Dissolving (rates of dissolving) - E

Name:
Do you remember what the meaning of DISSOLVING is? Write the definition here:
The RATE OF DISSOLVING tells us about how quickly a solute can dissolve in a solvent.
There are certain factors that can speed up the time it takes to dissolve a solute. They are
Temperature, agitation (stirring) and particle size.
Try these experiments which test how these factors affect the rate at which a solute dissolves.
Experiment 1:
AIM: Find out how temperature affects the rate of dissolving.
APPARATUS: 3 beakers, 100ml of hot water, tap water and ice-cold water, sugar, stopwatch.
METHOD: Add the 3 types of water to the 3 beakers. Put 1 teaspoon of sugar into the hot water and start the stop watch. Stir for 3 seconds and then stop. Stop the stopwatch when all the sugar is dissolved. Repeat these steps with the tap water and the ice-cold water. Record your results.
Temperature
Time to dissolve (s)
Hot
Temperature
Rate of
dissolving
Tap
Ice-cold
At which temperature did the sugar dissolve the fastest?
_________________________________________________________________________________
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Grade 6 Natural Science Term 2: Matter and materials; Dissolving; rates of dissolving
GRADE 6
Dissolving (rates of dissolving)
GRADE 6
AIM: Find out how agitation (stirring) affects rate of dissolving.
APPARATUS: 2 beakers, 200ml of tap water, sugar, spoon, stopwatch.
METHOD: Add 100ml of water to each beaker. Put 1 teaspoon of sugar into a beaker and start the stopwatch. Stir, and time, until all of the sugar is dissolved. Now repeat with the second beaker, but do not stir it. Record your results.
Agitation
Time to dissolve (s)
Stirred
Agitation
Rate of
dissolving
Not stirred
Did the sugar dissolve faster when stirred or not stirred?
___________________________________________________________________________________
Experiment 3:
AIM: Find out how particle size affects rate of dissolving.
APPARATUS: 2 beakers, 200ml of tap water, sugar grains, sugar cube, spoon, stopwatch.
METHOD: Add 100ml of water to each beaker. Put 1 teaspoon of sugar grain into a beaker. Stir whilst timing how long it takes for the sugar to dissolve. Repeat with the second beaker, putting in one large sugar cube. Record your results.
Particle size
Time to dissolve (s)
Fine sugar grains
Sugar cube
Grain size
(finer grains)
Rate of
dissolving
Which type of sugar dissolved the fastest?
___________________________________________________________________________________
© e-classroom 2015
www.e-classroom.co.za
Grade 6 Natural Science Term 2: Matter and materials; Dissolving; rates of dissolving
Experiment 2:
2) When you increase the agitation of the solvent, the solute dissolves faster. The more you stir the solvent, the faster the solute dissolves in it. If you don’t stir the solvent, the solute dissolves very slowly.
3) When you decrease the particle size of the solute, it dissolves faster. If the solute is made of fine grains, it will dissolve faster than if the solute is a solid block.
Watch the video about factors that affect the
rates of dissolving
https://www.youtube.com/watch?v=Sv3kU_xYOK0
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www.e-classroom.co.za
GRADE 6
1) When you increase the temperature of the solvent, the solute dissolves faster. The warmer the solvent, the faster it dissolves. The colder the solvent, the slower it dissolves.
Grade 6 Natural Science Term 2: Matter-and materials; Dissolving; rates of dissolving
Here are some CONCLUSIONS we can draw from these experiments:
Do you remember what DISSOLVING is? Write a definition here:
When a solute mixes with a solvent and the solute particles become joined to
the solvent forming a solution.
Experiment 1:
Temperature
Time to dissolve (s)
Hot
Tap
Ice-cold
(Answers will vary, but Hot should dissolve the quickest, tap water will dissolve more
slowly and ice-cold water will dissolve the slowest.)
At which temperature did the sugar dissolve the fastest?
The hot water
Experiment 2:
Agitation
Time to dissolve (s)
Stirred
Not stirred
(Answers will vary, but the time for the beaker that is stirred will be less than the time for
the “Not stirred” beaker.)
Did the sugar dissolve faster when stirred or not stirred?
When stirred
© e-classroom 2015
www.e-classroom.co.za
Grade 6 Natural Sscience Term 2: Matter and materials; Dissolving; rates of dissolving
GRADE 6
Memorandum
Particle size
Time to dissolve (s)
Fine sugar grains
Sugar cube
(Answers will vary, but the dissolving time for the beaker with the sugar grains will be
less than the dissolving time for the beaker with the sugar cube.)
Which type of sugar dissolved the fastest?
Sugar grains
The suger cube is more dense than the sugar grains and thus will take more time
for the water to penetrate and break it down. The sugar grains are smaller and
less dense which means they will dissolve quicker.
Particles that are smaller will dissolve quicker.
Grade 6 Natrural Science Term 2: Matter and materials; Dissolving; rates of dissolving GRADE 6
Experiment 3: