Jacob carelessly added only 40.0 mL (instead of the recommended 50.0 mL) of 1.1 M HCl to the 50.0 mL of 1.0 M NaOH. Explain the consequence of the error.

Explanation:

mole of NaOH present = molarity x volume

                                     = 1.0 X 0.05 = 0.05 mole

Recommended mole of HCl = 1.1 x 0.05 = 0.055

Mole of HCl carelessly added by Jacob = 1.1 x 0.04 = 0.044

From the equation of reaction:

HCl + NaOH > NaCl + H2O

The ratio of mole of HCl to that of NaOH for a complete neutralization reaction is 1:1. However, the recommended mole of HCl (0.055 mole) is more than the mole of NaOH (0.05 mole). Hence, the recommended endpoint of the reaction is supposed to be acidic.

The mole of HCl added by Jacob (0.044) is short of the recommended amount (0.055) and also short of the amount required for a neutral endpoint (0.05). This means that the endpoint will have an excess amount of NaOH and as such, basic instead of the desired acidic endpoint.