7th grade · Science · Unit 9 of 10
Mixtures & Solutions
Mix it, dissolve it, separate it
What your child practices
Telling pure substances from mixtures, mechanical mixtures from solutions, solutes and solvents, comparing concentration, and choosing separation methods like filtering, evaporation, magnets and distillation.
Alaska content standards learning standard: MS-PS1-2 · properties such as solubility that tell pure substances and mixtures apart
How we explain it
Children can open this short lesson before they practice.
- A pure substance has one kind of particle. A mixture has more than one.
- In a mechanical mixture you can see the parts. In a solution, the solute dissolves in the solvent.
- Separate by filtering, evaporating, using a magnet or distilling.
Example: Cup A has 10 g of sugar in 100 mL of water. Cup B has 20 g in 100 mL. Which is more concentrated? Both have the same amount of water. Cup B has more sugar in it. Answer: Cup B
Mixtures & Solutions in Alaska
In the Alaska content standards, this is unit 9 of 10 in 7th grade Science, after Earth's Moving Surface and before Particles and Heat.
Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.
Source: Alaska Department of Education and Early Development
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
Which method separates small pebbles from fine sand?
- evaporation
- boiling
- using a magnet
- sifting through a sieve
sifting through a sieve
Hint: A sieve (screen) has holes that let small grains fall through and keep the bigger pieces.
Question 2
Steel is mostly iron with a little carbon spread evenly through it. What kind of matter is steel?
- a gas
- a pure element
- a mixture (a solid solution)
- a suspension
a mixture (a solid solution)
Hint: Steel is made of more than one substance, mixed evenly. Metal mixtures like this are called alloys.
Question 3
In fizzy water (carbon dioxide gas dissolved in water), which is a solute?
🧪- carbon dioxide gas
- water
- fizzy water
carbon dioxide gas
Hint: The solute is what dissolves (usually the smaller amount). The solvent does the dissolving (usually the larger amount). Together they make the solution.
Question 4
What is a pure substance?
- matter made of only one kind of particle
- anything found in nature
- two substances stirred together
- any liquid you can see through
matter made of only one kind of particle
Hint: Distilled water, table salt and gold are pure substances. Each is made of just one kind of particle.
Question 5
How could you separate sand from water?
🏖️- use a magnet
- pour it through a filter
- stir it faster
- add more water
pour it through a filter
Hint: A filter lets water pass through but traps the bigger sand grains.
Question 6
What can Priya conclude from her experiment?
Seconds for a sugar cube to dissolve - Sugar dissolves faster in colder water
- Water temperature makes no difference
- Sugar dissolves faster in warmer water
- Sugar can't dissolve in hot water
Sugar dissolves faster in warmer water
Hint: Look at how the bars change as the water gets warmer. A shorter bar means less time to dissolve.