Physical Properties — Density, Solubility, Conductivity
In 1912, the RMS Titanic — a 46,000-tonne steel ship — sank after hitting an iceberg, while that same frozen water floated: three physical properties (density, solubility, conductivity) explain everything strange about that night.
Printable Worksheets
Print or save as PDF — or build a custom worksheet from any module's questions.
Q1 · A 1 kg block of feathers and a 1 kg block of lead are placed on a scale together. Which has the larger volume, and why?
Q2 · Why are saucepans usually metal but their handles wooden or plastic? Use the word "heat" in your answer.
● Know
- What density, solubility and conductivity mean
- Common units (g/cm³ for density)
- That metals are generally good conductors, non-metals usually aren't
● Understand
- Why something less dense than water floats
- Why ice is less dense than liquid water (the floating ice puzzle)
- How property data lets us identify an unknown substance
● Can do
- Use the density formula d = m / V (no maths beyond simple division)
- Predict whether something will float or sink
- Read a property table and identify a likely substance
- Density
- Solubility
- Conductor
- Insulator
- Physical property
- Feature you can measure without changing the substance
- How much of a substance can dissolve in a liquid
- Mass divided by volume (g/cm³)
- Material that blocks heat or electricity
- Material that lets heat or electricity through easily
Drop a grape into a glass of water — it sinks. Drop a grape into a glass of fizzy lemonade — it bobs up and down. The grape hasn't changed; the liquid has. What changed is how much "stuff" is packed into each mL of liquid, which is exactly what density measures. The formula is:
density = mass ÷ volume (d = m / V)
Units are usually grams per cubic centimetre (g/cm³). Water has a density of 1.0 g/cm³ — handy because it gives us a benchmark:
- If something is less dense than water (under 1.0 g/cm³), it floats.
- If something is more dense than water (over 1.0 g/cm³), it sinks.
| Substance | Density (g/cm³) | In water? |
|---|---|---|
| Cork | 0.24 | Floats |
| Ice | 0.92 | Floats |
| Water (liquid) | 1.00 | — |
| Aluminium | 2.70 | Sinks |
| Iron | 7.87 | Sinks |
| Gold | 19.30 | Sinks |
That's how a battleship floats — even though steel is dense, the ship's huge hull is mostly air, so its average density (steel + air) is less than water. Pack the ship with too much cargo and it sinks.
For almost every substance, the solid form is more dense than its liquid form — particles in a solid are packed tighter, so they take less space. But water breaks the rule.
When water freezes, the particles arrange themselves into a six-sided crystal pattern with surprisingly large gaps. Ice particles take up more space than liquid water particles, so ice is less dense than water (0.92 g/cm³ vs 1.0 g/cm³) — and floats.
This is a huge deal for life on Earth:
- In winter, a lake freezes from the top down. Floating ice forms a lid that keeps the warmer liquid water underneath protected.
- Fish, frogs and aquatic plants survive winter under the ice — the ice insulates them.
- If ice were denser, lakes would freeze from the bottom up and most freshwater life would be wiped out every winter.
One quirky physical property of water keeps half the planet's freshwater ecosystems alive. Not bad.
Ice is dense than liquid water because the particles arrange in a crystal with big . So ice . This is unusual — most solids are dense than their liquid form.
If you stir sugar into your tea, it disappears — but the tea still tastes sweet. The sugar has dissolved. Stir sand into water and it sits at the bottom. The sand has not dissolved.
Solubility is how much of a substance will dissolve in a liquid (called the solvent, usually water in school chemistry).
| Substance | Dissolves in water? | Why it matters |
|---|---|---|
| Table sugar (sucrose) | Yes — a lot | Makes a sweet drink |
| Table salt (sodium chloride) | Yes — a lot | Why seawater is salty |
| Beach sand | No | Stays at the bottom of a glass |
| Cooking oil | No — separates | Italian dressing has to be shaken |
| Carbon dioxide gas | A small amount | How fizzy drinks get their bubbles |
Solubility usually increases with temperature for solids — that's why hot chocolate dissolves faster than cold. It's the opposite for gases — that's why a warm fizzy drink loses its bubbles quickly.
