Concentration Activity Part 1
PSI Biology
Name__________________________
The concentration of a chemical solution refers to the amount of solute that is
dissolved in a solvent.
Once you have identified the solute and solvent in a solution, you are ready to
determine its concentration. Concentration may be expressed several different
ways, using g/ml, molarity, parts per million (ppm), or percent composition.
A concentration gradient is considered to be the difference in concentration
between two regions, or, the difference in the amount of solutes within a solvent
between two regions. To determine the movement of solutes or solvent between
two regions, we will consider the following scenario:
Low concentration
glucose
High concentration glucose
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Based upon the above scenario we would predict that glucose will move out of the
bag and into the beaker solution. Why? Because molecules will move down a
concentration gradient, or from a ____________________ concentration to a
_______________________ concentration assuming the membrane is ______________________ to
the molecule(s).
Suppose we need to determine specific concentrations rather than simply relative
concentrations such as “higher” or “lower”? One method we often use to calculate
the concentration of solutes on either side of the membrane is mass of solute per
volume of solvent, or grams/ml. Mass/volume is most often used when quantities
are small such as in a diffusion lab. Using this method, our determination of
concentration is more specific and our predictions about movements across a
membrane are more accurate.
Sample scenario and calculations:
Suppose we are provided with the following information:
 A dialysis bag solution is prepared and 10ml of the solution is poured into
the dialysis bag. Both ends are sealed. Within the bag is 5 grams of NaCl.
 A beaker solution is prepared and100 ml of the solution is poured into a
clean beaker. Within the beaker solution is 10 grams of NaCl.
 The dialysis tubing membrane is permeable to NaCl and to water molecules
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10gm NaCl in 100ml
H20
5gm NaCl in 10ml H20
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To determine whether diffusion will take place, and in which direction (into the
bag? Out of the bag?) we must determine the concentration of both solutions.
Beaker solution: mass of solute per volume of solvent is one quick way to make
these determinations.
NaCl 10 grams/100 ml water = 1g/ml NaCl
Bag solution: We use the same method of calculation to ensure that we can
compare concentrations with like units.
NaCl 5gm/10ml of water = .5 g/ml NaCl
Diffusion of NaCl: Comparing the concentrations inside and outside of the bag we
can predict that NaCl molecules will move from outside the bag to the inside of the
bag **assuming the bag is permeable to NaCl.
Practice:
Data for calculation
1. What is the concentration of a solution
in grams/milliliter when 80 grams of
sodium chloride, NaCl, is dissolved in
200 milliliters of solution?
Calculation and answer
2. A solution of sodium hydroxide, NaOH,
contains 2 grams of solute in 40ml of
solution. What is the concentration of
the solution in grams/ml?
3. A solution of sugar contains 35 grams
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of sucrose, C12H22O11 in 100 mL of
solution. What is the concentration of
the solution in grams/ml?
4. Inside of a dialysis bag is placed a
solution of 25 g glucose in 10ml of water.
What is the concentration of the bag
solution relative to glucose? (in g/ml)
5. In a beaker is poured a glucose
solution. This solution consists of 50g of
glucose in 100ml of water. What is the
concentration of the beaker solution
relative to glucose? (in g/ml)
6. In which direction will the net
diffusion of glucose, calculated in steps 4
and 5 above, occur? Why?
7. In which direction will the net
diffusion (osmosis) of water, calculated
in steps 4 and 5 above, occur? Why?
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