8th grade · Science · Unit 1 of 16
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.
Alabama Course of Study content standard: 8.1; 8.3 · pure substances, mixtures and solutions, and solubility
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 Alabama
In the Alabama Course of Study, this is unit 1 of 16 in 8th grade Science, before Density & Buoyancy.
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.
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 cup of sugar water is the least concentrated?
Sugar water cups Cup Sugar Water A 5 g 100 mL B 2 g 100 mL C 10 g 100 mL D 8 g 100 mL - Cup B
- Cup D
- Cup C
- Cup A
Cup B
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 2
Mechanical mixture or solution? Tap an item, then tap its basket.
Sort into: 🥣 mechanical mixture · 🧪 solution
- 🍕pizza
- 🥗salad
- 🍵sugar dissolved in tea
- 🎺brass (copper and zinc)
- 🥤fizzy water
- 🍪chocolate chip cookie
🥣 mechanical mixture: pizza, salad, chocolate chip cookie · 🧪 solution: sugar dissolved in tea, brass (copper and zinc), fizzy water
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 3
In salt water, which is the solvent?
🧪- salt
- water
- salt water
water
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
How can you get pure drinking water from salt water?
- distillation: boil it and collect the cooled steam
- stir in more salt
- pour it through a paper filter
- use a strong magnet
distillation: boil it and collect the cooled steam
Hint: When salt water boils, only the water turns to steam. Cooling the steam turns it back into pure water.
Question 5
Which of these is a solution?
- a bowl of cereal and milk
- sugar dissolved in water
- a tossed salad
- sand and gravel
sugar dissolved in water
Hint: In a solution, one substance dissolves into another and looks the same throughout.
Question 6
Panning for gold works because gold is…
🪙- dissolved in the river water
- lighter than sand, so it floats
- magnetic, so it sticks to the pan
- denser than sand, so it sinks to the bottom of the pan
denser than sand, so it sinks to the bottom of the pan
Hint: Swirling the pan washes the lighter sand away while the heavy gold settles.