Question

1. What do you feel is the largest source of experimental error in your determination of R?

2. What would be the effect (increase, decrease, or no change) on the calculated value of R of each of the following experimental errors? a. The liquid level in the eudiometer tube is lower than that in the beaker, but this is not taken into consideration in the calculations.

b. The balance used to weigh the magnesium gives a mass that is higher than actual.

c. Some H2 escapes into the beaker during the reaction.

3. Most top-loading balances used in this experiment measure a mass only to the nearest mg ±0.001g. This significantly affects the calculation of R in this experiment. Explain why this is so. How might the procedure be modified to compensate for this systematic error?

Answer 1

Since the procedure of the experiment is not shown, I'll assume you mixed to chemicals to produce gas, and then you measured the volume of water displaced by the gas, and the weight of the gas was measured by initial and final difference in the test tube

1. The biggest source of error when you work with gases, usually is avoiding the gas to escape. When you have a gas leak, the ammount of gas loose is big even if the leak is really small, also if you do not get equal pressure in your test tube and in the edimeter, you will have an error in your calculations.

2

a If the water level is lower, the pressure is going to be higher than the external pressure, R is going to be lower

b your "n" is going to be higher, thus R lower

c R is lower since the volume measured is lower

3. An error in the measurment of the mass is going to affect the calculation in the moles of gas produce, to reduce this error you could make more measurments in order to get a more accurate value and its uncertainity. Also you you could make a calibration of the balance using known volumes of water at certain temperature, and get what is the error in each measurement.