(salt water lab)

A shipwrecked sailor is stranded on a small desert island

with no fresh water to drink.

He knows he could last without food for up to a month, but

if he didn't have water to drink he would be dead within a

week.

Hoping to postpone the

inevitable, his thirst drove

him to drink the salty

seawater. He was

dead in two days.

Today we explore the cause of the sailor's

death.

We'll prepare solutions of salt water to represent

the sea, and we'll cut up slices of potato to

represent the sailor.

(Potatoes are made of

cells, as is the sailor!)

You’ll be writing this experiment up on your own

paper – so get out a piece of paper and start…

For a proper lab report you will need to include: • Your name & date • A Title • The Research question • A hypothesis • Diagram and description of experimental set up • Data table • Analysis – data converted to table or calculations - description of results • Conclusion – several paragraphs describing how

the results give an answer to the research question. Use results to support your claims.

• potato slices,

• cups,

• marker,

• paper towel,

• salt solutions,

• tap water,

• balance,

• clock,

• metric ruler,

• plastic wrap

Materials:

Procedure: Day 1

1. Get 4 cups and label them: 0%, 5%, 10%, 20%

2. Get a piece of paper towel that your cups will fit on and put

your groups’ name on it.

3. Get 8 potato cores.

4. Cut them into the same length, (approx. 5 cm each) Record

their length.

5. Organize your cores into pairs. Weigh (mass) each pair of

cores and record their mass in a data table.

6. Observe and then Record the turgidity of the potato

cylinders.

7. Place one pair of cores in each cup – be sure to note which

pair (based on their mass) was placed in which cup.

8. Pour the appropriate concentration of salt water (0% is tap

water) into each cup – just enough to cover the potatoes.

9. Put the cups on the paper towel and set aside for

Thursday.

Carefully remove the potato cylinders from the 0%

solution & pat them dry on a paper towel.

Measure and record the length of the potato

cylinders & the appearance of the cylinders.

Measure & record the mass of the pair of cylinders.

Repeat above steps for the remaining potato

cylinders in the other salt solutions.

When you are finished, throw the potato cylinders

away and clean up your equipment & area. Return

materials to their proper place.

Day 2

Data:

Calculate and graph %∆mass

%∆mass =(final mass - initial mass) / (initial mass) x 100%

Graph – trend line DRY MIX

Mass (g)

Conc. NaCl Trial 1 t = 0 24 hr

Trial 2 t = 0 24 hr

Trial 3 t = 0 24 hr

average t = 0 24 hr

0%

5%

10%

20%

Conc. NaCl

%∆m

0%

5%

10%

20%

Apply what you know

Do you think you would get similar results if you

used a sugar solution instead of a salt solution?

Make a Prediction and Test it!

Design a controlled experiment

• what will be your control?

• what are your manipulated (independent)

and responding (dependent) variables?