Chemistry 8 Lesson 40: Solutions
1. Theoretical Summary
1.1. Solvent – Solvent – Solution
a) Experiment 1: Dissolving sugar in water, we get a sugar water solution
Comment: Sugar crystals dissolve in water to form a transparent solution that cannot be distinguished from sugar or water.
+ Solute: Sugar
+ Solvent: Water
+ Solution: Sugar water
b) Experiment 2: Solubility of cooking oil and gasoline in water
– Some pictures illustrate the solubility of cooking oil and gasoline in water
– They pay attention to the observed phenomenon when adding cooking oil to water and in organic solvents such as gasoline, CCl4, …
Video 1: Compare the solubility of cooking oil in organic solvents
– Comment: Cooking oil is insoluble in water but soluble in organic solvents such as gasoline, CCl4,…
+ Solvent: A substance that can dissolve another substance to form a solution
+ Soluble: is a substance that is dissolved in a solvent
+ Solution is a homogeneous mixture of solvent and solute
1.2. Unsaturated solution. Saturated solution
– In the first stage: we get a sugar solution, this solution can still dissolve more sugar ⇒ Unsaturated solution
– In the later stage: keep dissolving sugar forever until it can’t be dissolved anymore The solution is saturated
Conclusion: At a specified temperature:
An unsaturated solution is a solution in which more solute can be dissolved
– A saturated solution is a solution that cannot dissolve more solute
1.3. How does the dissolution of solids in water happen faster?
a) Stir the solution
Stirring the solution creates new contact between the solid molecules and the water molecules Dissolution occurs faster
b) Heat the solution
At higher temperatures, the faster the molecules move, increasing the number of collisions between the water molecules and the solid surface ⇒ The dissolution takes place faster
c) Crushing solids
Crushing the solid increases the contact area between the solid and the water molecule The smaller the size of the solid, the faster the dissolution
2. Illustrated exercise
Determination of saturated solution
Lesson 1: Know that at laboratory temperature (200C) 10g of water can dissolve up to 20g of sugar; 3.6g table salt.
a) Mix 15g of sugar into 10g of water, have we obtained a saturated solution? Why?
b) Mix 4.5g of salt into 10g of water, have we obtained a saturated solution? Why?
a) 10g of water dissolves up to 20g of sugar for 15g of sugar. So we get an unsaturated solution.
b) 10g of water dissolves up to 3.6g of table salt for 4.5 grams of salt. So we get a saturated solution.
3.1. Essay exercises
Question 1: How to make the process of dissolving solids in water faster?
Verse 2: What form does the solute exist in?
Question 3: Why is heating a solution also a method to make solids dissolve faster in water?
Question 4: When dissolving cooking oil in a gasoline cup, what role does gasoline play?
Question 5: When sugar is added to water and then heated, how does the solubility of sugar in water change?
3.2. Multiple choice exercises
Question 1: Select the correct answers
A. A solution is a homogeneous compound of a solvent and a solute
B. Sugar water is not a solution
C. Water-soluble cooking oil
D. There are 2 ways for solids to dissolve in water
Verse 2: Gasoline can dissolve
B. Cooking oil
C. Sea salt
Sentence 3: Two substances that cannot dissolve together to form a solution are
A. Water and sugar
B. Cooking oil and gasoline
C. Wine and water
D. Cooking oil and sand
Sentence4: The solute exists in the form
D. Solid, liquid, gas
Sentence 5: Why is it also a method to make solids dissolve faster in water?
A. Softening of solids
B. High pressure
C. At high temperatures, water molecules move faster, increasing the number of collisions between the molecules and the solid surface.
D. Due to high temperature
After the lesson to know:
- Hydrogen gas reacts with oxygen in its elemental form, the reaction is exothermic; Know that a mixture of hydrogen and oxygen is an explosive mixture
- How to burn hydrogen in air, know how to test pure hydrogen and safety rules when burning hydrogen, know how to write the chemical equation of hydrogen with oxygen.