Which piece of equipment could not be used in an experiment to measure the rate of this reaction?

\[{\text{C}}{{\text{H}}_3}{\text{COC}}{{\text{H}}_3}{\text{(aq)}} + {{\text{I}}_2}{\text{(aq)}} \to {\text{C}}{{\text{H}}_3}{\text{COC}}{{\text{H}}_2}{\text{I (aq)}} + {{\text{H}}^ + }{\text{(aq)}} + {{\text{I}}^ - }{\text{(aq)}}\]

A.     A colorimeter

B.     A gas syringe

C.     A stopwatch

D.     A pH meter

B