7th grade · Science · Unit 2 of 12
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.
Oregon State Standards learning standard: 7.PS1.2 · properties such as solubility that tell pure substances and mixtures apart
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
Mechanical mixture or solution? Tap an item, then tap its basket.
Sort into: 🥣 mechanical mixture · 🧪 solution
- 🥜trail mix
- 🌬️air
- 🥗salad
- 🍕pizza
- 🧂salt dissolved in water
- 🎺brass (copper and zinc)
🥣 mechanical mixture: trail mix, salad, pizza · 🧪 solution: air, salt dissolved in water, brass (copper and zinc)
Hint: In a mechanical mixture you can see the different parts. In a solution, one substance dissolves into another, so it looks the same all the way through.
Question 2
What is a pure substance?
- any liquid you can see through
- two substances stirred together
- anything found in nature
- matter made of only one kind of particle
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 3
Salt stirred into water seems to disappear. What happened?
🧂- It was destroyed
- It turned into water
- It dissolved, forming a solution
- It melted into a liquid
It dissolved, forming a solution
Hint: The salt is still there (taste it!). Its particles spread out evenly among the water particles. That's dissolving, not melting.
Question 4
Why can't a magnet pick up aluminum cans?
- Aluminum isn't magnetic
- Aluminum is too heavy
- Magnets only attract plastic
- The cans are empty
Aluminum isn't magnetic
Hint: Only a few metals, like iron, nickel and cobalt, are attracted to magnets.
Question 5
Which cup of sugar water is the most concentrated?
Sugar water cups Cup Sugar Water A 24 g 200 mL B 16 g 200 mL C 10 g 100 mL D 6 g 200 mL - Cup A
- Cup B
- Cup D
- Cup C
Cup A
Hint: Concentration is how much solute is dissolved in an amount of solvent. Work out the grams of sugar in each 100 mL of water, then compare.
Question 6
Pouring off the liquid after solids have settled to the bottom is called…
- sifting
- distilling
- evaporating
- decanting
decanting
Hint: Think of carefully pouring water off the top of a jar of settled mud.