Question #f3be3

1 Answer
Aug 21, 2017

Answer:

Here's my explanation.

Explanation:

Bromothymol blue (HBtb) is a weak acid in which the molecular form and the ionized form have different colours.

#color(orange)("HBtb") + "H"_2"O" ⇌ color(blue)("Btb"^"-") + "H"_3"O"^"+"#

The unionized form is yellow (below pH 6.0), while the ionized form is blue
(above pH 7.5).

HBtb

When you place #"HBtb"# in a solution of sodium hydroxide, the #"OH"^"-"# ions react with the #"H"_3"O"^"+"# ions and convert them to water.

Le Châtelier's Principle states that, when a stress is applied to a system at equilibrium, the system will respond in such a way as to reduce the stress.

When you add #"NaOH"# to #"HBtb"#, you are removing a product (#"H"_3"O"^"+"#) from the equilibrium reaction.

The system responds by producing more #"H"_3"O"^"+"#.

At the same time, it produces more #"Btb"^"-"#, so the solution turns blue.