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Matter Lab 6-8 / Week 05 / Wednesday
3/6
Week 05 · Mixtures and Solutions

Wednesday

Bench Lab: Three cups, three mixtures
// Together, but still themselves
⏱ about 20 min

Wednesday: Bench Lab: Three Cups, Three Mixtures

Three clear cups of water wait on the Bench. Beside them sit salt, cornstarch and cooking oil.

"One spoon of each, then stir," Rocket says. "Then we watch."

Raven sets a timer. "Predict first. Which one becomes a solution?"

"Salt," Rocket says. "The cornstarch might. The oil will not."

Nova hovers over the cornstarch cup. The water has turned milky white. "Give it time," she says. "Settling takes a while."

Ten minutes later, Raven taps the cup. "What do you notice at the bottom?" A soft white layer has gathered there.

"So the cornstarch did not really dissolve," Rocket says. "It just hid for a while." Nova hums. "Now measure the salt."

Your mission

Today you make three mixtures and sort each one as a solution, a suspension or a two-layer heterogeneous mixture.

Then you find out how many spoonfuls of salt a cup of water can hold before it is saturated.

  • Four clear cups and a spoon for each
  • Water, salt, cornstarch and cooking oil
  • A measuring cup and a measuring teaspoon
  • A coffee filter or paper towel and a fifth empty cup
  • A timer or clock, and your Bench Log
Safety first
Use only cool or warm tap water. Nothing is heated.
Nothing goes in your mouth, and nothing is tasted. Keep your hands away from your face.
Wear safety glasses or sunglasses while stirring and pouring.
Wash your hands when you finish. Leftovers go down the sink with running water.
  1. Measure one cup of water into each of three cups. Label them salt, cornstarch and oil with tape.
  2. Add one teaspoon of salt to the first cup and stir for one minute. Record what you see.
  3. Add one teaspoon of cornstarch to the second cup and stir for one minute. Record what you see.
  4. Add one teaspoon of cooking oil to the third cup and stir for one minute. Record what you see.
  5. Set a timer for ten minutes. Then look at each cup again, especially the bottom, and record any change.
  6. Pour the cornstarch cup slowly through a coffee filter into the empty cup. Record what stays in the filter.
  7. Return to the salt cup. Add one teaspoon of salt at a time, stirring one minute after each. Count the spoonfuls.
  8. Stop when a spoonful will not dissolve after a full minute of stirring. Record the total number of spoonfuls.
PREDICT BEFORE YOU STIR
  • Read the question.
  • Tap your answer.
Salt and water are a solute and a solvent. Which kind of mixture will the salt cup become?
Oil and water do not mix evenly. What will you see in the oil cup?
If particles sink to the bottom after ten minutes, what kind of mixture was it?
CupRight after stirringAfter ten minutesFilter resultMy sort: solution, suspension or layers
Salt
Cornstarch
Oil
Salt testMy count
Spoonfuls that dissolved
First spoonful that would not dissolve

Reading the result

Solid material in a suspension settles out on standing and can be removed by filtration. A solution passes straight through the filter.

Your salt count is your own measurement of saturation. Chemists found 36.0 grams per 100 grams of water at 20 degrees Celsius.

A teaspoon of salt is not exactly a gram, and a cup of water is more than 100 grams. Your count is a kitchen version.

Stirring and breaking up the solute change how fast it dissolves. They do not change the total amount that can dissolve.

What the lab showsTrue or false?
A solution passes through a coffee filter unchanged.?
Stirring faster lets more salt dissolve in total.?
Solid material in a suspension can be removed by filtering.?
Oil dissolved in the water to make a solution.?
WHY THIS EXERCISEFiltering and settling are the tests that tell a suspension from a solution.
How many kinds of mixture did you make today? Type a number.
WHY THIS EXERCISEOne Bench, three cups, three kinds of mixture: that is the whole week in a row.
Sketch your three cups after ten minutes. Label each one solution, suspension or two layers.

Careful measuring. Tomorrow you will read real solubility data and see how temperature changes the limit.

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