1. When measuring chemicals in the chemistry laboratory, one can easily recognize if the measurement to be made is critical or not by looking at the instructions that are given. For measurements that are not all that critical, words such as 'approximately or about' are often used when their measurement is been talked about.
For a measurement that is not critical, a good example is when one is adding a particular salt to a solution, so that the crystals of the salt will be formed. All that one have to do in this case, is to use a spatula to scoop salt and pour it inside the salt solution until one observe the formation of free crystals.
2. An example of a chemical reaction that needs careful measurement of reagents is one that involves mixing of two chemicals in order to observe the chemical and the physical change that will occur. In this case, careful measurements have to be made in order to get valid results. A good example of this is when acid and base are titrated against each other in the presence of indicator in order to determine the equivalent point. In this case, precise measurement has to be taken in order to determine the concentration of either the acid or the base.
