UNITS AND THEIR USE IN CALCULATIONS

Most numbers used in chemistry are accompanied by a unit that tells the type of quantity that the number expresses and the smallest whole portion of that quantity. For example, 36 liters denotes that a volume is expressed and the smallest whole unit of the volume is 1 liter. The same quantity could be expressed as 360 deciliters, where the number is multiplied by 10 because the unit is only 1/10 as large. 

Except in cases where the numbers express relative quantities, such as atomic masses relative to the mass of carbon-12 or specific gravity, it is essential to include units with numbers. In addition to correctly identifying the type and magnitude of the quantity expressed, the units are carried through mathematical operations. The wrong unit in the answer shows that something has been done wrong in the calculation and it must be checked. 

---