Question

Question #f3be3

Answer 1

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).

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.