Science 6th grade | UNIT 3: Material changes 3.6 How can we make solids dissolve faster?
Why do you think the coffee tasted bitter? How could the boy make the coffee taste sweeter without adding any more sugar?
The coffee and sugar form a solution. The sugar will dissolve faster if the boy stirs the solution. Stirring is one way to make solid solutes dissolve faster.
Stirring causes the particles of the solute to spread out into the spaces between the particles of the solvent more quickly. We say that stirring increases the rate at which a solute dissolves.
There are other factors that make solids dissolve faster. Have you ever tried to make coffee with water from the fridge? Why do we use hot water?
Activity 3.6 (Does sugar dissolve more quickly in hot or cold water?)
You will need: sugar - glass jars - cold water - hot water - teaspoon - measuring cylinder stopwatch
Does sugar dissolve more quickly in hot or cold water? Make a prediction.
Stir a teaspoon of sugar into 100 ml of cold water in a glass jar.
Stir a teaspoon of sugar into 100 ml of hot water in a glass jar.
Time how long it takes for the sugar to dissolve in both jars.
Record your results in a table.
Questions
1) a: In which jar did the sugar dissolve quickest? Suggest a reason for this.
b: Was your prediction correct?
2) How did you make sure that your test was fair?
3) Write down what you conclude about the effect of temperature on dissolving a solute.
The particles in matter are always moving. When we increase the temperature of a substance, the heat adds energy to the particles of the substance. This energy causes them to move faster.
In a heated solvent, the particles of the solute move faster than in a cooler solvent. This allows the particles of the solute to spread through the solution more easily, so the solute dissolves faster.