States of matter and mixtures

Welcome to States of Matter and Mixtures!

In this chapter, we are going to explore what the world is made of and how we can "un-mix" things. Whether it's turning sea water into drinking water or figuring out if a food dye is made of one color or many, Chemistry gives us the tools to do it. Don't worry if this seems like a lot of information at first—we will break it down into tiny, easy-to-understand pieces.

1. The Three States of Matter

Everything around you is made of particles. Depending on how much energy these particles have, they behave in three different ways: Solid, Liquid, and Gas.

Particle Arrangement and Movement

Solids: Imagine a crowd of people sitting in theater seats. They are packed very close together in a regular lattice arrangement. They can't move around, so they just vibrate in fixed positions. They have the lowest energy of the three states.

Liquids: Now imagine those people standing up and walking around a crowded room. They are still close together and touching, but they are in a random arrangement and can flow over each other. They have more energy than solids.

Gases: Imagine people running around a massive football field. The particles are far apart, move randomly at high speeds, and have the highest energy.

Predicting the State of a Substance

You can predict if something is a solid, liquid, or gas if you know the temperature and its melting and boiling points.

1. If the temperature is below the melting point, it is a Solid.
2. If the temperature is between the melting and boiling points, it is a Liquid.
3. If the temperature is above the boiling point, it is a Gas.

Quick Review:
- Solid: Regular, vibrating, low energy.
- Liquid: Random, flowing, medium energy.
- Gas: Far apart, fast-moving, high energy.

2. Changing State

When we heat or cool substances, they change state. These are physical changes. This means no new substances are made, and the change can be reversed (like melting ice and then freezing it again).

The Interconversions

- Melting: Solid to Liquid.
- Evaporating/Boiling: Liquid to Gas.
- Condensing: Gas to Liquid.
- Freezing: Liquid to Solid.
- Sublimation: Solid to Gas (skipping the liquid stage!).

What happens to the particles?
When you heat a solid, the particles gain energy and vibrate faster. Eventually, they have enough energy to break away from their fixed positions—this is melting. When you cool a gas, the particles lose energy and move slower, allowing forces of attraction to pull them back together—this is condensing.

Did you know? Your phone screen uses "Liquid Crystals"—a state of matter that flows like a liquid but has particles arranged somewhat like a solid!

3. Pure Substances vs. Mixtures

In everyday life, we might say orange juice is "pure," but in Chemistry, that’s not true! Pure orange juice is actually a mixture of water, sugar, vitamins, and acid.

The Chemistry Definition

Pure Substance: Contains only one type of element or one type of compound. It has a sharp melting point (it melts at exactly one temperature).
Mixture: Contains two or more substances that are not chemically joined. Mixtures melt over a range of temperatures.

Common Mistake to Avoid: On an exam, if a graph shows a substance melting over a slanted line (e.g., from \(55^\circ C\) to \(60^\circ C\)), it is a mixture. If the line is perfectly flat at one temperature, it is pure.

4. Separation Techniques

How do we get the stuff we want out of a mixture? We use their physical properties!

Filtration

Used to separate an insoluble solid (a solid that won't dissolve) from a liquid. Think of it like using a sieve for pasta. The liquid passes through the paper (the filtrate), and the solid gets stuck (the residue).

Crystallisation

Used to separate a soluble solid (like salt) from a liquid. We heat the solution to evaporate some water until it's saturated, then let it cool. As it cools, crystals of the solid form.

Simple Distillation

Used to separate a liquid from a solution (e.g., getting pure water from salt water). We boil the mixture, the water turns into steam, and we catch that steam in a condenser, which cools it back into pure liquid water. The salt stays in the flask.

Fractional Distillation

Used to separate a mixture of liquids with different boiling points (like crude oil or alcohol and water). We use a fractionating column. The liquid with the lowest boiling point reaches the top of the column and is collected first.

Memory Aid: Fractional = Fractions. We are splitting the mixture into different parts or "fractions."

5. Paper Chromatography

This is a cool way to separate mixtures of soluble substances, like the different dyes in ink.

How it works

1. Stationary Phase: This is the paper. It doesn't move.
2. Mobile Phase: This is the solvent (like water or ethanol) that moves up the paper.

Substances that are more soluble in the solvent move further up the paper. Substances that stick more to the paper stay lower down.

Interpreting a Chromatogram

- A pure substance will only produce one spot.
- An impure substance (mixture) will produce two or more spots.
- If two spots are at the same height, they are likely the same substance.

Calculating \(R_f\) Values

The \(R_f\) value is a ratio that helps us identify a substance. It is always a number between 0 and 1.

\(R_f = \frac{\text{distance moved by the substance}}{\text{distance moved by the solvent}}\)

Quick Review Box:
- Filtration: For insoluble solids.
- Distillation: For liquids with different boiling points.
- Chromatography: For soluble dyes/inks.

6. Making Water Safe to Drink

Water from rivers or the sea isn't safe yet. It needs to be potable (safe for drinking).

Ground Water Treatment

1. Sedimentation: Let the water sit so big bits of dirt sink to the bottom.
2. Filtration: Pass the water through sand and gravel to catch smaller bits of dirt.
3. Chlorination: Add chlorine gas to kill dangerous bacteria and microbes.

Sea Water Treatment

Sea water has too much salt. We make it potable by distillation. However, this uses a lot of energy, so it is very expensive!

Water for Analysis

In a science lab, we use distilled water or deionised water. Normal tap water contains dissolved ions (like calcium) that could mess up our experiments. Water for analysis must not contain any dissolved salts at all!

Key Takeaway: Clean drinking water (potable) is not the same as chemically pure water. Potable water still has some dissolved minerals that are good for us, while water for analysis must be 100% \(H_2O\).