Question

A piece of lithium metal is added to a beaker that contains water and phenolphthalein. Using what you know about the properties of bases, choose the best explanation for what you observe.

1) The phenolphthalein is turning pink because an acid is forming

2) The phenolphthalein is turning pink because a base is forming.

3) The phenolphthalein is turning pink because the reaction is at equilibrium.

Answer 1

The answer is “The phenolphthalein is turning pink because a base is forming.”

Answer 2

2) The phenolphthalein is turning pink because a base is forming.

Step-by-step explanation:

Lithium metal reacts with water to form lithium hydroxide and hydrogen gas.

Li + H₂O → LiOH + H₂

LiOH is base. LiOH dissociates in water to release the hydroxyl ion OH⁻ which makes the pH greater than 7.0.

Phenolphthalein is an acid base indicator. It is colorless in acidic solution and turns pink in basic solution.