# Collecting Gas Over Water Practice Problems - Chemistry Gas Laws | Summary and Q&A

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September 19, 2017
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The Organic Chemistry Tutor
Collecting Gas Over Water Practice Problems - Chemistry Gas Laws

## TL;DR

Analyzing gas collection over water problems and calculating the mass of collected gases in various scenarios.

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### Q: How does gas collection over water affect the total pressure of the system?

Gas collection over water involves considering the partial pressure of the gas and the vapor pressure of water. The total pressure is the sum of these partial pressures.

### Q: Why is it important to convert the partial pressure of a gas to atm when using the ideal gas law equation?

The ideal gas law equation uses atm as the unit for pressure. To ensure consistency in units, the partial pressure of the gas needs to be converted to atm before using the equation.

### Q: How is the moles of a gas calculated using the ideal gas law equation?

The ideal gas law equation, PV = nRT, can be rearranged to solve for n. By substituting the known values for P, V, R, and T, the moles of the gas can be calculated.

### Q: How is the mass of a gas calculated from the moles of the gas?

The molar mass of the gas is multiplied by the calculated moles to obtain the mass of the gas. This is done by using the molar ratio between the gas and the reactant or product in the balanced chemical equation.

## Summary & Key Takeaways

• Gas collection over water involves considering the partial pressure of the gas and the vapor pressure of water.

• By using the ideal gas law equation, the moles of gas can be calculated, which can then be used to determine the mass of the gas.

• The molar mass of the gas is multiplied by the calculated moles to obtain the mass.