Which solid can be mixed with solid

Mixtures and Solutions

Authors: Anonymous
Publication: 1.1.1998
Learning level: 3
Overview: On the basis of simple experiments, the students discover the properties of different liquids. You will acquire basic knowledge about dissolving substances in liquids.
Duration: 4 lessons (some in group work)
Material: For 30 students:
  • 30 glasses
  • 60 plastic spoons
  • 6 table scales
  • 30 identical transparent vessels
  • Any 24 clear vials
  • 12 test tubes
  • 6 droppers or syringes (straws are difficult to use)
  • 6 bowls (or the bottom half of plastic bottles)
  • 6 sponges
  • 1 kitchen roll
  • 4 plates
  • 1 saucepan
  • 1 package of filter bags
  • 1 heating plate
  • Salt, rice, powdered sugar, lump sugar, sand, syrup, oil, vinegar, instant coffee, water
Origin: La main à la pâte, Paris
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Terms

  • Solubility: soluble or insoluble solid.
  • The mass of a substance is retained even after it has been dissolved.
  • Miscibility: mixable or immiscible liquids.
  • Constant sequence when "superimposing" liquids.
  • Volume mass: The same volumes of different liquids have different masses.

Desired skills

  • Being able to ask questions to others and yourself.
  • Being able to describe an attempt.
  • Being able to communicate your own approach.
  • Isolate a variable and conduct meaningful experiments.
  • Recognize the need for measurements.
  • Being able to present the test results in writing (texts, schematic illustrations, ...).

1st lesson: soluble or insoluble?

initial situation

We cooked on a school trip. We mixed solids and liquids.

Question

Are all solids soluble in water?

Student hypotheses

Some solids "disappear" in the water, others don't.

Experiments suggested by the students

Mix various solids with water.

Attempt carried out in class

For the experiment, glasses, spoons and various solid substances are required: salt, rice, powdered sugar, sugar cubes, flour, soluble coffee.

  • Mix the different substances with water.
  • Observe factors that affect the speed of dissolution:
    • shake
    • temperature
    • Amount of solid in relation to water
  • Note and draw observations.
  • Collect observations from the various groups.
  • Correct used vocabulary: "melting" is often used incorrectly; Introduction of the words soluble, (dissolve), insoluble, clear mixture.

 

 

Fig. 1-3: Excerpts from test booklets

Teacher's comment

The so-called "soluble" coffee is actually a suspension, which is difficult to convey to children (the liquid is black).

literature

  • Explore and experience water. A water workshop for grade 3/4, Wilfried Stascheit, Verlag An der Ruhr, 2006
  • How so? Why? Why ?: Experiment and discover. More than 30 experiments on air and water, Angela Weinhold, Ravensburger, 2004
  • Special issue water. For the 3rd and 4th grade. (Learning materials), Alice Undorf and Daniela Prosch, Bvk Buch Verlag Kempen, 2003
  • Water explorers and air kisses. Help, tips and suggestions for curious children, Andrea Hündlings, Verlag An der Ruhr, 2007
  • Water workshop. Exciting experiments around ice and water. Ulrike Berger, Oz Verlag, 2004

2nd lesson: can a dissolved solid be recovered?

Questions

  • Is the solid still there in a solution?
  • How can you recover a dissolved solid?

Student hypotheses

You can't see the solid, but it's there.

Experiments suggested by the students

  • Try the solution.
  • Weigh the solid and water; then weigh the mixture.
  • Filter the mixtures.
  • Let the water evaporate (in the air or by boiling it).

Experiments carried out in class

The following materials are needed for these experiments: salt, water, scales, glasses, filters, pots and a heating plate.

Attempt 1

  • Try the solution (with the teacher's consent).

Attempt 2

  • Weigh the salt, weigh the water.
  • Check that the mass of the saline solution equals the sum of the masses of the water and the salt.
  • Compare the results.

Finding

The mass of salt water is equal to the sum of the masses of water and salt used to make the salt solution. "The salt not only gives the solution its taste, it is completely in the solution."

Fig. 4: Extract from a test booklet

Attempt 3

  • Filter a water-sand suspension.
  • Filter a water-salt solution.

Finding

You can reclaim the sand, but not the salt. Filtering can be used to separate the components of a mixture if the solids are insoluble.

Fig. 5: Has the salt disappeared?

Attempt 4

Let the water evaporate, on the one hand in the air and on the other hand by boiling.

Finding

Salt crystals appear. The solids dissolved in water can be recovered by evaporation or evaporation of the water.

