L8 - Diffusion

• Chemistry
• Secondary Education

Lesson 1 - What is IGCSE Chemistry?

4

9

Lesson 8 - Diffusion

Today, I'm going to...

• know about diffusion in liquids and gases,
• be able to describe what happens during diffusion using the KPT, and
• understand why diffusion happens at different rates.

Lesson 8 - Diffusion

• I can define diffusion.
• I can describe the kinetic energy and movement of particles during diffusion. 
• I can describe the effect of higher relative molecular mass on the rate of diffusion of gases.
• I can describe the effect of lower relative molecular mass on the rate of diffusion of gases.

I am successful if...

• Prepare your blue or black pen.
• Open your Workbook on page 3.
• Complete Focus 2 and Practice 3.
• You only have 3 minutes to complete your responses.

Workbook Exercise

ANSWERS

ANSWERS

B

C

A

D

ANSWERS

B

C

A

D

impossible

Structures of solids, liquids and gases

KPT	SOLID	LIQUID	GAS
Kinetic energy of particles	Low energy	Medium energy	High energy
Motion of particles	Vibrating at a fixed position	Moving slide past each other	Moving freely and quickly
Arrangement of particles	Regular, in rows	Irregular	Irregular
Separation of particles	Close together, (all) touching	Close together, (some) touching	Far apart
Forces between particles	van der Waals forces	cohesive forces	NO force between particles

Kinetic Particle Theory

Kinetic energy

Motion 

Arrangement

Forces

Separation

Method

Investigating diffusion in liquids

1.  Add 20 cm3 of room temperature water to Petri dish A.
2.  Add 20 cm3 of warm water to Petri dish B.
3.  Using a spoon, simultaneously add a small amount of potassium permanganate to the middle of Petri dishes A and B.

In which water does the solid diffuse faster?

phet.colorado.edu

Method

Investigating diffusion of bromine in air

1.  Add two drops of liquid bromine to a test tube and put a rubber cork to seal it.
2.  Start the stopwatch immediately after closing.
3. Observe.
4.  Stop the stopwatch once the gas occupies the whole test tube.

How long do two drops of bromine liquid diffuse in a test tube?

Key Question: 

• Which fume has a greater rate of diffusion: hydrogen chloride or ammonia?

Background information:

• When ammonia and hydrogen chloride gases meet in a sealed tube, they react to form a white smoke ring of ammonium chloride. The mass of ammonia gas is 17.0 g/mol, and the mass of hydrogen chloride gas is 36.5 g/mol.

Hypothesis:

• ___________________________________________

SDA 1.2 (Practical): Investigating the rate of diffusion

Risks: 

• Corrosive [C] chemical: Hydrochloric acid
• Corrosive [C] chemical: Aqueous ammonia

Safety precautions:

• Wear a laboratory coat throughout the experiment.
• Tie your long hair.
• Avoid smelling the chemicals directly. WAFT, if required.
• Wear safety glasses throughout the experiment.
• Wear safety gloves.

Method

1.  Put the soaked cotton wool with hydrochloric acid in the bottom of the test tube using forceps.
2.  Put the soaked cotton wool with aqueous ammonia near the mouth of the test tube.
3.  Seal the test tube with a rubber stopper.
4.  Observe.
5.  Record your observations on the datasheet.

• I can define diffusion.
• I can describe the kinetic energy and movement of particles during diffusion. 
• I can describe the effect of higher relative molecular mass on the rate of diffusion of gases.
• I can describe the effect of lower relative molecular mass on the rate of diffusion of gases.

I am successful if...

Self-check

• Open your notebook.
• Look for this.
• Read.
• Reflect.
• Complete.

Name something you did not know before this lesson, 

but NOW you do!