Gravimetric Analysis

Have you ever tried to measure the weight of the solid particles suspended in water? Some of you may have done this or something similar to this during your chemistry practicals in school days. Well this process of weighing the substance present in other substance is known as gravimetric analysis in scientific terms. Given below is its scientific definition.

Definition

It is a set of methods used in analytical chemistry for the quantitative determination of an analyte based on the mass of the solid. An analyte is a substance or a chemical element which is determined in an analytical procedure. Analyte is referred as substance that cannot be measured but measurable property of the analyte can be measured. For example, a bed can be considered as an analyte where we cannot really measure the bed but the height, weight, and width, etc.,of the bed can be measured. In short, the analysis allows one to determine the mass of a pure compound to which the analyte is related. For example, it is quite challenging to measure glucose in the blood but one can measure the glucose concentration in blood by using gravimetric factor. The process of this analysis involves, isolating the ions in the substance using precipitation reaction, then filtering and washing the precipitate to remove the impurities, and then converting a precipitation into a measurable compound and then finally weighing it to determine its mass by difference. Now let's see the step wise procedures involved in this analysis.

Procedure for the Analysis

Given below is the standard procedure for determining the mass of a substance using gravimetric method.

• At first you need to weigh the sample or substance that need to be analyzed.
• If the substance is not in the soluble state, then dissolve it in the suitable solvent.
• Now you need to start with precipitating the analyte, for which you have to add an excessive precipitating reagent.
• Once you add the precipitate, filter the whole mixture to isolate the precipitate from the solution.
• There are chances of impurities in the precipitate, so wash the precipitate thoroughly to remove the same.
• Now you have to dry the precipitate. The general method for drying the precipitate is by heating it. The heating process removes the water from the precipitate completely.
• Before the mixture catches any moisture from the surroundings it is ideal to cool it down in a dessicator.
• Now, weigh the cooled substance and note it down on a piece of paper. Repeat the drying and weighing process till you get the constant mass of the precipitate.
• Now, subtract the mass of the crucible from the combined mass, which will give you the mass of the precipitated analyte. Once you get the composition of the precipitate, you can easily calculate the mass of the analyte in the actual sample.

The above analysis procedure needs to be followed very carefully to get the exact measurements. An incomplete precipitation or incomplete drying or cooling can cause errors in finding out the actual mass of the analyte. There are different formulas that can help you carry out the calculations easily. The procedures and formulas are same, be it the analysis of a metal carbonate or soluble chloride. Given below are the steps that would help you calculate the mass accurately.

• First, write the balanced chemical equation for the precipitation reaction.
• Then calculate the moles of the precipitate using this formula: moles = mass/molecular mass
• Using the moles ratio of the analyte, calculate the moles of analyte from the balanced chemical equation.
• Now calculate the mass of the analyte using this formula: mass = moles x molecular mass
• Finally calculate the percentage using this formula: mass of analyte in sample = (mass analyte/mass sample)/100.

This procedure would give you the parentage of a substance present in the total original sample. You may take an assistance of your teacher or lab assistant to conduct the experiment accurately. The above information would be resourceful for you when you would be helping your children to complete their chemistry homework!