Problem: A common way to make hydrogen gas in the laboratory is to place a metal such as zinc in hydrochloric acid (see the figure). The hydrochloric acid reacts with the metal to produce hydrogen gas, which is then collected over water. Suppose a student carries out this reaction and collects a total of 150.2 mL of gas at a pressure of 746 mmHg and a temperature of 25oC. What mass of hydrogen gas (in mg) does the student collect? (The vapor pressure of water is 23.78 mmHg at 25oC.)

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FREE Expert Solution

Dalton’s Law states that the total pressure inside a container is obtained by adding all the partial pressures of each non-reacting gas


Ptotal=PGas 1+PGas 2+PGas 3...Ptotal=PH2+Pwater746 mm Hg=PH2+23.78 mm Hg

PH2=722.22 mm Hg


Ideal gas equation: moles H2


PVRT=nRTRTn=PVRT


mass = moles x molar mass

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Problem Details

A common way to make hydrogen gas in the laboratory is to place a metal such as zinc in hydrochloric acid (see the figure). The hydrochloric acid reacts with the metal to produce hydrogen gas, which is then collected over water. Suppose a student carries out this reaction and collects a total of 150.2 mL of gas at a pressure of 746 mmHg and a temperature of 25oC. What mass of hydrogen gas (in mg) does the student collect? (The vapor pressure of water is 23.78 mmHg at 25oC.)

Collecting a Gas over Water: The metal zinc is placed in a testtube containing hydrochloric acid. The testtube is connected to a tube that runs into a submerged beaker. The beaker is submerged upside down over water such that teh vapor from the testtub can be collected.


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Our tutors have indicated that to solve this problem you will need to apply the Collecting Gas Over Water concept. If you need more Collecting Gas Over Water practice, you can also practice Collecting Gas Over Water practice problems.

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Based on our data, we think this problem is relevant for Professor Tyson's class at UMASS.