Answer to Question #182247 in General Chemistry for Homos

Question #182247


a. Put water in a glass up to its lid. Let it settle for a while on top of a table.

b. Get a teaspoon of starch and sprinkle it on a top of the water on a glass.

c. Observe the motion of the starch on the water. Record your observation as an answer to Hypothesis 1.

d. Get a glass of water and another glass with oil. Fill in equal amounts of water and oil.

e. Using 2 marbles, drop each marble on both liquids.

f. Observe the travel time of each marble on both liquids until it reaches the bottom. Record the time as your evidence of travel.

g. Use this data to answer Hypothesis 2.

Guide Questions:

1. What are the significant results in your drop test?

2. How will you explain this result scientifically?

3. Will your observation be used in describing viscosity as a property of liquid? How?

Expert's answer

1. Starch neither dissolves, nor sinks at the bottom of the glass when sprinkled on the water, but instead remains undisturbed, and suspended in water.

2. Using the kinetic theory of molecules, intermolecular forces of attraction between the starch molecules and water molecules are relatively low compared to the cohesive forces of attraction between the water molecules and starch molecules. There is therefore almost no interaction between the starch molecules and the water molecules.

3. From the observations, we can describe surface tension as the property of a given liquid. Surface tension acting perpendicularly per unit length across the surface of water makes it behave as if it is covered with a stretched elastic skin, hence the starch stays on it without sinking.

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