CAUTION: Use appropriate safety guidelines in performing demostrations.

Demonstration 1: Types of Solutions

Purpose

To demonstrate types of solutions.

Safety

See individual demonstration cautions and use generally accepted procedures for safety as outlined in the safety section of the ChemSource materials.

Procedures

    Gas in gas: Gently warm I 2 crystals in a beaker over a water bath to observe I 2 vapor in the air. The beaker should be covered with a watch glass or evaporating dish. (CAUTION: Iodine vapors are corrosive to eyes, skin, respiratory tract, and other materials.)

    Gas in liquid: Deaerate well-aerated water by warming (bubbles of air should be apparent) or uncap soda pop bottle previously shaken lightly (CO ₂ will be evolved).

    Gas in solid: Previously freeze well-aereated water. In class, melt the ice and warm further to deaerate. (NOTE: Bubbles in the ice are not dissolved gases.)  Liquid in liquid: Mix ethanol with water. (CAUTION: Ethanol dehydrates  the skin. Use with care. No flames should be present. Avoid breathing solvent vapors.) The sum of the two volumes is not the same as the volume of the solution and can be shown by careful volume measurement. (100 mL ethanol + 100 mL water » 190 mL solution. The solute fills in the void volume (holes) of the solvent.)  Liquid in solid: The substance in a disposable diaper can dissolve water. The powder can be removed by cutting the diaper into 10 cm 2 pieces. Place the pieces in a plastic bag, close the bag, and shake out the powder. Sprinkle about one-halfÊteaspoon of the powder onto one-half cup water. Observe. (A gel-like solid should form.) Practice this since the amount of water that can be absorbed may vary with the brand of diaper. (This demonstration is adapted from the Polymer module. See demonstration 3 in the Polymer module for another example of this type of solution.) Solids in liquids (best known): Examples include solutions of sugar or salt (NaCl) in water. Anhydrous CuSO ₄ (white) dissolved in water (colorless) gives a blue solution. I ₂ in different solvents gives different colors (violet in cyclohexane, yellow in ethyl acetate, brown in water).

    Solids in solids: Using a soldering iron compare the ease of melting of a typical Sn-Pb alloy (solder) vs. Sn metal and/or Pb metal. (CAUTION: Beware of metal vapors from the solders. Alternatively, compare the properties of brass [Cu-Zn alloy] vs. the metallic elements Cu and Zn.)

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