4. Pour 5 mL of 1.0 M ammonium hydroxide into each of two test tubes, labeled #3

Question

4. Pour 5 mL of 1.0 M ammonium hydroxide into each of two test tubes, labeled #3 and #4 drops of phenolphthalein to each tube Record the color of the solutions Add 2 : #4-Dark' ink 5. Add 1 scoop of ammonium chloride, NH4Cl, to test tube #3. Shake. Record the color: 6 The equilibrium involved is NH4OH NH4OH Ammonium chloride is a soluble salt that ionizes readily in solution. Explain the color change in terms of Le Châtelier's Principle. Did the solution become more acidic or basic when ammonium chloride was added?

Explanation / Answer

When NH4OH was added to the test tube,

the equilibriumreaction is,

NH4OH <==> NH4+ + OH-

Now when we add NH4Cl, which in solution forms,

NH4Cl ---> NH4+ + Cl-

in solution NH4Cl gives off NH4+ ion. Thus we are adding common ion NH4+ to the already existing NH4+ ions in solution from NH4OH. This would thus increase concentration of NH4+ on the right hand side of the first equilibrium reaction, the state of equilibrium is disrupted. Therefore, more NH4+ would react to form undissociated NH4OH, until all of excess NH4+ is consumed and equilibrium is reestablished. This is accordig to the LeChatellier's principle.

By adding NH4Cl, the solution became less basic as NH4+ reacted with free OH- (base) in solution to form NH4OH.

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