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Matter Lab 6-8 / Week 05 / Bench Day
6/6
Week 05 · Mixtures and Solutions

Bench Day

Bench Day: Mix it, then unmix it
// Together, but still themselves
⏱ about 20 min

Bench Day: Mix It, Then Unmix It

Saturday morning, Rocket pours salt, sand from the plant pot and water into one jar. He shakes it hard.

"A total mess," he says proudly. "Now we take it apart."

Raven sets a coffee filter in a funnel over a clean cup. "What do you notice as it drips through?"

The water comes out clear. The sand stays behind in the filter, dark and wet.

"Now the salt," Rocket says. He pours the clear water into a shallow dish and sets it in the sun.

Nova hovers by the window. "Patience is a lab tool too," she says. "Check it tomorrow."

Raven writes in the Bench Log: "Filter for the sand. Sun for the salt. Everything kept its properties."

  1. A mixture is two or more substances in any proportion. The substances keep their own properties.
  2. A homogeneous mixture is the same throughout. A heterogeneous mixture varies from place to place.
  3. A solution is a solute dissolved in a solvent, with particles too small to see, settle or filter out.
  4. A saturated solution holds the maximum solute that can dissolve. For table salt, that is 36.0 grams per 100 grams of water at 20 degrees Celsius.
  5. Mixtures are separated by using properties the parts kept: filtering by particle size, evaporating by letting the liquid leave.
◇ FAMILY MIX AND UNMIX
Together, stir one spoonful of salt and one spoonful of sand or dry soil into a jar of water.
Pour the mixture through a coffee filter into a clean cup. Take turns holding the funnel and pouring.
Pour the filtered water into a shallow dish. Set it in a sunny, safe spot where it will not be knocked over.
Check the dish each day. When the water is gone, look closely at what is left and talk about where it came from.
For a grown-up
Only tap water is used, and nothing is tasted. Soil or sand from outdoors is handled with washed hands afterward.
The evaporating dish may take several days. A warm windowsill speeds it up. No heat source is used.
The separation methods this week come from a chemistry text hosted by the University of California, Davis. The salinity data come from the U.S. Geological Survey, at usgs.gov.
Safety first
Nothing goes in your mouth. Nothing is tasted.
Wash your hands after handling soil or sand.
Wipe up spills so the floor stays dry.
THINK IT THROUGH
  • Read the question.
  • Tap your answer.
The sand stayed in the filter but the salt went through. Why?
What will be left in the dish when the water is gone?
Bench Day checkTrue or false?
Filtering separates sand from water because sand particles are large.?
Evaporation makes the salt disappear forever.?
The salt in the jar kept its properties the whole time.?
WHY THIS EXERCISETaking a mixture apart proves the parts never stopped being themselves.
Draw the three stages: the shaken jar, the filter with sand in it, and the dish with the water gone.
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