Volume of gas collected (mL)
Barometric pressure (atm)
Room Temperature (°C)
Vapor pressure of the water (torr)
1. Write the balanced equation for the reaction conducted in this lab, including appropriate phase symbols. (2 points)
Mg(s) + 2HCl(a) + H2O(a) -> MgCl2(s) + H2 (g)
2. Determine the partial pressure of the hydrogen gas collected in the gas collection tube. (3 points)
1.1 atm = 0.026 atm + h2
3. Calculate the moles of hydrogen gas collected. (4 points) !
n = 1.074 atm x 0.03 L / 0.0821 x 295.15 K = 0.00133 mol H2
4. If magnesium was the limiting reactant in this lab, calculate the theoretical yield of the gaseous product. Show all steps of your calculation. (4 points)
.032 g Mg * 1 mol Mg / 24.305 g Mg * 1mol h2 / 1 mol Mg = 0.0131 mol
5. Determine the percent yield of this reaction, showing all steps of your calculation. (3 points)
Percent Yield = 0.00133 /0.0131 mol H2 × 100 = 10. 15 %
1. Would the following errors increase, decrease, or have no effect on the calculated moles of gas collected in the experiment? Explain your answers in complete sentences.
a) The measured mass of the magnesium was smaller than the true mass. (3 points)
It would not affect the number of moles calculated because it was not used to measure the moles of the gas.
b) The actual temperature of the hydrogen gas is less than room temperature. (3 points)
If the gas was cooler than its surroundings, its density would be greater, and the volume would appear to be smaller. Charles’ Law says that a gas’ volume is directly proportional to its temperature, if the pressure on it is constant.
2. Explain in terms of particle collisions and Dalton’s law why it can be assumed that the total pressure inside the gas collection tube is equal to the atmospheric pressure outside of the tube. (4 points)
The particles inside the container are exerting force on the walls of the container, while the particles outside of the container are also exerting force. If there were any less pressure from the inside, the tube would collapse. If there were any less pressure from the outside, the tube would explode.
3. If an undetected air bubble was trapped inside the gas collection tube, how would this affect your calculated percent yield? Explain your answer. (4 points) The bubble would take up space in the container and the volume would decrease. Therefore the percentage yield would be incorrect.