Chapter 20, Problem 20.35E

An aqueous reaction that uses the solvent ${\text{H}}_2\text{O}$ as a reactant has a given rate law of

$\text{rate}=k\cdot \left[{\text{H}}_2\text{O}\right]\left[\text{A}\right]$

Where $\text{A}$ is the other reactant species. Explain why, in most circumstances, this reaction can be defined in terms of pseudo first-order kinetics. What are the units on the rate constant?