Introduction
In the real world, the mixtures and solutions we have and work with often have impurities or multiple different elements and compounds in them. It’s important to understand how samples are organized and named and how the mass and elemental compositions of mixtures change depending on what's in them.
Mixtures and Pure Substances
When you have a sample of matter in chemistry, it can be sorted into two main categories, those being a Mixture or a Pure Substance. Mixtures contain multiple different compounds inside of them, and those compounds are able to be physically separated using a variety of methods. Pure Substances contain only one type of compound/element. Samples containing pure substances are the ones that we analyzed the mass composition of in the previous subunit.
These categories can be split even further. A mixture can either be a homogenous or heterogenous mixture. A homogenous mixture has all of its parts evenly spread out and mixed together, while a heterogenous mixture has its parts not evenly mixed. Homogenous mixtures are simpler to understand, like dissolving sugar in water, where the sugar gets evenly mixed in, and any part of the mixture will look almost exactly the same as any other part. Homogenous mixtures are also the most common that will appear in chemistry under the name solutions. Heterogeneous mixtures can be harder to understand. On a large scale, this can look like a mixture of oil and water, where they are almost completely separated, but some mixtures that seem homogeneous can be heterogeneous, as there are small clumps on a microscopic level, which means if you look close enough some parts will be different than others.
Pure substances are either elements or compounds. Elements, as the name suggests, contains only one type of atom., while compounds contain multiple different elements/atoms which are chemically connected. Another difference between them is that the smallest unit you will work with for elements is an atom, but for compounds it will be a molecule, formula unit, or ion.
Understanding and Calculating with Impurities
The mass and elemental compositions of a sample can change when new compounds and elements are added. If you have a sample of water (), it will be hydrogen by mass and oxygen by mass. If you add hydronium ions () to the water, the percent mass of hydrogen will increase and the percent mass of oxygen will decrease.