Some substances let heat or electricity flow through them; others block it. The flowing kind are called conductors; the blocking kind are insulators.
| Material | Heat conductor? | Electrical conductor? | Used for |
|---|---|---|---|
| Copper | Yes (very) | Yes (very) | Power wires, saucepan bases |
| Aluminium | Yes | Yes | Drink cans, cookware |
| Wood | No | No | Spoon handles, surfboards |
| Plastic | No | No | Wire coatings, electric kettle handles |
| Glass | Mostly no | No | Window panes (insulator) |
Pattern to remember: metals are almost always good conductors (both heat and electricity). Non-metals are almost always insulators. The big exception is graphite (a form of carbon in pencil leads) — it's the rare non-metal that conducts electricity, which is why it's used in batteries.
That's why your saucepan is metal (to spread the heat from the stove) but the handle is plastic or wood (so you can hold it without burning your hand). And it's why power cables have a copper core wrapped in plastic — copper carries the electricity, plastic stops it touching you.
Each substance has its own unique combination of physical properties. By measuring a few of them you can often work out what a mystery substance is.
| Substance | Density (g/cm³) | Melting point (°C) | Soluble in water? |
|---|---|---|---|
| Aluminium | 2.70 | 660 | No |
| Iron | 7.87 | 1538 | No |
| Gold | 19.30 | 1064 | No |
| Table salt (NaCl) | 2.16 | 801 | Yes |
| Sugar (sucrose) | 1.59 | 186 (decomposes) | Yes |
Worked example. A silvery-grey lump has a density of 7.9 g/cm³, melts above 1500 °C and doesn't dissolve in water. Which substance is it most likely?
Iron. The density and high melting point match iron exactly. Aluminium is much less dense, gold is far denser, and the two soluble ones are ruled out.
Olive oil (density 0.92 g/cm³), water (1.0 g/cm³) and honey (1.42 g/cm³) are carefully poured into the same tall glass. Predict the order they will end up in (top to bottom) and explain why.
How close was your prediction?
Nice — you stacked the liquids in order of density.
Good to spot the pattern — less dense always sits above more dense.
At the start of this lesson you were asked: Ice is the solid form of water — so why on Earth does it float on top of the liquid? Think back to what you guessed before the lesson.
Now that you've learned about density, write a proper explanation. Use the words density, less dense and structure to explain why ice floats — and why that is actually very unusual for a solid.
Q1. Define density, solubility and conductivity in your own words. Give a one-line example for each. (3 marks)
Q2. Explain why a battleship made of steel can float on water, even though a small steel nail sinks. Use the word "density" in your answer. (4 marks)
Q3. A student finds an unknown metal at the beach. It is silvery, doesn't rust easily, has a density of about 2.7 g/cm³, and conducts heat very well. Using property data, identify the metal and explain how you used at least two pieces of evidence. (4 marks)
Answers
▾MCQ 1
A — Olive oil (0.92 g/cm³) is less dense than water (1.0 g/cm³) so it floats. It also doesn't dissolve in water, so it sits as a separate layer on top.
MCQ 2
C — Plastic is a heat insulator, so it doesn't conduct heat from the pan to your hand. All the metal choices would burn you.
MCQ 3
D — Ice is less dense than liquid water because its particles arrange into a crystal pattern with bigger gaps. Less dense things float on more dense things.
MCQ 4
B — Whether something dissolves in water is a measure of its solubility. Sugar has high solubility, sand has zero.
MCQ 5
C — Gold matches all three clues: density 19.3 g/cm³ (very dense), melting point 1064 °C, and doesn't dissolve in water. The colour (shiny yellow) is a bonus clue.
Short Answer 1
Model answer: Density = how much mass is packed into a given volume (mass ÷ volume). Example: gold is very dense (19.3 g/cm³) — a small block is very heavy. Solubility = how much of a substance can dissolve in a liquid. Example: sugar dissolves easily in tea, beach sand doesn't. Conductivity = how well a substance lets heat or electricity flow through it. Example: copper wire conducts electricity well; plastic insulates it.
Short Answer 2
Model answer: A small steel nail is denser than water (steel ≈ 7.9 g/cm³, water = 1.0 g/cm³), so it sinks. A battleship is mostly empty inside — full of air, fuel and rooms — so its average density (the total mass of steel + air divided by the total volume of the hull) is less than 1.0 g/cm³. Because the ship's average density is lower than water's density, it floats. Overload the ship with too much cargo and the average density rises, which is how ships sink.
Short Answer 3
Model answer: The metal is most likely aluminium. Two pieces of evidence: (1) The density of 2.7 g/cm³ matches aluminium exactly from the property table — iron (7.87) and gold (19.3) are far denser. (2) Aluminium is well known as a heat conductor (used in saucepans and drink cans). It also doesn't rust like iron, which fits "doesn't rust easily". Together these three clues make aluminium by far the best match.