Fig. 6: How can the salt be recovered?

Teacher's comment

The following procedure is recommended for weighing water, salt and salt water: Instead of weighing water, salt and salt water individually, you can place the water and salt side by side on the same weighing pan. Then you tare the scales with a weight. Then you dissolve the salt in the water and put the vessel back on the scales. This avoids having to make sums while weighing.

additions

  • Investigation of salt pans.
  • Obtain fresh water from salt water.

literature

  • The way of the white gold. A cultural history of salt, Frederic Denhez, RvR, 2006
  • The salt workshop (learning materials). Diana Dudde, Verlag An der Ruhr, 2005

3. Lesson: What happens if one liquid comes into contact with another liquid?

initial situation

  • Make a vinaigrette (salad dressing with vinegar and oil).
  • Make a mixture of syrup and water.

Question

What happens if you pour the following liquids into the same container:

  • Water and syrup,
  • Oil and vinegar?

Student hypotheses

  • The water and syrup mix (when you shake).
  • You can see: vinegar "bubbles" on the oil; Oil "bubbles" on the vinegar.

Attempt suggested by the students

We mix two of these liquids.

Attempt carried out in class

The following materials are required for this experiment: transparent vessels, spoons, water, syrup, oil and vinegar.

  • You make the mixes, paying careful attention to:
    • the order in which the liquids are poured into the jar,
    • the observations before shaking,
    • the observations after shaking.
  • Joint discussion of the results and repetition of the experiments if the observations in the different groups differ from one another.
    For example, if you pour the syrup first and then the water, you get a mixture straight away.
    But if you first pour the water and then the syrup into the glass, the syrup remains on the bottom and you have to shake or stir so that the liquids mix.
  • Summary of the results (in the form of a table).

Fig. 7: What happens if you mix water and syrup or oil and vinegar?

Findings

  • If you shake the mixture of water and syrup, you get a clear mixture. It is said that the liquids are miscible with one another.
  • If you shake the mixture of oil and vinegar, the two liquids become a cloudy mixture (emulsion).
  • If you let the oil and vinegar mixture stand, the liquids separate; they cannot be mixed with one another.

Teacher's comment

Students often suggest mixtures with milk. You then have to explain to them that milk is already an emulsion.

4th lesson: Why do some liquids always settle on the floor?

initial situation

  • The oil always floats above the vinegar.
  • If you don't shake the syrup is always under the water. Is that correct?

Question

  • Can you change the order in which liquids are stacked on top of each other?
  • Why should the order always be the same?

Student hypotheses

  • The order can possibly be changed.
  • The darkest, the thickest, the heaviest liquid always goes down.

Experiments suggested by the students

  • Try the following:
    • "Deposit" syrup drops on the water surface,
    • likewise vinegar drops on the oil.
  • The quantities change: a lot of one, little of the other.
  • Pour the liquids into the glass in a different order.
  • Observe the liquids at the bottom of the glass (dark, thick ...)
  • Weigh the liquids; which one is heavier?

Experiments carried out in class

The following material is required: 6 scales (1 per group), 24 identical transparent vessels, 12 test tubes, 6 small bowls (lower halves of plastic bottles), 4 small bottles per group, 6 drop counters (straws, syringes), syrup, vinegar, oil, 6 sponges and kitchen roll

Attempt 1

The drop counter is used to add various liquids to the water.

Finding

  • The syrup can mix with water, but it never rises.
  • The vinegar drops sink through the oil layer.
  • The same liquid always remains on the floor.

If the criterion "fat" is mentioned: Only one of these four liquids is fat, so one cannot deduce from this that fat always floats on top.

Attempt 2

  • Observe the liquids at the bottom of the glass.
  • Check the criteria "dark" and "thick".

Finding

For the syrup:

  • Criterion "dark": yes
  • Criterion "thick": yes

For the oil:

  • Criterion "dark": no
  • Criterion "thick": no

conclusion

These criteria are not suitable.

Attempt 3

  • Weighing
  • The students should think of experimental arrangements (= identical vessels and liquid levels).
  • Some groups deal with water and syrup, the others with oil and vinegar.
  • In some cases, known weights are used.
  • Sometimes two vessels with different liquids - but the same liquid volumes - are placed on the two weighing pans.

Finding

When two liquids overlap, the lighter one (with the same volume) is on top.

complement

  • Let's try layering other liquids on top of each other.
  • Let's try to stack more than two liquids in the same vessel.

Last update: April 15, 2015

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