Concentration and Reading
Solubility Curves
Concentrations of Solutions
• A measure of the amount of solute dissolved
in a solvent is concentration.
• Concentrated or Dilute? Solutions can be
described as being concentrated or dilute. But these two terms do not tell you the amount of solute that is dissolved.
• The next slide shows how to calculate
concentration.
Calculating concentration
What is the concentration of a solution that has 15g of salt dissolved in 175mL of water?
Step 1 one equation for finding concentration is the following:
concentration= grams of solute/ milliters of solvent
Step 2 Replace grams of solute and milliters of solvent with the value given, and solve
15g salt/ 175mL water = .2g/mL
1. what is the concentration of solution A if it has 55g of sugar dissolved in 500ml of
water?
2. What is the concentration of solution B if it has 36g of sugar dissolved in 144ml of
water?
1. concentration= grams of solute/ milliters of solvent
= 55g/500ml =.11g/ml of salt
2. concentration= grams of solute/ milliters of solvent
= 36g/144ml
=.25g/ml of salt
SOLUBILITY
FORMULAS
amount of solute amount of solvent
amount of solute amount of solvent
=
1.The solubility of a solid is
15g / 100g of water. How
many grams of the solid
must be dissolved in 1 kg of
water to make a saturated
solution?
SOLUBILITY PROBLEMS
amount of solute amount of solvent
amount of solute amount of solvent
=
15 g
---100g
=X
---1000g
X=150g
15g X 1000g 100g
SOLUBILITY
EXAMPLES
2. If you have 50g in 500g of water, using solubility from problem #1, is the solution saturated?
15g
---100g
=
X
---500g
X=75g is saturatedNo, 50 g is not saturated! 15 g x 500g
SOLUBILITY
EXAMPLES
3. The solubility of a solute is 5g/100g water at 20 C and 7.5g/100g water at 50 C. How much of the solute must be dissolved in 250g of water at 20 C to prepare a saturated solution?
5g
---100g
=
X
---250g
X=12.5g to prepare a
saturated solution
5g x 250g
SOLUBILITY
EXAMPLES
4. The solubility of a solute is 5g/100g water at 20 C and 7.5g/100g water at 50 C. If a saturated
solution is prepared using 200g water at 50 C, then allowed to cool to 20 C:
a. Will it still be saturated?
SOLUBILITY
EXAMPLES
Will it still be saturated? @ 50 C:
7.5g
---100g
=
X
---200g
X=15g to prepare a
saturated solution @
50 C
7.5g x 200g 100g
SOLUBILITY
EXAMPLES
Will it still be saturated? Now cool it to 20 C:
5g
---100g
=
X
---200g
X=10g to prepare a
saturated solution @
20 C
5g x 200g 100g
SOLUBILITY
EXAMPLES
Will it still be saturated? Now cool it to 20 C:
15g > 10g
@ 20 C so its
supersaturated!!
SOLUBILITY
EXAMPLES
How much will precipitate out?
5g
---100g
=
X
---200g
X=10g to prepare a
saturated solution @
20 C
7.5g
---100g
X
---200g
=
X=15g to prepare a
saturated solution @
50 C
SOLUBILITY
EXAMPLES
How much will precipitate out?
Formulas
amount of solute amount of solvent
concentration= grams of solute/
milliters of solvent
1. What is the concentratio of a solution
containing 7.8 g of MgCl2 in 725 mL of water?
Given 7.8g MgCl2 ; 725mL water
Work concentration= amount of solute milliters of solvent
=7.8gMgCl2/725mLwater
2. What is the concentration 160.0 g of
NaCl in 458mL water?
Given 160.0g NaCl ; 485mL water
Work concentration = amount of solute
milliters of solvent = 160.0gNaCl/485mL water
3. What is the concentration 35.0 g of
MgCl2 in 250mL water?
Given g MgCl2 ; 250mL water
Work concentration = amount of solute
milliters of solvent = 35gMgCl2/250mL water
The solubility of a solid is 15g / 100g of
water. How many grams of the solid must be dissolved in 1 kg of water to make a
saturated solution?
Given: 15g/100g of water ; 1000g of water work:
SOLUBILITY PROBLEMS
amount of solute amount of solvent
amount of solute amount of solvent
=
15 g
---100g
=X
---1000g
X=150g
15g X 1000g 100g
What is Solubility?
Solubility: the maximum amount of
solute that will dissolve in a certain amount of solvent at a given temperature
Solute = substance dissolved Solvent = does the dissolving
Example: __ grams of salt (NaCl) in 100 g
Temperature and Solubility
Temperature affects how much of the solute
can be dissolved by the solvent.
