# How is density used in chemistry?

$\text{Density } \rho$ $=$ $\text{Mass"/"Volume}$
Thus $\text{Mass}$ $=$ $\text{density "xx" volume}$.
And thus a stoichiometric mass of chemical can be introduced by delivery of a known volume of reagent. The reagent necessarily must be a fluid, i.e. a gas, or more generally, a liquid. $5 - 10 \cdot m L$ syringes (and smaller and larger volumes) are routinely used by by synthetic chemists to withdraw given volumes of air-sensitive reagent. The syringes are typically purged first a couple of times with inert gas, so that the atmosphere does not react with the reagent during transfer.