Chemistry Practice Problems Collecting Gas Over Water Practice Problems Solution: A common way to make hydrogen gas in the laborator...

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Solution: A common way to make hydrogen gas in the laboratory is to place a metal such as zinc in hydrochloric acid. 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 169.7 mL of gas at a pressure of 749 mmHg and a temperature of 25°C. What mass of hydrogen gas (in mg) does the student collect? Express your answer using three significant figures.

Problem

A common way to make hydrogen gas in the laboratory is to place a metal such as zinc in hydrochloric acid. 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 169.7 mL of gas at a pressure of 749 mmHg and a temperature of 25°C. What mass of hydrogen gas (in mg) does the student collect? Express your answer using three significant figures.




Solution

For problems that involve collecting gas over water, we should note that the total pressure is the sum of the partial pressure of the gas and water. We have to look for the value for the partial pressure of water at a certain temperature from literature (books/tables). 


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