Formulation, Testing of Hypothesis, and Experimental Design

Topics: Diffusion, Molecular diffusion, Chemistry Pages: 5 (1264 words) Published: August 6, 2013
Name: Joie Vincent R. DagohoyDate performed: 07-01-13
Student Number: 2009-33281Date submitted: 07-08-13

Exercise 2
Formulation, Testing of Hypothesis, and Experimental Design

I. Objectives:

a. to define diffusion and demonstrate this process in gases
b. to cite molecular weight and time as two factors affecting the rate of diffusion
c. to formulate a hypothesis on the relationship of each of these factors on the rate of diffusion
d. to conduct and experiment to determine the effects of the two factors on the rate of diffusion
e. to compute the partial rate and average rate of diffusion
f. to conclude on the relationships of molecular weight and time on the rate of diffusion

II. Materials:

A. Formulation of Hypothesis
a. Apparatus
- glass tube
- cotton balls
b. Substances
- hydrochloric acid (HCl)
- ammonium hydroxide (NH4OH)
B. Testing the Hypothesis Concerning the Rate of Diffusion
a. Apparatus
- petri dish of agar-water gel with three wells
b. Substances
- potassium permanganate (KMnO4)
- potassium dichromate (K2CR2O7)
- methylene blue

III. Procedure:

A. Formulation of Hypothesis
1. Fasten the glass tube to a ring stand.
2. Simultaneously moisten two cotton balls with hydrochloric acid and ammonium hydroxide.
3. Plug each end of the glass tube with the cotton balls simultaneously.
4. Watch the formation of white smoke inside the tube and mark its position. Measure the distance (in cm) of the cottons to the smoke and tabulate. B. Testing the Hypothesis Concerning the Rate of Diffusion

1. Obtain a petri dish of agar-water gel with three wells, and label each well as potassium permanganate (KMnO4), potassium dichromate (K2CR2O7), and methylene blue.
2. Place a drop of each substance into the well and cover the petri dish.
3. Measure the diameter (in mm) of the colored area. Set as data for zero minute.
4. At three-minute intervals for thirty minutes, measure the diameter of the colored area of each substance.
5. Tabulate data and draw the set-ups at zero and after thirty minutes.

IV. Results:

Table 2.1: Distance of white smoke from the cotton balls
Cotton with| Distance (cm)|
Hydrochloric acid (HCl)| 10|
Ammomium Hydroxide (NH4OH)| 30|

Table 2.2: Diameter (mm) of the colored area and difference in diameter through time Time| KMnO4| K2CR2O7| Methylene Blue|
0| 8| 8| 8 (0)|
3| 12 (4)| 9 (1)| 8 (0)|
6| 14 (2)| 9 (0)| 8 (0)|
9| 15 (1)| 9 (0)| 8 (0)|
12| 15 (0)| 10 (1)| 8 (0)|
15| 16 (1)| 12 (2)| 8 (0)|
18| 17 (1)| 12 (0)| 8 (0)|
21| 18 (0)| 12 (0)| 8 (0)|
24| 18 (0)| 12 (0)| 8 (0)|
27| 19 (1)| 13 (1)| 8 (0)|
30| 20 (1)| 13 (1)| 8 (0)|

Figure 2.1: Illustration showing the difference in size of colored area through time
a. for KMnO4
At zero minute| After 30 minutes|
| |
b. for K2Cr2O7
At zero minute| After 30 minutes|
| |
c. for methylene blue
At zero minute| After 30 minutes|
| |

V. Discussions:

The white smoke that appeared in the glass tube is NH4Cl. It was the result when the aqueous solutions of NH4OH and HCl are placed in cottons at both ends of the glass tube. NH4OH then formed a gas called NH3 or better known as ammonia. It was then mixed with the HCl gas released from its aqueous solution. Since both gases are trapped, they mixed and formed NH4Cl.

As shown on Table 2.1, the substance that diffused faster is the one that is in the cotton with NH4OH, or the gas that is called ammonia (NH3) since it reached the HCl side faster and it travelled a greater distance compared to HCl gas. The very applicable factor that affected this experiment’s rate of diffusion is the molecular weight of the compound. Since NH3 gas has a lighter molecular weight (17 g/mol) than HCl gas (which has 36.45 g/mol), it diffused faster. Just as the analogy that big objects move slower than...

References: 1. Article about Plant Physiology. Retrieved July 6, 2013 from
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