Question

Results:

As we added 14 drops of 0.1M NaOH to 15 drops of 0.1M HCl and 1 drop of BTB, we have the solution turned to blue.

Question:

What makes us verify that the reaction is happening? and What is the reaction stoichiometry according to the experimental data? Is this reasonable?

Answer 1

Bromothymol blue (BTB) is an indicator used in acid base titration. In acidic medium, the color is yellow and in basic medium, the color is blue.

When 1 drop of BTB is added to 15 drops of 0.1 M HCl, the color will be yellow. When 14 drops of 0.1 M NaOH are added to this, the color changes to blue. This suggests that HCl is completely neutralsied with NaOH and there is slight excess of NaOH.

The color change from yellow to blue makes us verify that the reaction is happening.

HCl + NaOH + NaCl + H2O

The reaction stoichiometry is 1 mole of NaOH per mole of HCl.

According to experimental data, the number of moles of NaOH are less than the number of moles of HCl.

This is not reasonable as excess of NaOH is needed for color change from yellow to blue. It can be concluded that the values of 0.1 M for concentrations of HCl and NaOH are incorrect or the number of drops are incorrectly counted.

Note: The concentrations of NaOH and HCl are same at 0.1 M. The number of drops of NaOH are lesser than the number of drops of HCl. This sugghests that number of moles of NaOH are lesser than number of moles of HCl.