89 LAB 7: DETERMINATION OF THE MOLAR VOLUME OF A GAS AND THE GAS CONSTANT R POST
ID: 1045820 • Letter: 8
Question
89 LAB 7: DETERMINATION OF THE MOLAR VOLUME OF A GAS AND THE GAS CONSTANT R POST-LAB QUESTIONS 1. For each of the following experimental erors or mistakes in doing this experiment, what will be the effect upon the experimental value of R that will be computed? Will the reported value of R a) increase b) decrease or c) not change? IN EACH CASE JUSTIFY YOUR ANSWER WITH SEVERAL SENTENCES. a. While the solid Mg was reacting, a small piece broke off, climbed to the top of the eudiometer tube and adhered to the walls of the tube while the reacting HCI dropped to a lower level in the eudiometer tube. b. A student failed to correct the pressure by subtracting the vapor pressure of the water in the eudiometer tube. 2. For each of the following experimental errors or mistakes in doing this experiment, what will be the effect upon the experimental value of the molar volume of a gas at STP? Will the reported value a) increase b) decrease or c) not change? IN EACH CASE JUSTIFY YOUR ANSWER WITH SEVERAL SENTENCES. a. When the student determined the volume of the hydrogen in the eudiometer tube, the level of the meniscus in the tube was considerably higher than the meniscus in the graduated cylinder. b. When the student weighed her piece of magnesium ribbon before it was weighed she observed that the ribbon had a thick coat of tarnish. The student ignored the tarnish and weighed the metal sample as directed.Explanation / Answer
1. The equation that we use in the experiment is ideal gas law PV=nRT; R = PV/nT. R = Gas constant, P = pressure, V = Volume, n = no. moles, T = Temperature
a.Decrease the R value.
While Mg was reacting a small piece left unreacted, which means no. of moles of Mg what calculated and actually reacted is different. Only lesser amount of Mg reacted but we use larger value in the equation. Which reduces the experimentally determined R value. The other way is, the P and V of the reaction will be less than what expected since less Mg reacted, so lower the R value.
b. Increase the R value.
Student failed to subtract the vapor pressure of water, means the actual measured pressure is more than the pressure generated by H2 gas, so the measured R will be increased.
2.
a. The experimental volume of gas evolved will increase (more than expected), since the volume student measured is more than blank measurement, so the measured volume is more than the actual volume.
b. The experiment volume of gas evolved will decrease (less than expected), since the actual weight of magnesium metal weighed is less than required. i.e. weight the student measures is of Mg metal and magnesium oxide, the metal content in MgO is less than pure metal.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.