SURFACE AREA, TEMPERATURE AND DISSOLUTION RATE EXPERIMENT
Valley Alternative High School
Dr. Gilbert
CONCEPTS: Dissolution rate, surface area, solvent-solute interaction, temperature effects, solubility curves
MATERIALS: Sugar (cubes, granulated, powdered); Salt (cubes and granules); stop watch; Thermometer; beaker; hot plate; water
PRINCIPLES and PROCEDURES: In the middle of the night of March 24, 1989, the giant oil tanker Exxon Valdez veered out of the shipping lanes in Alaska’s Prince William Sound and struck a reef. The side of the tanker was ripped open and 11 million gallons of crude oil flowed into Alaska’s clear blue waters. Because petroleum oil is less dense, it quickly spread across the surface the way vegetable oil spreads on the surface of vinegar shortly after a vinaigrette salad dressing is shaken. The oil slick eventually covered 10,000 square miles, contaminating 1500 miles of shoreline, and causing substantial damage to wildlife, the fishing industry, and the marine environment.
PART A
You have several tasks to do in this experiment. How might particle size be related to dissolution? How might temperature be related to dissolution? Finally, do different chemicals dissolve at different rates?
Determine the mass of a single sugar cube, and then measure out equivalent masses of powdered and granulated sugar, and salt. Record the water temperature in your notebook. Place the three forms of sugar and the salt in four different flasks. Pour 50 ml of water in the flask containing the sugar cube, and swirl the flask slowly and constantly. Record the time at which no more sugar can be seen in the flask. Repeat the process using granulated and powdered sugar and the salt. Compare the dissolution times for all three forms of sugar and the salt. Which form of sugar dissolves the fastest? Why?
QUESTIONS:
Rank the three forms of sugar in order of the time required for complete dissolution.
The three forms of sugar had the same mass, but different surface areas. Which had the largest surface area, and which had the smallest?
What influence does surface area have on the rate of dissolution? Explain what occurs at a molecular level to produce this effect?
Do you think that large salt crystals will promote ìrapid saltinessî or ìsaltierî tasting water. Explain
Many recipes require that you stir while adding a solute (like sugar, powdered milk) to a solvent. Explain the influence of stirring on the dissolution rate
PART B
Repeat Part A; however, this time use hot water
QUESTIONS:
What is the influence of temperature on the solubilities of cubed, granulated and powdered sugar and salt?
Which substance is more soluble in water? Explain
Solubility may be expressed as the number of grams of solute that dissolve in a 100 ml of water. According to your data, what are the solubilities of sugar and salt at each temperature?
EXTRA CREDIT:
Which solution is it easier to float a needle on? Explain.
How many can you float?
If a ship fills its ballast holds with ocean water than travels into the Great Lakes (freshwater) will it be riding higher or lower in the water? Explain.