Question

Please help with the prelab questions. Need explanations too.

Using the balanced chemical equation, you will calculate the quantity of hydrogen gas generated by the reaction of a known mass of magnesium metal with excess HCl. The hydrogen gas you generate will be collected in a graduated tube called a eudiometer. You will need to correct for the fact that conditions in the lab are not at STP, and you will need to use Dalton’s Law of Partial Pressures to correct for the presence of other gases, namely water vapor, in your sample.

Table 1. Temperature Dependence of Water Vapor Pressure
T (°C)	P (torr)		T (°C)	P (torr)		T (°C)	P (torr)
18	15.48		22	19.83		26	25.21
19	16.48		23	21.07		27	26.74
20	17.54		24	22.38		28	28.35
21	18.65		25	23.76		29	30.04

DETERMINING THE MOLAR MASS OF A GAS

In the second experiment, you will determine the molar mass of an unknown volatile liquid using Equation 4. A small quantity of the liquid will be placed in a pre-weighed flask and vaporized by heating with a boiling water bath. Once the liquid has fully vaporized and the air has been expelled from the flask, the flask will be allowed to cool. The mass of the condensed liquid and the volume of the flask will be measured. By assuming the temperature of the vapor is equal to the temperature of boiling water and that the pressure is equal to atmospheric pressure, the molar mass of the unknown liquid will be calculated.

6! Prelab (due at the beginning of lab)

A sample of gas at 21.0ºC is collected above water. The atmospheric pressure that day is 758 Torr. What is the partial pressure of the dry gas in Torr and in atm?

Use the ideal gas law to determine how many moles of helium are in a 2.50-L balloon at 1.00 atm and 25.0 °C?

Use the ideal gas law to calculate the molar volume of an ideal gas at STP. Hint: the term “molar” implies that one mole of gas is present.

A student determines that a gas has a density of 1.948g/L at a pressure of 748.2 mmHg and a temperature of 22.9ºC. What is the molar mass of the gas? Hint: assume that you have 1.000L of gas.