Impure means mixed with something unwanted or contaminated with foreign substances. When scientists work with impure chemicals, those chemicals contain traces of other materials that shouldn't be there. When a metal is impure, it has other elements mixed in that weaken it or change its properties.

Water from a pond is impure because it contains dirt, bacteria, and tiny organisms floating in it. That's why hikers carry filters or purification tablets to make wild water safe to drink. Pure gold is soft and valuable, but impure gold mixed with copper or silver becomes harder and less precious.

The word also describes something morally tainted or corrupted. In stories, an impure heart might be one filled with selfish motives mixed in with good intentions. Religious traditions often use this word to describe thoughts or actions that fall short of their ideals.

In chemistry and manufacturing, purity matters enormously. Computer chips require incredibly pure silicon because even microscopic impurities can ruin their function. Medieval alchemists spent lifetimes trying to purify substances, believing that removing impurities could transform ordinary metals into gold. While they never succeeded, their efforts helped create modern chemistry and our understanding of why purity matters in science.