Question

Activity 4: Equilibrium of solid ammonium chloride with ammonium chloride in aqueous solution. NH4Cl(s) +H2O(l)  NH4+(aq) + Cl-(aq) (ammonium chloride) (ammonium ion) Procedure * Pour about 75 mL of tap water into a 150-mL beaker and heat to boiling on a hot plate. * While waiting for the water to boil, place approx. 1 mL of a saturated NH4Cl solution into a small, clean, dry test tube. *To this test tube, add concentrated HCl solution one drop at a time, while stirring with a glass stirring rod, until you observe a change. Note: HCl solution contains H+ and Cl- ions. *Use a test tube holder and place the test tube into the boiling water bath. Leave it in the bath for a few minutes, stirring the contents, until you observe a change. *Use a micro spatula to place a few crystals of solid ammonium chloride on the bottom of another small, clean, dry, test tube. Touch the bottom of the tube to qualitatively note warmth or coolness. (Do not let the warmth of your hand change the tube temperature.) Now add about 10 drops of DI water quickly to this tube and feel the tube again, to see if there is any temperature change. Observations and Interpretations to be Handed In Activity 4: Observations and Interpretations NH4Cl(s) + H2O(l)  NH4+(aq) + Cl-(aq)

1) What did you observe when you added the concentrated HCl solution to the saturated solution of ammonium chloride?

2) Interpret the observation in 1, in terms of the equation given above and LeChatelier’s Principle.

3) What did you observe when you placed this test tube in the boiling water bath?

4) Based on your observations in 3, which of the reactions in the equilibrium, written above, is endothermic, and which is exothermic? Explain.

5) What temperature change did you observe when ammonium chloride was dissolved in water?

6) What does such a temperature change indicate, and is this consistent with what you observed in 3? Explain.

Answer 1