Lesson 6 part 2 (Week 7) 18 March 2014

Gummi bear and diffusion experiments

Our osmosis experiment

Aim: To investigate the diffusion of water through a selectively permeable membrane by soaking gummi bears in tap water over a 24 hour period.

What would you expect to happen? (Hypothesis)

“If gummi bears are soaked in tap water, at room temperature for a total period of 24 hours, then water would diffuse into the matrix of the gummi bears causing them to swell up by XXX (your prediction) percent.”

Results Gummi bear Cooma

Width- start

Height- start

Width-24hrs

Height- 24hrs

1

2

3

4

5

6

7

8

Average

Gummi bear Qbn

Width- start

Height- start

Width-24hrs

Height- 24hrs

1

2

3

4

5

6

7

8

Average

Gummi bear Bega

Width- start

Height- start

Width-24hrs

Height- 24hrs

1

2

3

4

5

6

7

8

Average

Results

• Find the average for each campus, then for all campuses combined…compare the results are they similar/different?

• Find the average %age difference between before and after sizes of gummi bears for each campus and then for all campuses combined….compare results.

• Graph results….how?

Graph of results…..

Diffusion experiments

• How does viscosity affect diffusion (Cooma)?

• How does temperature affect diffusion (Qbn)?

• How does molecule size affect diffusion (Bega)?

Viscosity: The resistance of a substance to flow. For example, water has a lower viscosity than molasses and flows more easily.

Aim of the experiment

• Is a short concise statement of what you will do

• Starts with “To investigate….”

• Be specific (look at aim for osmosis experiment)

Construct a hypothesis to test

• A hypothesis is a prediction of what you will find if you do an experiment

• It is phrased as an if (I do this)…..then (I predict this will happen) statement

• Look at osmosis experiment hypothesis for an example

• “If……….(I do this)….then…..(prediction)…”

Example of results table (make sure you have a copy of your data!!)

Time Treatments (eg Cooma)

(1/2min)

(1min) (1 ½ min)

Extra columns (up to 5 in)

(24hrs)

Jelly 1

Jelly 2

Jelly 3

etc

Example of final results table

Time Treatments (eg Cooma)

(½ min)

(1min) (1 ½ min)

(add more columns for data up to 5 min)

(24hrs)

Jelly (average)

Dish liquid (average)

Water (average)

Graph your data……

• How would we do it???? (We are graphing a trend over time)…..

Writing up your report An experimental report includes two experiments (gummi bear prac and your campus’ diffusion experiment. Your report will have the following headings: • Introduction • Part A- Osmosis in gummi bears experiment

– Aim – Background (this is your homework, worksheet for week 5, Q3) – Hypothesis – Risk assessment – Materials & methods – Results – Discussion & conclusions (or recommendations)

• Part B- Diffusion experiment – (Include all sub headings as for part A)

• References • Appendices (log book & risk assessment)

Logbook

Reflections for 18 March 2014:

- Is it important to takes notes/ have a logbook handy during experiments…why/why not?

- Would it have been handy to have had pre-prepared data sheets handy on the day of the experiment (why/why not)?

- How could this experiment have been improved? Explain?

- What else could we test? How would we do it?