Density & Specific Gravity Reference Cheat Sheet

Key Facts

• Density is calculated with $D = \frac{m}{V}$, where mass is usually measured in $\mathrm{g}$ and volume in $\mathrm{mL}$ or $\mathrm{cm^3}$.
• Mass can be found from density using $m = D V$ when density and volume are known.
• Volume can be found from density using $V = \frac{m}{D}$ when mass and density are known.
• Specific gravity is calculated with $SG = \frac{D_{\text{substance}}}{D_{\text{water}}}$ and has no units because the density units cancel.
• For most chemistry problems, water has density $D_{\text{water}} = 1.00\,\mathrm{g/mL}$ at about $4\,^{\circ}\mathrm{C}$, so $SG \approx D$ when density is in $\mathrm{g/mL}$.
• An object floats in a liquid if $D_{\text{object}} < D_{\text{liquid}}$ and sinks if $D_{\text{object}} > D_{\text{liquid}}$.
• Immiscible liquids form layers with the least dense liquid on top and the most dense liquid on bottom.
• Gas density can be calculated from molar mass using $D = \frac{PM}{RT}$, where $P$ is pressure, $M$ is molar mass, $R$ is the gas constant, and $T$ is temperature in kelvin.

Vocabulary

Density

Density is the amount of mass in a given volume, calculated with $D = \frac{m}{V}$.

Mass

Mass is the amount of matter in a sample, commonly measured in $\mathrm{g}$ or $\mathrm{kg}$.

Volume

Volume is the amount of space a substance occupies, commonly measured in $\mathrm{mL}$, $\mathrm{L}$, or $\mathrm{cm^3}$.

Specific Gravity

Specific gravity is the ratio of a substance’s density to the density of water, calculated with $SG = \frac{D_{\text{substance}}}{D_{\text{water}}}$.

Buoyancy

Buoyancy is the upward force a fluid exerts on an object, which helps determine whether the object floats or sinks.

Miscible

Miscible substances mix evenly with each other, while immiscible substances separate into layers.