# Unit A

## What is Chemistry?

I answer the question “What is Chemistry?” to begin our series of videos in the course.

## Observation vs. Inference

I explain the subtle but important difference in observations and inferences. Observations are statements of observable fact; inferences are conclusions drawn from observations and previous experience.

## Matter Classification

I explain how we describe pure matter: atoms, elements, molecules, and compounds.

## Properties of Matter

There are a few ways to describe matter and how it changes. This video covers physical vs. chemical properties and changes.

## Significant Figures

When we do math with measurements, we often need to round the final answer to contain a certain number of significant figures. In this video, we look at how to determine the number of significant figures in a measurement.

## Rounding

When we do math with measurements, we often need to round the final answer to contain a certain number of significant figures. In this video, we look at how to round measurements to varying numbers of significant figures.

## Measurement Math

When we do math with measurements, we often need to round the final answer to contain a certain number of significant figures. In this video, we look at how to determine the number of significant figures needed in our final calculation.

## Density

Density is one of the most basic concepts in chemistry: mass per volume. Or stuff per space. In this video, we explore the density concept, its equation, a sample calculation, and one purpose behind using density…to identify a substance.

## Percent Error

How good is your result? Percent Error is the best way to express that information. In this video, I explain how to do it.

## Factor-Label Method (Dimensional Analysis)

Also known as dimensional analysis, factor-label method is used to convert a value from one unit into another using conversion factors.