Question

The flask with phenolphthalein and NaOH changes color when the ___ gas formed during respiration was passed through the solution. The gas dissolves in the solution and forms____. Select an answer and submit. For keyboard navigation, use the up/down arrow keys to select an answer. a) oxygen..........water b) carbon dioxide.......water c) carbon dioxide........carbonic acid d) nitrogen........ammonia

Answer 1

Answer:

c

Explanation:

The flask with phenolphthalein and NaOH changes color when the carbon dioxide gas formed during respiration was passed through the solution. The gas dissolves in the solution and forms carbonic.

The dissolution of CO2 into an aqueous solution of NaOH is a two steps reaction.

1. CO2 first reacts with water to form carbonic acid

                $CO_2(aq)+H_2O(l) --> H_2CO_3(aq)$

This makes the phenolphthalein to change color.

2. The product in step 1 reacts with NaOH to form NaHCO3 and water

             $H_2CO_3(aq)+NaOH(aq)-->NaHCO_3(aq)+H_2O(l)$

Hence, the correct option is c.