# 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.

## Key Insights

• 🫢 Gas collection over water involves considering the total pressure, which is the sum of the partial pressures of the gas and water vapor.
• 🫢 The partial pressure of the gas can be calculated by subtracting the vapor pressure of water from the total pressure.
• 🫢 Using the ideal gas law equation (PV = nRT), the moles of the gas can be calculated by rearranging the equation.
• 🫢 The mass of the gas can be determined by multiplying the calculated moles by the molar mass of the gas.
• 🥳 The molar ratio between the reactants or products in the balanced chemical equation is used to convert the moles of one substance to the moles of another.
• 💆 The mass percent of a compound in a sample can be calculated by dividing the mass of the compound by the total mass of the sample and multiplying by 100%.
• 💦 The vapor pressure of water at a given temperature is an important factor in gas collection over water problems.

## Transcript

in this lesson we're going to go over a few gas collection over water problems like this one 37 liters of nitrogen gas was collected over water at 25 degrees celsius at 790 torr the vape pressure of water is 23.8 torr at 25 celsius how many grams of m2 was collected so what you need to understand is whenever you have a gas that's being collected ov... Read More

## Questions & Answers

### 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.