Si unit

Fundamental Units of Measure SI units Stands for Système International d’Unités. These are the internationally agreed on units for measurements. Imagine that you find the following instructions in a laboratory procedure: “Transfer 1.5 of your sample to a 100 volumetric flask, and dilute to volume.” How do you do this? Clearly these instructions are incomplete since the units of measurement are not stated. Compare this with a complete instruction: “Transfer 1.5 g of your sample to a 100-mL volumetric flask, and dilute to volume.” This is an instruction that you can easily follow. Measurements usually consist of a unit and a number expressing the quantity of that unit. Unfortunately, many different units may be used to express the same physical measurement. For example, the mass of a sample weighing 1.5 g also may be expressed as 0.0033 lb or 0.053 oz. For consistency, and to avoid confusion, scientists use a common set of fundamental units, several of which are listed in Table 2.1. These units are called SI units after the Système International d’Unités. Other measurements are defined using these fundamental SI units. For example, we measure the quantity of heat produced during a chemical reaction in joules, (J), whe