How could this experiment be used to find the molecular mass of an unknown gas?

Question

1.Obtain a length of glass tubing. Make sure it is completely dry. Lay the tubing on your bench.

2. Place one stopper with a cotton swab in each end of the tubing. Using a crayon, mark the glass to indicate the position of the end of each swab

3. Remove the cotton swabs from the tubing. Mark the stem of one of the swabs with the marker for purposes of identification. Using dropper pipets in the hood, place about five drops of concentrated NH3 solution on the marked cotton swab. Place about five drops of concentrated HCl on the other swab.

4. Immediately and simultaneously insert the moistened ends of the cotton swabs into opposite ends of the tube, to the lines previously marked. Place the tube on a dark surface.

5. After several minutes, a white ring will form where the gases HC1 and NH3 meet inside the tube to form the white powder NH4Cl (ammonium chloride). Using a crayon, mark the point on the tube where the white ring is first formed.

6. Measure the distance traveled by each gas. Record in the data table.

Answer 1

Graham's law of diffusion states that the ratio of the rates of diffusion of two gases is related to the square root of the molecular masses.

The distance the ammonia and hydrogen chloride gases travel is directly related to their rates of diffusion. If we know the molecular mass of one of the gases, we can calculate the molecular mass of the other gas.

Distance travelled by A / distance travelled by B = sq.root (M_a / M_B). Knowing gas A or B, you can calculate the molecular mass of the other gas.

Answer 2

Do you mean the molar mass?