hydrochloric acid. Experiment: The experiment involves using a piece of magnesium ribbon, weighed accurately and treated with HCl. The magnesium ribbon is immersed in the acid solution in a graduated cylinder or a eudiometer. It is then inverted slowly under a trough of water. The liberated hydrogen gas is collected by the downward displacement of water. The inside pressure of hydrogen gas is then equilibrated with the outside pressure (Boyle's law). The volume of hydrogen gas is accurately measured. The partial pressure of water vapors (Dalton's law of partial pressure) should be taken into account while calculating the pressure of the hydrogen gas collected over water, because the pressure measured is actually the sum of the pressure due to the hydrogen and the partial pressure of water vapors. As shown in the balanced equation above one mole of magnesium would produce one mole of hydrogen gas. Please read the chapter on the gas laws in your lecture text book and watch the video.
Transcribed Image Text:This lab is based on Gas Laws, namely, the Ideal Gas law which is: PV = n RT Where P is the pressure of the gas, V is the volume of the gas, n is the number of moles of the substance, R is Gas Constant which is 0.0824 L. atm / mol. K, and T is the Kelvin temperature. If you are using the above value for R, then your pressure must be in atm and volume in liter. The above equation can also be expressed as: PV = (g x RxT) / MM Where g is the mass of the substance in grams used in the experiment and MM is the molar mass of the substance. In this lab the molar mass of the substance you are determining is magnesium. Magnesium is a solid metallic element, and obviously not a gas, so how come its molar mass is determined by the gas law? The answer is simple, it produces hydrogen gas when treated with an acid as follows: Mg (s) + 2 HCI (aq) - Hz (g) + MgCl2 (aq) You can also use sulfuric or nitric acid instead of hydrochloric acid. Experiment: The experiment involves using a piece of magnesium ribbon, weighed accurately and treated with HCl. The magnesium ribbon is immersed in the acid solution in a graduated cylinder or a eudiometer. It is then inverted slowly under a trough of water. The liberated hydrogen gas is collected by the downward displacement of water. The inside pressure of hydrogen gas is then equilibrated with the outside pressure (Boyle's law). The volume of hydrogen gas is accurately measured. The partial pressure of water vapors (Dalton's law of partial pressure) should be taken into account while calculating the pressure of the hydrogen gas collected over water, because the pressure measured is actually the sum of the pressure due to the hydrogen and the partial pressure of water vapors. As shown in the balanced equation above one mole of magnesium would produce one mole of hydrogen gas. Please read the chapter on the gas laws in your lecture text book and watch the video.
2. Some students could not attend the lab because of holiday shopping. The professor allowed them to do this lab in the following week. However, by then the stock room had run out of all metals including magnesium. However, there was only one bottle of an unknown metal without any label on it. The professor asked the students to do this experiment with the hint that: one mole of that unknown metal would liberate three moles of hydrogen gas when reacted with HCI. a) What do you think that metal was? The metal was b) Write a balanced equation with its reaction with HCl. c) If 0.05 g of that metal produced 46 ml of Hz at 25°C and 1 atm (the pressure equilibrated and water vapor pressure subtracted), calculate the molar mass of that unknown metal determined from this data. Show your work.
Transcribed Image Text:2. Some students could not attend the lab because of holiday shopping. The professor allowed them to do this lab in the following week. However, by then the stock room had run out of all metals including magnesium. However, there was only one bottle of an unknown metal without any label on it. The professor asked the students to do this experiment with the hint that: one mole of that unknown metal would liberate three moles of hydrogen gas when reacted with HCI. a) What do you think that metal was? The metal was b) Write a balanced equation with its reaction with HCl. c) If 0.05 g of that metal produced 46 ml of Hz at 25°C and 1 atm (the pressure equilibrated and water vapor pressure subtracted), calculate the molar mass of that unknown metal determined from this data. Show your work.
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