Period 4 & 5 – Task 3
Write up:
(1) Title and Purpose
(2) Final step by step method that you used.
(3) Observations and results (you can use the
table to you put together in task 2 if you did
it on a separate piece of paper)
(4) Graph (you can use the graph you did in task
2 if you did it on a separate piece of paper)
(5) Conclusion
(6) Discussion
(7) Evaluation
Kumara Chips and Salt
Purpose/Aim:
Kumara Chips placed in solution with high
concentrations of salt (0.6 mol L-1 and 0.8 mol
L-1), will lose mass as the chips will lose water
due to osmosis. Kumara chips placed in
solution with lower concentrations of salt
(distilled water, 0.2 mol L-1 and 0.4 mol L-1)
will gain mass as the chips will gain water due
to osmosis.
Marking (A/M/E):
Purpose stating what will
happen to the chips in
respect to osmosis.
Marking (M/E)
Method:
A method includes:
valid
(1) Collect distilled water and salt solutions (0.2
molrange
L-1; IV - five
conc including distilled
0.4 mol L-1, 0.6 mol L-1, 0.8 mol L-1)
L-1
(2) Fill three of the plastic containers with 15 water
mL ofplus
the0.3
0.2mol
mol
or below
and A,
above
0.3
L-1 solution. Clearly label each container with
0.2 and
B and
mol L-1 (step 1);
C.
– masswater.
of chips
(3) Repeat with all the other solutions and theDV
distilled
(stepsize
6) &7
(4) Cut 15 kumara chips from the same kumarabefore
using the
after (step 10);
sized cork borer.
Repeats (step 2 & 4)
(5) Blot each chip with a paper towel.
- volume of
(6) Weigh each chip and place each one in eachOV
of the
plastic
solution
(step
2), same
containers. Record the weight of the chip and the plastic
kumara (step 4), same
container it has been placed in.
(7) Put the lid on each of the plastic container.shape/size chips (step
4), blotting dry before
(8) Place all the containers on the same place on
the back bench
weighing
(steps 5 &
so they all experience the same changes in temperature.
cover to stop
(9) Leave all the chips in the solution until next10),
period
( 24 hours)
evaporation (step 7),
(10) Remove each chip, blot it dry with a paper stated
towel and
reweigh
time (step 9),
it. Record the final weight against each of the plastic
temperature
containers. Use the same electronic scalessame
to ensure
(step 8), same scales
consistency.
(step 10).
Observations:
The chips in the distilled water
(0.0 mol L-1 salt concentration) looked
slightly larger and felt firm.
The chips in the 0.8 mol L-1 salt
concentration solution were soft and
flaccid.
Results:
Salt Conc
Mol L-1
O.0
mol L-1
Plastic
Container
A
B
C
0.2
mol L-1
A
B
C
0.4
mol L-1
A
B
C
0.6
mol L-1
A
B
C
0.8
mol L-1
A
B
C
Original mass
(g)
Final mass (g)
Difference in
mass (g)
% mass
change
Mean %
mass
change
Mean % change in mass of kumara chips in different salt
concentrations
Marking (M/E):
Sufficient data
(valid range, 5
conc’s and
repeats)
recorded and
processed to
show trend.
40
Mean % mass change
30
20
10
0
0
0.1
0.2
0.3
0.4
0.5
0.6
-10
-20
-30
Salt concentration (mol L-1)
Trend shown by
accurate
0.7
0.8
0.9
calculation of %
mass change AND
by the
appropriate
graph N.B. line is
curved not
straight.
Conclusion:
My results showed that the kumara chips
gained mass in distilled water and the
low salt concentrations (0.2 mol L-1) and
lost mass in the higher concentrations
of salt (0.4 mol L-1, 0.6 mol L-1,
0.8 mol L-1). This is almost what I
predicted except for the 0.4 mol L-1.
This happens because water
moves
in
Marking
(A/M/E):
Valid conclusion reached
and out of the kumara by osmosis.
based on the processed
data in relation to the
purpose of the
investigation.
Discussion:
Marking (M/E):
When the chips were put in distilled water they gain mass
because the chips gain water from the surrounding solution due
uses
to osmosis. The process of osmosis causes Discussion
a net flow of
water,
across the semi permeable membrane, along
the decreasing
knowledge
of the
water potential gradient from a solution with
a highofwaterprocess
osmosis to
potential to one with a lower water potential.
The chips
gain or
explain
the
trend
water because the distilled water has a higher water potential
pattern in the results:
than the chips.
- gained
mass, gained
The graph shows that in solutions with a salt
concentration
less
that 0.4 mol L-1 the water potential of thewater,
solution
inside
the
due
to osmosis
cell is still higher than that of the surrounding
salt
solution semi
so
(water
potential,
water moves into the kumara cells by osmosis.
In salt membrane,
solutions
permeable
of 0.4 mol L-1 the water potential of the solutions inside and
net
flow of
water,
outside the cell are very similar so we would
expect
very
littlewater
net flow of water into the kumara cells. potential gradient)
As the concentration of the salt solution increases
above
to in
- small mean
% 0.4
change
0.8 mol L-1 the potato chip loses more and mass,
more mass
small because
net water
the difference in water potential between flow
the inside of the
kumara cells and the surrounding solution is increasingly
loss
of mass,
water
different. This means that when the chips -are
placed
in the
higher concentration solutions more water loss,
will move
out
of the
due to
osmosis
chips as the result of osmosis.
Evaluation:
My results showed that the chips gained mass in low salt
concentrations but lost mass in high concentrations of
salt. This conclusion is justified because
I use(E):
a number of
Marking
ways to ensure I used the best method possible to make
my investigation a fair test. For example I used a cork
of close
the to
borer to make sure all the chips usedEvaluation
were cut as
investigation
by each
exactly the same shape as possible. This
meant that
justification
of theof
chip had the same surface area available
for diffusion
conclusionofinthe
terms
of
water across the semi permeable membranes
potato
cells. The repeats used showed similar
results
toused,
eachsuch
the
method
other.
as sufficient data,
A change made to my original methodappropriate
was to make
theof IV,
range
chips slightly smaller than planned. This
was because
I had
appropriate
processing
to get all 15 chips from the same kumara
could
usingso
% that
mass Ichange,
control the variable of water potential in cells in different
minimization or removal
kumara.
of sources of errors,
The method was carried out in a way that variables that
limitations,
could have changed the rate of osmosis,
such asbias.
evaporation and temperature, were controlled by covering
the plastic containers with a lid and keeping them in the
same area and conditions for 24 hours.