Week 5, Session 14: Matter — States, Properties, Density, Mixtures, and Solutions

Week 5, Session 14: Matter — States, Properties, Density, Mixtures, and Solutions

Why this session matters

Matter is anything that has mass and takes up space — which is everything physical. The GED® asks you to compare the states of matter, use density to predict floating and sinking, and tell a physical change from a chemical one. These show up as both facts and quick calculations.

The big idea in plain words

The same stuff can look completely different depending on how fast its particles move. Cold and slow, particles lock into a solid. Warmer, they loosen into a liquid. Hot and fast, they fly apart into a gas. Whether something floats comes down to density — how much mass is packed into its space.

Picture it

Words you must own

• Matter: anything with mass and volume.
• Density: how much mass fits in a volume: \(\text{density}=\dfrac{m}{V}\).
• Solid / liquid / gas: the three common states (particle motion differs).
• Melting / freezing / evaporation / condensation / sublimation: the state changes.
• Physical property: observed without changing what it is (color, density, melting point).
• Chemical property: how it reacts to form new substances (flammable, rusts).
• Physical change: no new substance (melting ice, cutting paper).
• Chemical change: a new substance forms (burning, rusting).
• Mixture: substances physically combined and separable (salt water, air).
• Solution: a mixture where one substance (solute) dissolves evenly in another (solvent).

The science, step by step

1. States and particle motion: solids hold shape (particles vibrate in place); liquids flow (particles slide); gases fill any container (particles fly apart).
2. Adding heat speeds particles up and drives changes: solid → liquid (melting) → gas (evaporation/boiling). Removing heat reverses them.
3. Density predicts floating: an object floats in water if its density is less than 1 g/mL; it sinks if greater.
4. Physical vs chemical: a physical change alters form but not identity; a chemical change makes something new (often with a color change, gas, or temperature change).
5. Mixtures vs pure substances: mixtures can be separated by physical means (filtering, evaporating); a solution is a mixture that looks uniform throughout.

Exam-style passage

Passage. A student measured the mass and volume of three solid blocks, then tested each in a tank of water (water's density is 1.0 g/mL).

Watch me solve one

Question about the passage: Find each block's density and predict which block floats in water.

• READ: Density = mass ÷ volume for each block.
• CHOOSE: A: \(20/10 = 2.0\) g/mL. B: \(8/10 = 0.8\) g/mL. C: \(30/30 = 1.0\) g/mL. Water is 1.0 g/mL, so Block B (0.8) floats, Block A (2.0) sinks, and Block C (1.0) neither rises nor sinks.
• CHECK: The rule holds: less dense than water floats; denser sinks; equal density hovers.

10 Guided Examples (cover the answer, then check)

Examples 1–5 use the three-block passage.

1. Density A. What is Block A's density?
   Answer: 2.0 g/mL.
   Why: 20 ÷ 10 = 2.0.
2. Density B. What is Block B's density?
   Answer: 0.8 g/mL.
   Why: 8 ÷ 10 = 0.8.
3. Float. Which block floats in water?
   Answer: Block B.
   Why: 0.8 g/mL is less than water's 1.0 g/mL.
4. Neutral. What happens to Block C?
   Answer: It neither floats nor sinks.
   Why: Its density (1.0) equals water's.
5. Compare. Which block is densest?
   Answer: Block A.
   Why: 2.0 g/mL is the largest density.
6. State. In which state do particles vibrate in place but stay packed?
   Answer: Solid.
   Why: Solids hold a fixed shape.
7. Change. Is melting ice a physical or chemical change?
   Answer: Physical.
   Why: It is still water, just a different state.
8. Change. Is burning wood physical or chemical?
   Answer: Chemical.
   Why: New substances (ash, gases) form.
9. Mixture. Is salt water a mixture or a pure substance?
   Answer: A mixture (a solution).
   Why: The salt is dissolved and can be separated by evaporation.
10. Solute/solvent. In salt water, what is the solute and what is the solvent?
    Answer: Salt is the solute; water is the solvent.
    Why: The solute dissolves in the solvent.

The traps GED® loves

• Bigger mass = always sinks? No — floating depends on density (mass per volume), not mass alone.
• Dissolving is a chemical change? No — dissolving salt is physical; the salt is still salt and can be recovered.
• Boiling changes the substance? No — boiling water makes water vapor, still water (physical change).
• All mixtures look uneven? A solution is a mixture that looks uniform, but it is still a mixture.

Quick Check

Your practice — 10 questions

Answer from memory (calculator fine). For float/sink, compute density then compare with 1.0 g/mL.

Before you move on

• Sketch particle spacing for solid, liquid, and gas.
• Compute the density of a 50 g, 25 mL object (2.0 g/mL) and say if it floats.
• Score at least 8 of 10 before Session 15.