Experiment 13 – The Burning of a CandleExperiment 14 – The Gasimetric Analysis of

a Nitrite Complex

Randy W. HubaPartner: Chris Held

TA: Veronica De SilvaSection N2

Date Done: 9/22/99Date Due: 9/29/99

Experiment 13:

Purpose: To analyze the burning of a candle several ways. Also to understand combustion reactions. Also collect evidence to support or refute Lavoisier’s theory of combustion.

Procedure: See lab manual page 154.

Results: tissue Tissue had black deposit from bottom of beakerwatch glass condensation formed on watch glass mass change .02g time of one & flask 11.5 secondstime of two & flask 5.44 secondsone & bromothymol blue nothing happenedwater height 4.0 cmshaking with bromothymol blue the water turned yellowone & limewater the water remained almost clearshaking with limewater The lime water turner from clear to milky.volume before one 262mLvolume after one 227mLpressure 739.5temperature 22

Discussion:

This experiment supported Lavoisier’s theory of combustion. It showed in many different fashions how water, carbon dioxide, and elemental carbon are produced in combustion. Carbon deposits were left on the bottom of the flask after it was burned. This is elemental carbon. Also, water and carbon dioxide are produced as products of combustion. Water being produced is evident from the condensation on the watch glass while the bromothymol blue changing colors to yellow show how carbon dioxide is produced. Also, the limewater turning milky shows carbon dioxide is evident. Because the water level in the flask rose, this shows how the oxygen was burned creating a vacuum. The possible errors are listed in question number four.

Questions: 1. The fact that the water rises is attributed to its replacing the 20% of air which

is oxygen. Would this explanation agree with your results? Why or why not?This statement is halfway correct. When the oxygen is burned it creates a vacuum in the flask. The seal between the glass and the tub is not tight so the vacuum sucks water into it. Therefore the water does rise because it replaces the oxygen. Also the air pressure on the inside of the flask is less than on the outside, therefore the water level rises.

2. Is the water produced in the burning of a candle in its gaseous or liquid phase? What evidence do you have for your answer?

The water was in the gas phase. This is evident by the condensation that formed on the watch glass.

3.a. Suppose the carbon dioxide dissolves in the water as soon as it is

produced. Further suppose that only the liquid water is produced as the candle burns. How high should the column of water rise under these circumstances?

If the water is not in gas form the water should raise a little higher than without it. This is evident by the equation on page 153. 1.4

b. Suppose that the carbon dioxide does not dissolve, but remains in the gas phase. How high should the water column rise, if the water produced is actually in the liquid phase?

If the carbon dioxide remains undissolved, the water level would not raise as high. .3

c. Suppose that both the carbon dioxide and water are in the gas phase. How high should the water rise?

The carbon dioxide and water were mostly in the gaseous phase, therefore the water would rise only a small amount less than predicted by the equation on page 153.

4. List five sources of error in this experiment that would affect you knowledge of the quantitative relationship between the amounts of wax and oxygen consumed in the combustion of the candle and the amounts of carbon dioxide and water produced.

1. If any measurements were taken wrong then the relationship would be off.

2. If different candles were used for one type of experiment the relationship would be off.

3. If different kinds of wax were in the candles the relationship would be off.

4. If there was any water in the flask before the candle was burned, the candle height would be off.

5. If the flask was inverted over the candle to slowly, the difference in mass would be wrong.

Experiment 14:Purpose: To determine the percent of nitrogen in a sample and compare the

experimental value to the value calculated from the formula of thecompound.

Procedure: See lab manual pages 162-164.

Data: See attached sheet

Results:Trial One Two Three

Mass of sample .1082 .1084 .1085Volume of gas collected 29.95ml 29.15 31.15

Change in H 29.95mm 29.15 31.15Barometric P 739.5torr 739.5 739.8

Room Temperature 22 22 22Vapor P 19.81 19.8 19.8

Moles of N2 .001169 .001137 .001222Mass of N2 .01645 .016 .0172Percent N2 15.2 14.7 15.9

Average Percent 15.3

Theoretical Percent 16.7Percent Error 8.38

Sample Calculations:

P = 740 torr - VP - h/13.6,P is the pressure of Nitrogen collected in units of torrVP is the vapor pressure at 22 Celsius, from Appendix B h is the difference in height between the level in water in the beakerand the level of water in eudiometer tube Find number of moles of nitrogen collected: n = PV/RT where: V is in L grams (W)of Nitrogen in your complex: W= n*14.07gthe % of nitrogen in your sample: %N = (W/M) * 100%where M= mass of nitrite sample used in this run (from your data sheet, is themass of sample in vial)

Theoretical Value:T = (6*14.07)/molecular weight * 100%, where

Discussion:

The theoretical value was relatively close to the experimental value. And the percent error was relatively small. There were many possible places for error to occur. For example if the previous experiment was performed in error, the compound may not have the nitrogen percentage it was supposed to. There could also be errors in performing the experiment. If the experimenter let acid leak into the vial before the stopper was in place, then some of the nitrogen could escape. In general this lab was successful.