# When 1 mol of NaBH4 is used to reduce ketone, how many moles of hydride is used?

The common metal hydride reducing agents, lithium aluminum hydride, $L i A l {H}_{4}$, and sodium borohydride, $N a B {H}_{4}$, are often used 1:1. That is, for a ketone, $R C \left(= O\right) R '$, 1 equiv of reducing agent is added (this means that there may 3 equiv hydride left unreacted.
When you are doing large scale reductions (i.e. when you are trying to reduce $\frac{1}{2}$ a mol of something or more), often you have problems when you add such copious amounts of hydride reagent, because you have to work the reaction mixture up with water, and generate a shed load of hydrogen.