C150-20230823-Classifying Matter and Changes, Measurements in Chemistry

 We often engage in "sorting" activities where we define a couple of distinct categories and then try to sort a bunch of properties or observations into those categories. Today we did some sorting…

Matter sorting categories:

• Solid/Liquid/Gas - These are the standard states of matter.
• Intensive/Extensive properties - Intensive properties are defined by the identity of the matter, such as density or elemental composition. Extensive properties describe the amount or form of the matter, such as mass or shape.
• Elements/Compounds/Solution/Heterogeneous mixtures - Pure substances can either be elements (if they're just made of 1 type of atom) or compounds (if they are made of multiple types of atoms in faxed ratios). For mixtures, a homogeneous mixture has the same composition throughout (usually called a solution) and a heterogeneous mixture will have varying composition depending upon where it's being sampled (like a chocolate chip cookie).

When we're looking at how matter changes, there are also two important categories for sorting: chemical change or physical change. Chemical change alters the atomic or molecular nature of the system undergoing change, physical change alters its form or state. Melting ice, dissolving sugar in water, and crushing an aluminum can are all physical changes. Burning sugar, tarnishing metal, and baking a cake are all chemical changes.

In order to observe these changes, we often need to measure something. Taking measurements always involves some degree of uncertainty or variability. This is often called "error", but it doesn't necessarily mean that a mistake was made, it just means that every measurement process has some uncertainty. One way that we can include that uncertainty in values we report is by the use of significant figures. There's a more detailed description of sig figs here: https://chembits.com/GenChem/SigFigs2021a.pdf

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