Question

Experiment 22 Advance Study Assignment: Properties of Systems in Chemical Equilibrium Methyl orange, HMO, is a common acid-base indicator. In solution it ionizes according to the equation: HMO(aq) H+(aq) + MO−(aq) red yellow If methyl orange is added to distilled water, the solution turns yellow. If a drop or two of 6 M HCl is added to the yellow solution, it turns red. If to that solution one adds a few drops of 6 M NaOH the color reverts to yellow. a. Why does adding 6 M HCl to the yellow solution of methyl orange tend to cause the color to change to red? (Note that in solution HCl exists as H+ and Cl− ions.) b. Why does adding 6 M NaOH to the red solution tend to make it turn back to yellow? (Note that in solution NaOH exists as Na+ and OH− ions. How does increasing [OH−] shift Reaction 3 in the dis- cussion section? How would the resulting change in [H+] affect the dissociation reaction of HMO?) Magnesium hydroxide is only very slightly soluble in water. The reaction by which it goes into solution is: Mg(OH) (s) Mg2+(aq) + 2 OH−(aq) 2 Formulate the expression for the equilibrium constant, Ksp, for the above reaction. It is possible to dissolve significant amounts of Mg(OH)2 in solutions in which the concentration of either Mg2+ or OH− is very, very small. Explain, using Ksp, why this is the case. Explain why Mg(OH)2 might have very appreciable solubility in 1 M HCl. (Consider the effect of Reaction 3 on the Mg(OH)2 solution reaction.)

Answer 1

HMO(aq) H+(aq) + MO−(aq)

methyl orange is acid base indicator.

methy orange which show red colour in acid solution yellow colour in basic solution

methyl orange indicator added to distill water the solution turn to yellow.Distill water nature is basic nature.

If a drop or two of 6 M HCl is added to the yellow solution, it turns red because HCl is acid . Acid concentration increases.So methyl orange which show red colour in acid solution.HClH+ +Cl^-

Adding 6 M NaOH to the red solution tend to make it turn red to yellow.NaOH is base .in basic solution methyl orange which show yellow colour. By the addition of NaOH basic concentration is increases. NaOHNa+ +OH-

Mg(OH) (s) Mg2+(aq) + 2 OH−(aq)

Ksp =[Mg2+][OH-]

Additon of acid HCl

HClH+ +Cl-

OH-+H+ H2O

If the removal of OH- from the equilibrium by Lechatelier' principle the equilibrium shifts to the right and more Mg+2 goes to solution.