Investigating the Rate of Dissolving
Understanding the factors that affect how quickly a substance dissolves is important to the
manufacturing of medicines, dyes, and processed foods. For example, some cold relief remedies are powders
that must be mixed with hot water. Scientists do tests to ensure that the powder dissolves quickly in hot water.
In addition, when you add sugar to a drink, several factors affect how quickly the sugar dissolves. Today, we
will be investigating ways to speed up how fast sugar dissolves in water.
** The rate of dissolving is a measure of how fast solute dissolves in a solvent (eg. in seconds).
Purpose: To investigate how the rate of dissolving is affected by the size of the solute, the rate of stirring,
and the temperature of the solvent.
Materials:
- hot, cold, and room temperature water
- sugar cubes
- granulated sugar
- stirring spoons
- beaker
- watch or clock
Procedure:
PART A: SIZE OF THE SOLUTE PARTICLE.
a) Pour 100mL of room temperature water into a beaker.
b) Get 1 sugar cube and bring it back to your desk with the beaker and a stirring spoon.
c) Add the sugar cube to the beaker and start timing.
d) Stir at a normal/moderate rate until the sugar cube is completely dissolved.
e) Record the time it took to dissolve in the observation chart on the back of this page.
f) Repeat the above steps except this time use 1 scoop of granulated sugar.
PART B: RATE OF STIRRING.
a) Pour 100mL of room temperature water into a beaker.
b) Get 1 scoop of granulated sugar and add it to the beaker and start timing.
d) Stir at a slow rate until the sugar is completely dissolved.
e) Record the time it took to dissolve in the observation chart on the back of this page.
f) Repeat the above steps except this time stir at a fast rate.
PART C: TEMPERATURE OF THE SOLVENT.
a) Pour 100mL of cold water into a beaker.
b) Get 1 scoop of sugar and add it to the beaker and start timing.
d) Stir at a normal/moderate rate until the sugar is completely dissolved.
e) Record the time it took to dissolve in the observation chart on the back of this page.
f) Repeat the above steps except this time use hot water.
Observations:
Time Required For Sugar to Dissolve (Seconds)
Solute Size
Stirring Rate
PART A
Whole Cube
Small Pieces
Temperature
PART B
Slow
PART C
Fast
Cold
Hot
Conclusions:
Write a conclusion for each part (a, b, and c) and make sure to relate each answer back to the original purpose
of the experiment.
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B)________________________________________________________________________________________
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C)________________________________________________________________________________________
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Application Question:
THE PARTICLE THEORY AND RATE OF DISSOLVING
Particles on the outer edge of a piece of solute are attacked and carried away by solvent particles. Even
when there is no stirring, the particles are always moving. Stirring moves water particles next to the sugar
crystal. The water has a lower concentration of sugar, so the water particles can attract more sugar.
For the effect of temperature on the rate of dissolving, did you recall the fifth point in the particle
theory? The fifth point states that particles at a higher temperature are moving more quickly. So, again, the
sugar-saturated water particles move away from the sugar, allowing pure water particles to take their place near
the sugar.
You have seen that when a solid solute is dissolving in a solvent, the dissolving occurs on the surface of
the piece of solute. When the solute is in smaller pieces, there is more surface area where dissolving can occur.
1. Use the particle theory to explain the three conclusions that you made above.
A)_______________________________________________________________________________________
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B)________________________________________________________________________________________
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C)________________________________________________________________________________________
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