Demonstration of Polarity - Chemistry

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Demonstration of Polarity - Chemistry

By | April 2011
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Baron Hasslinger

Chemistry

Like Dissolves Like — a Demonstration of Polarity
Aim: To illustrate that polar solutes dissolve in polar solvents and that non-polar solutes dissolve in non-polar solvents by mixing polar and non-polar solutions in test tubes. Material: • Lab coats and safety spectacles • A fume cupboard • Heptane • Water • Potassium Permanganate • Iodine • 2 test tubes • 4 small flasks Method: (Wear safety specs and lab coats) • Prepare 4 small flasks containing: • A Heptane • B A weak solution of potassium permanganate, made by putting a few crystals of KMnO4 in 100 ml of water. Dilute this with more water until it is the same colour as D • C Water • D Iodine in heptane. Dissolve a few crystals of iodine in heptane until the colour in the same as in B Then (in a fume cupboard): • 1. Mix a little of A and B together in a test tube. Describe what you see. • 2. Mix a little of C and D together in a test tube. Describe what you see. • 3. Add a little water to the mixture of C and D. What happens? • 4. Add a little water to the mixture of A and B. What happens? • 5. Add a little heptane to the two mixtures. What happens? Results: Nr. 1 Observations The substances do not mix but separate neatly with one on top (A) and one on the bottom (B). A meniscus that is concave up forms between the substances. The substances do not mix but separate neatly with one one top (D) and one on the bottom (C). A meniscus that is concave up forms between the substances. The water sinks down through the heptane into the water at the bottom and dissolves in it. Explanation The substances wonʻt mix as one is polar and the other one non-polar. A stays on top as heptane is lighter than water. The meniscus forms because of the adhesive properties of water. The substances wonʻt mix as one is polar and the other one non-polar. D stays on top as heptane is lighter than water. The meniscus forms because of the adhesive properties of water. As the water is denser than the heptane,...
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