Observed in Illinois on the first Monday of March every year, the holiday ostensibly honors Polish-born Revolutionary War cavalry officer Casimir Pulaski, though for most school kids with a four-day week, itâs probably just another sweet, sweet sleep-in day.
Yes, in chemistry a pure substance means either an element or a compound. Thus, hydrogen, oxygen, sodium, iron, copper etc. are pure substances; and so are compounds such as water, sugar, ammonia, sodium chloride, methane, ethanol etc. A compound is composed of two or more elements combined in a fixed ratio by mass. Like an element, a compound also has a distinct chemical identity. A mixture is not a pure substance as it is a collection of two or more elements/compounds in varying ratio. Air, sea water, gasoline, vegetable oils, steel etc. are mixtures.
One such form is ammonia (NH3). Ammonia may be taken up by plants or oxidized by bacteria into nitrate (NO3-) or nitrite (NO2). Ammonia (NH3+) is a colorless gas with a strong pungent odor. Ammonia will react with water to form a weak base. The term ammonia refers to two chemical species which are in equilibrium in water (NH3, un-ionized and NH4+, ionized). Tests for ammonia usually measure total ammonia (NH3 plus NH4+).