Percent Purity
Definition and meaning of Percent Purity in chemistry.
Percent purity tells us how much of a target chemical is present in a messy, impure sample. It compares the mass of the actual pure substance to the total mass of the entire sample. We express this ratio as a percentage to clearly show the quality of the material.
In more detail
In high school chemistry problems, we often pretend that every chemical comes in a perfectly pure form. However, real life is much messier than a textbook. When scientists dig raw metal ores out of the ground, those rocks are full of dirt and unwanted minerals.
Even when chemists make a new medicine in a spotless lab, the chemical reaction always creates some useless side products. Because of this, raw materials are almost never one hundred percent pure. Percent purity measures exactly what fraction of the sample is the good stuff we actually want.
To find it, you divide the mass of the pure chemical by the total mass of the messy sample. Then, you just multiply that decimal by one hundred. Many students mistakenly use the entire impure mass when trying to calculate a chemical reaction yield.
You must always multiply the total mass by the percent purity first. This step strips away the useless junk and gives you the true mass of the reactive chemical. Checking percent purity is a massive part of daily quality control for factories. Pharmaceutical companies must prove their drugs have an extremely high percent purity before selling them to patients.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Math formula | (Mass of pure chemical / Total mass of sample) × 100 |
| Main purpose | Quality control and checking raw materials |
| Chemical impact | Impurities can ruin sensitive chemical reactions |
| Real world use | Ensuring medicines are safe for human use |
Imagine a mining company digs up a 50.0 gram chunk of raw iron ore. After crushing and testing the rock, they find it contains exactly 32.0 grams of pure iron. By dividing 32.0 by 50.0 and multiplying by 100, they find the rock has a 64.0 percent purity.
Frequently asked questions
Why are chemical samples rarely 100 percent pure?
Chemical reactions often make side products that mix with the final chemical. It is also very difficult to remove all the dust and moisture from the air.
How does percent purity affect stoichiometry calculations?
You cannot use the total weight of an impure rock in a math equation. You must calculate the pure mass first so you only count the actual reacting molecules.
What happens if a factory ignores percent purity?
A factory might accidentally add too little of a vital chemical to a product. In the pharmaceutical industry, this could cause a pill to have the wrong medicine dosage.