Which of the following is a pure substance rather than a mixture?
Air
Brass
Distilled water
Seawater
Tap an answer to check it.
WhyA pure substance has a fixed composition. Distilled water is the compound $\text{H}_{2}\text{O}$ only. Air, brass and seawater are all mixtures of two or more substances.
2Multiple choice · Easy
What is a temperature of $25\,^{\circ}\text{C}$ expressed on the Kelvin scale?
$248\,\text{K}$
$273\,\text{K}$
$298\,\text{K}$
$323\,\text{K}$
Tap an answer to check it.
WhyTo convert from Celsius to Kelvin add 273: $T(\text{K}) = 25 + 273 = 298\,\text{K}$.
3Multiple choice · Medium
The direct change of state from a gas to a solid without passing through the liquid state is called:
Sublimation
Deposition
Condensation
Freezing
Tap an answer to check it.
WhyDeposition is gas to solid directly. Sublimation is the reverse (solid to gas). Condensation is gas to liquid and freezing is liquid to solid.
4Multiple choice · Medium
According to kinetic molecular theory, when the temperature of a gas is increased its particles:
Move faster on average
Lose mass
Become larger
Stop colliding
Tap an answer to check it.
WhyTemperature is a measure of the average kinetic energy of particles. Higher temperature means greater average kinetic energy, so the particles move faster on average.
5Multiple choice · Medium
Which technique is best for separating two completely miscible liquids that have different boiling points?
Filtration
Fractional distillation
Decanting
Using a separating funnel
Tap an answer to check it.
WhyFractional distillation separates miscible liquids by exploiting differences in boiling point. Filtration separates insoluble solids; a separating funnel separates immiscible liquids.
6Multiple choice · Hard
A substance has a fixed composition and can only be broken down into simpler substances by chemical reactions. It is best classified as:
An element
A compound
A homogeneous mixture
A heterogeneous mixture
Tap an answer to check it.
WhyA compound has a fixed composition and is broken down by chemical means into its elements. An element cannot be broken down chemically; mixtures have variable composition and are separated physically.
7Fill in the blank · Easy
The temperature at which a solid turns into a liquid is called the point.
Answer:
melting / melting point
WhyAt the melting point the solid and liquid states coexist; thermal energy overcomes the forces holding particles in the fixed lattice.
8Fill in the blank · Medium
Absolute zero, the lowest possible temperature, is $0\,\text{K}$, which is equal to $^{\circ}\text{C}$ (to the nearest whole number).
Answer:
-273 / -273.15
WhyThe Kelvin and Celsius scales are offset by 273. Therefore $0\,\text{K} = 0 - 273 = -273\,^{\circ}\text{C}$ (more precisely $-273.15\,^{\circ}\text{C}$).
9Multiple choice · Medium
A test tube contains a mixture of miscible liquid hydrocarbons. What type of mixture is it and how is it best separated?
Homogeneous, separated by distillation
Heterogeneous, separated by filtration
Homogeneous, separated by filtration
Heterogeneous, separated by distillation
Tap an answer to check it.
WhyMiscible liquids form a single phase, a homogeneous mixture, best separated by fractional distillation using their differing boiling points.
10Multiple choice · Easy
Which property is used to separate a mixture of miscible liquids by distillation?
Difference in boiling points
Difference in colour
Difference in density of solids
Difference in particle size
Tap an answer to check it.
WhyDistillation separates liquids that have different boiling points.
Ready to test yourself?
Practise Introduction to the particulate nature of matter with instant marking and per-topic score tracking.