The Properties of Water

Property: Polarity

Activity #1 Surface Tension: PILE IT ON.

Materials: 1 DRY penny, 1 eye dropper, water.

Procedure: Make sure the penny is dry. Begin by estimating the number of drops of water that can be piled on the penny before it spills over. Gently place drops of water on the penny until the water spills over. Record the results.

ESTIMATE:ACTUAL AMOUNT:.

What property of water allows the water droplets to pile up on the penny?

2. Define the following:
Cohesion –

Adhesion-

Surface tension-

Activity #2 Surface Tension: THE “FLOATING” PAPER CLIP

Materials: paper clip, container with water, ice.

Procedure: Using a steady hand, see if you can get the paper clip to rest on the surface of the water in such a way that it will not sink. After you succeed, place a piece of ice in the water and answer the questions on your answer sheet.

3. What does it mean to “float”?

4. Is the paper clip actually floating? Explain.

5. What property of water allows a paper clip to rest on its surface?

Activity #3: Water as a Solvent

Because of its high polarity, water is called the universal solvent. A solvent is a substance that dissolves, or breaks apart, another substance (known as a solute). A general rule that determines whether a substance will dissolve in a solvent depends upon its polarity. Polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes.

In this activity, you will compare the ability of water, alcohol, and vegetable oil to dissolve certain solids. CAUTION: Rubbing alcohol is flammable, an eye irritant, and has fumes.

Materials: graduated cylinder, 40 ml of alcohol, 3 beakers, 9 test tubes, test-tube rack, 40 ml of water, 40 ml of vegetable oil, sugar, salt, and margarine.

Procedure:

  1. Number your test tubes (TT) 1-9.
  2. Pour 10 ml of water into TT marked 1-3.
  3. Pour 10 ml of alcohol into TT marked 4-6.
  4. Pour 10 ml of vegetable oil into TT marked 7-9.
  5. Place a cap full of sugar in TT 1, 4, & 7.
  6. Place a cap full of salt in 2, 5, & 8.
  7. Place a small piece of margarine in TT 3, 6, & 9.
  8. Cover each TT with your thumb and shake. How well does each solvent dissolve the solute?
  9. Observe and record the results.

Wash the TT with soap & water and reorganize the station so that it is ready for the next class.

Substance / Water / Alcohol / Vegetable Oil / Key
Sugar / +++ dissolves ~100%
Salt / ++ or + partial dissolve
Margarine / 0 did not dissolve

Table 1: Polar and Non-polar Solvents and Solutes

6. Which solvent dissolved the best?

7. What gives water the ability to dissolve things?

8. What general rule determines whether a solute will dissolve in a solvent?

9. From this experiment would you conclude that sugar is polar or non-polar? Explain.

Property: High Specific Heat and Heat of Vaporization

Activity #4: Comparing Water to Alcohol

Materials: 2 100 ml beakers, 2 thermometers, alcohol, water, stop watch, hot plate, goggles.

Procedure: READ ALL INSTRUCTIONS BEFORE STARTING!

  1. In one beaker measure out 30 ml of alcohol and in the other measure out 30 ml of water.
  2. Record the temperature of both the alcohol and the water.
  3. Place both beakers on a hot plate at the same time and heat them for 1 minute.
  4. Remove both beakers from the hot plate at the same time and record their temperatures.
  5. Allow the beakers to cool for around 2 minutes and record their temperatures again.
  6. Dump out the old water and alcohol and measure out 20 ml of alcohol and 20 ml of water.
  7. Place both beakers on the hot plate simultaneously and time how long it takes each liquid to boil.

8. Measure the temperature of the boiling liquids and record them on Table 2.

Before Hot Plate / After 1 minute / After cooling 2 min. / Time to Boil / Boiling point
Temp. of WATER (°C)
Temp. ALCOHOL (°C)

Table 2: Difference between Alcohol and Water

10. Which liquid changed temperatures the fastest and why?

11. Which liquid took longest to boil and why?

12. How does the high specific heat of water affect ecosystems?

Property: pH of Solutions and buffers

Activity #5: the pH of Common Substances

In this experiment, we will measure the pH of some common substances. We will do this with the pH meter.

In the following table, make your prediction of whether or not you think the substance is an acid or a base. Using the pH meter determine the pH of each of the substances and then based upon your measurements classify them as either an acid or a base.

Sample / Prediction
Acid or Base / pH
(pH meter) / Acid or Base
1
2
3
4
5
6
7
8
9
10

Table 3: pH of Common Substances

13. Are your predictions supported by your experimental data?

14. Of the substances tested, which was the most acidic? Which was the most basic?

15. Which solution produced the most ions? How do you know?

Activity #6: Buffering Action of Alka-Seltzer and Sea Water

Buffers are solutions or liquids whose chemical makeup neutralizes acids or bases without a great change in pH. In this experiment you will be looking at the buffering effect of two possible buffers, Alka-Seltzer which provides relief from acid indigestion, and sea water. The samples will be titrated with either a strong acid (HCl) or a strong Base (NaOH) and the pH measured.

Materials: 100 ml beaker,1 M HCl dropper bottles, 1 M NaOH dropper bottles, pH meter, 50 ml Alka-Seltzer Solution, 50 mlsea water, Glass stirring rod

Procedure:

  1. Fill the 100 ml beaker with 50 ml of tap water and record the pH.
  2. Add 3 drops of HCl to the beaker stir the solution with the glass rod and record the pH (Table 2).
  3. Add 3 more drops of HCl to the beaker, stir the solution with the glass rod and record the pH. Repeat step three two more times (total of 12 drops).
  4. Repeat steps 1-3 using 50 ml of the Alka-Seltzer solution
  5. Repeat steps 1-3 using 50 ml of the sea water.
  6. Graph your data with the drops of HCl on the horizontal axis and pH on the vertical.
  7. Fill the 100 ml beaker with 50 ml of tap water and record the pH.
  8. Add 3 drops of NaOH to the beaker, stir the solution with the glass rod and record the pH (Table 3).
  9. Add 3 more drops of NaOH to the beaker, stir the solution with the glass rod and record the pH. Repeat step three two more times (total of 12 drops).
  10. Repeat steps 7 and 8 using 50 ml of the Alka-Seltzer solution
  11. Repeat steps 7 and 8 using 50 ml of the sea water.
  12. Graph your data with the drops of NaOH on the horizontal axis and pH on the vertical.

Sample / Initial pH / pH (3 Drops HCl) / pH (6 Drops HCl) / pH (9 Drops HCl) / pH (12 Drops HCl)
Tap Water
Alka-Seltzer
Sea Water

Table 4: pH of Samples Titrated with HCl

Sample / Initial pH / pH (3 Drops NaOH) / pH (6 Drops NaOH) / pH (9 Drops NaOH) / pH (12 Drops NaOH)
Tap Water
Alka-Seltzer
Sea Water

Table 5: pH of Samples Titrated with NaOH

  1. Describe any changes that took place in the solutions?
  1. Explain why these changes occurred.
  1. Did the Alka-Seltzer and the liver extract solutions react the same way? Explain?
  1. Based on this experiment, what does it mean when a solution is buffered?