Unit 1: Matter and Measurement
What matter actually is, how chemists sort it, and the counting and measuring skills every later unit leans on.
10 topics · 39 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
1.1 States of Matter and the Particle Model
- How it worksHow do the particles in a solid, a liquid, and a gas actually move differently?
- How it worksHow does heating a solid make its particles break free into a liquid?
- Common mistakeWhy doesn't a gas have a fixed shape the way a solid does?
- Going furtherWhat happens to the spacing between particles when a gas is squeezed into a smaller container?
- Ties togetherHow does the same particle-motion picture that explains melting and boiling also explain why a gas presses outward on the walls of its container?
Your turn1 of 2
Ice, liquid water, and steam look completely different, one hard and solid, one flowing, one an invisible gas, yet chemists insist all three are exactly the same substance. Why does ice, liquid water, and steam all count as the exact same substance?1.2 Classifying Matter: Pure Substances and Mixtures
- How it worksHow do you sort a sample of matter into a pure substance or a mixture?
- How it worksHow does a homogeneous mixture differ from a heterogeneous one at the particle level?
- Common mistakeWhy isn't air a pure substance even though it looks like one thing?
- Going furtherWhat happens to how you classify a mixture once you can no longer see its separate parts?
Your turn1 of 2
Table salt alone is classified as a pure substance, but the moment you dissolve that same salt into water, the resulting salt water is classified as a mixture instead. Why does salt water count as a mixture but table salt alone does not?1.3 Elements, Compounds, and Mixtures
- How it worksHow do atoms of two different elements combine to make a brand new compound?
- How it worksHow does separating a mixture differ from breaking apart a compound?
- Common mistakeWhy isn't a compound just a mixture of the elements that make it up?
- Worked exampleFind how many different elements are present in one molecule of glucose, C6H12O6.
Your turn1 of 2
A single molecule of a compound contains 14 carbon atoms, 26 hydrogen atoms, and 19 oxygen atoms. How many total atoms does one molecule of this compound contain?1.4 Physical Properties of Matter
- How it worksHow do properties like melting point and density let a chemist identify an unknown substance?
- Common mistakeWhy isn't color always a reliable physical property for identifying a substance?
- Going furtherWhat happens to a substance's physical properties when it changes from a solid to a liquid?
Your turn1 of 2
A chemist can often tell a sample is a metal just by its characteristic shine, without running any chemical test on it at all. Why can you identify a metal by its shine without doing any chemistry to it?1.5 Physical versus Chemical Change
- How it worksHow do you tell whether a new substance has actually formed after a change?
- Common mistakeWhy isn't melting ice a chemical change even though the water clearly transforms?
- Going furtherWhat happens to a piece of iron the moment it starts to rust?
- How it worksWalk me through sorting boiling water, rusting a nail, dissolving sugar, and burning wood into physical or chemical change.
Your turn1 of 2
Tearing a sheet of paper into pieces and burning that same sheet of paper both destroy its original intact form, yet chemists classify these as two fundamentally different kinds of change. Why does tearing paper count as a different kind of change than burning it?1.6 Signs of a Chemical Reaction
- How it worksHow does a temperature change during a reaction reveal that bonds are being broken and formed?
- Common mistakeWhy isn't every color change or every bubble proof that a chemical reaction happened?
- Going furtherWhat happens when you mix baking soda with vinegar that tells you a reaction occurred?
Your turn1 of 2
Watching two substances mix and suddenly bubble vigorously, or shift dramatically from clear to bright yellow, immediately signals to a chemist that something chemically significant just happened. Why does bubbling or a sudden color change tip you off that a new substance has appeared?1.7 SI Units and the Metric System
- How it worksHow do metric prefixes like kilo, centi, and milli scale a base unit up or down?
- Worked exampleFind how many milliliters are in 2.5 liters of a solution.
- Common mistakeWhy isn't a kilogram actually a unit of weight?
- Going furtherWhat happens to how precise a measurement looks when you switch from meters to millimeters?
Your turn1 of 2
Find how many milliliters are in 27.87 liters of a solution.1.8 Dimensional Analysis and Unit Conversion
- How it worksHow do conversion factors cancel out unwanted units step by step?
- Worked exampleFind how many seconds are in 3.5 hours using dimensional analysis.
- Worked exampleWalk me through converting 15 miles per hour into meters per second.
- Common mistakeWhy doesn't skipping the units during a conversion still get you the right answer?
Your turn1 of 2
Find how many seconds are in 20.92 hours using dimensional analysis.1.9 Significant Figures
- How it worksHow do you decide which digits in a measured number actually count as significant?
- Worked exampleFind the correct number of significant figures in the measurement 0.00420 grams.
- Worked exampleWalk me through multiplying 4.52 cm by 3.1 cm and rounding to the right number of sig figs.
- Common mistakeWhy doesn't a calculator's full string of decimal digits belong in your final answer?
Your turn1 of 2
A rectangular sample measures 14 cm by 13 cm, each measured to the precision shown. What is the sample's area, in square centimeters?1.10 Density as a Physical Property
- How it worksHow does packing more mass into the same volume raise a substance's density?
- Worked exampleFind the density of a 45 gram block of metal that displaces 5 mL of water.
- Common mistakeWhy doesn't a heavier object always have a higher density than a lighter one?
- Going furtherWhat happens to a substance's density when it's heated and its volume expands?
Your turn1 of 2
A block of metal has a mass of 630 grams and displaces 65 mL of water when submerged. What is the metal's density, in grams per milliliter?