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Graham's Law of Diffusion Lab
Theory
Graham's Law of Diffusion deals with the rate diffusion/effusion of gases (ri). It states that the ratio of the rate of diffusion of two gases is inversely proportional to the ratio of the square root of the gases molar mass (molecular weight). The law assumes a given number of particles of each gas (1 mole of each gases).
The rate of diffusion is defined as the distance the gas particle travels in a given time. So if you release the gases at the same time, the one with the higher rate of diffusion will have traveled further or ri = di where d is the disstance in cm (or other length units)
In this lab, we will look at the gases, ammonia (NH3, and hydrogen chloride (HCl). The HCl looks like hydrochloric acid. It is but since acids only exist in the aqueous phase, then we call this compound another name in the gas (hydrogen chloride). Hydrochloric acid is actually generated from bubbling this compound through water. So, to generate hydrogen chloride, we will simply expose concentrated hydrochloric acid to the air. The concentrated acid is located in the exhaust hood. DO NOT TAKE THE CONTAINER OUT OF THE HOOD.
The ammonia, NH3 will be generated from the aqueous solution ammonium hydroxide, NH4OH, that decomposes into ammonia and water in the following equation, 1 NH4 --> 1 H2O + 1 NH3. The concentrated ammonium hydroxide solution will be located in the window sill (back wall window nearest the fan).
These two gases will react together to form a white solid, ammonium chloride (NH4Cl). We will use this fact to determine how far, in cm, each gas has traveled over a given time. From this data, we can then determine the relative ratio of rate of diffusion of the gases. We can compare this experimental ratio to the ratio determine from the inverse square root of the molar masses of the two gases. If Graham's Law is correct, these two ratio should approximately the same values.
Directions
Q-tips are located next to each chemical
1. Take a glass tube and a meter stick and put it at your lab station. Label each end of tube via small pieces of paper using wax pencils.
2. One learner will dip a Q-tip into the concentrated ammonium hydroxide solution and place it next to one end of glass tube.
3. The other learner will do the same with the hydrochloric acid.
4. At the same time, put the Q-tip into each end of the glass tube. One half of the Q-tip should be in the glass tube (each Q-tip should be approximately the same distance into the tube).
VERY IMPORTANT< DO NOT GET THE TWO Q-TIPS CLOSE TO EACH OTHER
Directions:
1. Each lab partner obtain a balloon.
2. One partner needs to add 1 drop of Gas 1 to the inside of the balloon.
3. Another partner add one drop of Gas 2 to the inside of balloon.
4. The partner can come together and blow up each balloon to the same diameter.
5. Then put your balloon to your nose and sniff.
6. Tell when you can smell the gas through the balloon.
7. Indicate/write down which gas you can smell first.
Observation / Data