The aim of this experiment was to investigate and determine the
osmolarity of potato tissue. As
seen on the graph above, the line of best fit does not intersect most of the
points on the graph. However, the graph does present a general trend: with the
glucose concentration rising, the percent mass change of the potato decreases.
According to the
processed data collected, the potatoes from the glucose concentrations of 0.2M,
0.4M, 0.6M, 0.8M and 1M all shrank in size which means they are hypertonic
solutions. When osmosis occurred, water moved out of the potato cell through
the selectively permeable membrane, went in the glucose solution in order to
dissolve the solvent concentration and reach an equilibrium. When the water
left the cells of the potato they shrank which explains the decrease in mass. When
there are more glucose particles more water is needed to leave the potato cells
which is why the higher the glucose concentration, the bigger is the decrease
in percent mass change. The data supports that because the average mass change for
the trials with 0.2M is -2.49% decreasing all the way to -33.5% for 1M.
On the other hand, the
glucose concentration of 0M is a hypotonic solution because the potatoes
increased in size. Water came into the potato cells during osmosis because the
solvent concentration was higher inside the potato cells than outside. Therefore,
the potato cells expanded which is why this is the only positive percent change
(2.07%) in all of the collected data.
The purpose of the lab
was to find an estimated value of the solution concentration of the potato
tissue or in other words, the osmolarity of the potato tissue. Osmolarity can
be measured only when the solution is isotonic, meaning in a state of equilibrium.
In an isotonic solution water would neither leave nor go into the potato cells,
therefore, there the change of mass should equal to zero. If 0M is a hypotonic solution
and the percent change is positive and from 0.2M up the percent change is
negative, we can conclude that the osmolarity number must be higher than 0M and
smaller than 0.2M. The exact number can be calculated using the equation of the
function of the line of best fit. Since the y-axis on the graph represents the
percent change in mass which needs to be zero in order to find the osmolarity,
we substitute y for 0 and then solve the equation. The final answer for the
osmolarity or solution concentration of the potato tissue is 0.068. This also
means that a glucose concentration of 0.068M will be an isotonic solution where
osmosis will not occur and change the mass of the potato cells.
The consequent decrease
in the percent change illustrates that the data is reliable and it also
compliments the scientific reasoning behind it. Using percent change in mass
rather than the actual mass change in grams is a better option for this lab
because it is more convenient to work with the percentages. Moreover, it makes
more sense when looking at the big picture and it is clearer to understand.