Rate of Diffusion of two gases – Ammonia (NH3) and Hydrochloric Acid (HCl)
Aim / Objective:
To compare the rates of diffusion of two gases- Ammonia (NH3) and Hydrochloric Acid (HCl)
The particles in a fluid are in continuous random motion. In light of this, gases and gaseous mixtures spread out to occupy any space available to them, eventually acquiring a uniformed composition. The process by which fluid mixtures kept a constant temperature becomes uniformed is known as diffusion.
In this experiment, a comparison on the rate of diffusion of ammonia and hydrogen chloride will be done.
Glass tubing, rubber bung, concentrated ammonia solution, concentrated hydrochloric acid, cotton and tape, stop-watch
Method / Procedure:
- Set up apparatus as shown below.
- Soak one cotton wool in the concentrated ammonia solution and a next piece in the concentrated hydrochloric acid.
- Insert both cotton wools simultaneously at points A (one end of the tube) and B (the other end of the tube) respectively and then quickly insert rubber bungs at both ends of the as shown in the diagram.
- Begin timing and record the time taken for the white ring to for in the glass tube.
- Record the following distances:
- From End A to the center of the white ring and label this distance as X
- From End B to the center of the white ring, and label this distance as X2
- After the cotton wools were placed in the tube, it took approximately 13mins and 22 seconds for a reaction to start taking place.
- When the two gases reacted there was a white ring formed 2.5cm from the cotton wool with the HCl and 29.5cm from the cotton wool with the NH3
- The length of the tube was estimated to be 32cm and from the experiment, one can deduce that HCl is more dense than NH3 because the NH3 traveled a farther distance than the HCl in the same period of time , hence the white ring formed closer to the cotton with the HCl (Hydrogen Chloride)
1. Define diffusion.
>>>> Diffusion is the process by which molecules or ions move from an area of high concentration to a region of low concentration along a concentration gradient.
2. Use the values of X1 and X2 and time (t1) to calculate the relative rates of movements of ammonia gas and hydrogen chloride under similar conditions.
>>> Rate = distance / time
Time = 13m 22s gives 802 seconds
(a) Distance travelled by HCl = 0.25m
Rate of HCl = Distance/ Time = 0.25m/ 802 seconds
= 3.12 x10-4 ms-1
(b) Distance travelled by NH3 = 0.295m
Rate of NH3 = Distance/ Time = 0.295m/ 802 seconds
= 3.67 x10-4 ms-1
3. Calculate the relative molecular masses of ammonia Mr(NH3) and Mr(HCl)
>>> Relative molecular mass of HCl =
H Cl = HCl
1 35.5 = 36.5
>>>Relative molecular mass of NH3 =
N H3 = NH3
14 (3×1) = 17
Explain why the rates of diffusion for the two gases are different.
>>> The rate of diffusion for the gases were different even though they were under the same conditions was a result of ammonia being less dense and moving at a further distance than the hydrogen chloride. The formula given for rate is distance/ time thus ammonia’s rate of diffusion higher than that of HCl as it moved a further distance.
In one short sentence explain why concentration affects rate of diffusion.
>>> The steeper the concentration gradient is the faster the rate of diffusion.
Write a balanced equation for the formation of the white ring.
>>> NH3(g) + HCl(g) = NH4Cl
Ammonia + hydrogen chloride = ammonium chloride.
Sources of Error/ Limitations/ Assumptions:
- Inaccuracy in timing due to strips not changing entirely and the time is recorded too soon.
- Inconsistency with volume of ammonia used.
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