The indicator constant of phenolphthalein is approximately 10^(-8).A solution is prepared by adding 100.01 c.c. of 0..01 N sodium hydroxide to 100.00 c.c. of 0.01 N hydrochloric acid.If a few drops of phenolphthalein are now added.what traction of the indicator is converted to its coloured form ?

The indicator constant of phenolphthalein is approximately 10^(-8).A s

1.	The indicator constant of phenolphthalein is approximately 10^(-8).A solution is prepared by adding 100.01 c.c. of 0..01 N sodium hydroxide to 100.00 c.c. of 0.01 N hydrochloric acid.If a few drops of phenolphthalein are now added.what traction of the indicator is converted to its coloured form ?
Answer» `1/3` `3/4` `1/2` `9/11` SOLUTION :millimole, `UNDERSET(100.01xx0.01)(NaOH)underset(" "100xx0.01)(+HCl)toNaCl+H_2O` So, NaOH left =0.0001 Hence, CONCENTRATION of `OH^(-) =0.0001/200.01=0.0001/200` `HPhhArr H^+ + Ph^(-)` `K_a=([H^+][Ph^(-)])/([HPH])` `implies 10^(-8)=(k_w[Ph])/([OH^(-)][HPh])=((10xx^(-14)xx[Ph])/0.0001)/(200)[HPh], " " ([Ph^(-)])/([HPh])=1/2` so `([Ph^(-)])/([Ph^(-)]+[HPh])=1/3`