Biology 12—Osmosis Lab (Sucrose)Purpose: In this experiment you will use dialysis tubing to investigate the relationship between solute concentration and the movement of water through a selectively permeable membrane by the process of osmosis.

Materials (per group)1) two 30 cm pieces dialysis tubing2) 40 mL of assigned sucrose solution3) 100 mL of unknown concentration sucrose solution4) 25 mL graduated cylinder5) funnel6) thread7) two 250 mL beakers8) paper toweling9) electronic balance

Procedure:1) Obtain two 30 cm long pieces of pre-soaked dialysis tubing.2) Tie off one end of each piece with thread to form a bag. Tie tightly. Use a funnel

to pour 20 mL of ONE of the following solutions into each bag. (a solution will be assigned to you) You will have two identical dialysis bags.

a. 0 Mb. 0.5 M sucrosec. 1.0 M sucrosed. 1.5 M sucrosee. 2.0 M sucrose

3) Remove most of the air from the bags by drawing the dialysis bags between two fingers. Tie off the other end of the bag leaving sufficient space for the expansion of the contents.

4) Use a graduated cylinder to measure out 100 mL of water and add to a 250 mL beaker. DO NOT JUST USE THE MEASUREMENT ON THE SIDE OF THE BEAKER. Repeat with the unknown sucrose solution and your other 250 mL beaker.

5) Thoroughly blot the outside of the bags with a paper towel and find the initial masses. RECORD.

6) Immerse one bag in each beaker and allow to stand for 20 minutes. Swirl every 5 minutes.

7) At the end of 20 minutes, remove the bags from the beakers. Thoroughly blot the outsides to remove excess water and determine the final masses. RECORD.

8) Record your results on the board. You will obtain the results for the other four solutions from your classmates.

9) Use the following formula to calculate percent change in mass for your data table:

% change = final mass − initial massinitial mass

× 100

Data & Observations-include qualitative (descriptive) observations

-ex: the bag increased in mass in the known solution and decreased in mass in the unknown-include quantitative data in your recopied version of the following table:

Contents of

dialysis tube

Initial mass (g) Final mass (g) Percent change in mass (%)

Water ? M Water ? M Water ? M

0 M

0.5 M

1.0 M

1.5 M

2.0 M

Analysis: Answer the following in detail, in complete sentences in your formal report.1) Plot the relationship between sucrose molarity (Y-axis) and % change in mass (X-

axis). Do this on an entire sheet of graph paper. Note: Plot both lines on the same graph!Ie

2) Why do some dialysis bags lose mass? Use appropriate vocabulary terms in your answer.

3) Why do some dialysis bags gain more mass than others?4) Use your graph to find the molarity of the unknown sucrose solution. Hint: what

should the change in mass be if the two solutions are the same strength?

Conclusion:-summarize the main points of theory that his lab demonstrates-explain how you were able to find the molarity of the unknown solution.-describe any sources of error you may have encountered in this lab.-explain any unusual results

Name Block Science Lab Checklist

Use and Attach this to the front of each lab report Check if done

Teacher feedback

Organization1. Name, Block, Date, Lab Partner in top right hand corner of page2. Lab is typed or written neatly in blue or black pen3. Lab report is sequenced in same order as this checklist, each section is

followed by an empty line, section headings are underlined.4. Title describes what lab is about and is underlined.

Lab Question5. Clearly states what we are trying to find out in the lab.

Hypothesis6. Directly answers lab question based on what you believe. 7. Well written in a complete sentence. Use third person.

Materials8. All materials are included (must be written out)9. Organized in a bulleted or numbered vertical list format

Procedure10.Written in the following format: “As listed on page _____ in (book name

or name of lab handout), steps ______ to _______”11.Describes any changes made to given procedure

Data & Observations12.Data table has appropriate title and each column heading has a title.13.Units are included (at top of column heading if appropriate)14.All observations are recorded as requested15.Each observation refers to a procedure step number16.All work is shown for calculations, numbers are formatted correctly

(usually rounded to 1 decimal place).17.Diagrams are formatted correctly (refer to diagram format handout)

Graph (If included)18.Title includes plotted variables (dependent, y, versus independent, x).19.Each axis has its own separate title, numbers clearly stated, & units

clearly stated.20.Legend is present (if more than one item shown)21.Appropriate scale is used (graph uses MOST of GRAPH PAPER)22.Data is plotted correctly. Correct variables are on correct axis23.Best fit line is used.

Analysis24.All answers are in complete sentences25.All work is shown with formulae and units for any necessary

calculationsConclusion & Sources of Error

26.Hypothesis is clearly repeated; for example “The hypothesis that...”27.Reasons to support of reject the hypothesis are given (should be from

data)28.Sources of error are included.29.Sources of error explain HOW they may have affected the observations.