Rate of Diffusion of two gases – Ammonia (NH3) and Hydrochloric Acid (HCl)

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)

Introduction: 

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.

Materials/ Apparatus:

Glass tubing, rubber bung, concentrated ammonia solution, concentrated hydrochloric acid, cotton and tape, stop-watch

Method / Procedure:

  1. Set up apparatus as shown below.
  2. Soak one cotton wool in the concentrated ammonia solution and a next piece in the concentrated hydrochloric acid.
  3. 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.
  4. Begin timing and record the time taken for the white ring to for in the glass tube.
  5. 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
Diagram of apparatus showing the diffusion of ammonia and hydrochloric acid

Diagram of apparatus showing the diffusion of ammonia and hydrochloric acid

 

Suggested Results:

Diagram showing the reaction of  the diffusion of ammonia and hydrochloric acid

Diagram showing the reaction of the diffusion of ammonia and hydrochloric acid

  1. After the cotton wools were placed in the tube, it took approximately 13mins and 22 seconds for a reaction to start taking place.
  2. 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
  3. 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)

Discussion/ Answers:

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:

  1.  Inaccuracy in timing due to strips not changing entirely and the time is recorded too soon.
  2. Inconsistency with volume of ammonia used.

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