Note: Increasing the temperature does not always
increase the solubility…think about what happens to dissolved gas in your soda when its heated
Solubility curves: used to show how the
solubility of a substance changes with temperature.
Solubility Curves
Solubility indicates the amount of solute that will dissolve in a given amount of solvent at a specific temperature.
For this curve,
X-Axis
Temperature
Y-Axis
How Much Solute Dissolves in 100g of
Water
Various Lines
Solubility Curves
CO2
Saturated
Supersaturated
Using an available solubility curve, classify as
unsaturated, saturated, or supersaturated.
80 g NaNO3 @ 30oC
45 g KCl @ 60oC
30 g KClO3 @ 30oC
70 g Pb(NO3)2 @ 60oC
p er 1 00 g H 2 O unsaturated saturated supersaturated unsaturated
Describe each situation below. (A) Per 100 g H2O,
100 g NaNO3 @ 50oC.
(B) Cool solution (A) very slowly to 10oC.
(C) Quench solution (A) in an ice bath to 10oC.
unsaturated;
all solute dissolves; clear solution.
supersaturated;
extra solute remains in solution; still clear
saturated; extra solute (20 g)
How to use a solubility graph?
A. IDENTIFYING A SUBSTANCE ( given
the solubility in g/100 cm3 of water and the temperature)
•
Look for the intersection of the
solubility and temperature.
Using Solubility Curves
1) How much KNO3 would dissolve in
100g of water at 50oC?
2) How much NH4Cl would dissolve in
200g of water at 70oC?
3) At what temperature would 22g of
KCl be able to dissolve in 50g of water?
4) Which is more soluble (has a higher
solubility) at 40oC?
NH3 KClO3
84g 120g
Learning Check :
What
substance has a solubility of 90 g/100 cm3 in
water at a
temperature of 25ºC ?
Learning Check :
What substance has a solubility of 200 g/100 cm3 of water
at a temperature of 90ºC ?
Look for the
temperature or solubility
•
Locate the solubility curve needed and
see for a given temperature, which
solubility it lines up with and visa
versa.
Learning Check:
What is the solubility of potassium nitrate at 80ºC ?
• What is the
solubility of potassium nitrate at 80ºC ?
Learning Check :
At what
temperature will sodium
nitrate have a solubility of 95 g/100 cm3 ?
Learning Check:
At what
temperature will sodium
nitrate have a solubility of 95 g/100 cm3 ?
Learning Check:
At what
temperature will potassium iodide have a solubility of
230 g/100 cm3 ?
Learning Check:
At what
temperature will potassium iodide have a solubility of 130 g/100 cm3 ?
Using Solubility Curves:
What is the solubility of
sodium chloride at 25ºC in 100 cm3
of water ?
From the solubility graph we see that sodium chlorides solubility is 36 g.
SOLUBLE OR INSOLUBLE?
Soluble
:
able to be dissolved
Insoluble:
does not dissolve in solution (or
water)
Precipitate:
an insoluble solid formed when two
To read the
graph:
1. Find the line for the substance. 2. The
amount that dissolves at a given temp. is on the y-axis
.
How much KNO3
dissolves in 100g H2O at 50oC?
1. Find the line (red)
2. Find the temperature
and follow up to the line. (green)
3. Read across to the
y-axis and this is the answer. (blue)
4. Since it is above the
½-way between 80 and 90, 87g KNO3 will dissolve.
Unsaturated
supersaturated
Sa
tur
Types of Solutions:
Saturated solution: point on the line
Contains maximum amount of solute at given temp Contains what it should hold
Supersaturated: above the line
Contains more solute than a saturated solution Contains more than it should hold
Unsaturated: below the line is
Contains less solute than saturated solution Contains less solute than it could hold
.
SOLUBILITY GRAPHS
C o nc e nt ra tio n (g /1 00 g w at e r) temperature 140 120 100 80 60 40 2010 20 30 40 50 60 70 80
NaNO3
KBr
NH4Cl
KNO3
Na2SO3
To do Calculations:
To calculate how much extra has been dissolved:
Extra = Dissolved amt - saturated
in soln (given value) line value @ that temp.
To calculate how much more can be dissolved:
? Much more = saturated - given value line value @ that temp
Example 1:
How much less KCl is dissolved at 20oC than at 60oC in 100g H
2O?
Read the line value:
32g at 20oC
Subtract it from the
given value:
Example 2:
How much more KCl is required to
saturate the solution if 25g are dissolved
at 40oC?
Read the line value:
40g
Subtract the given
value:
Your turn! Use your graph
1. How much NaCl will dissolve in 100g H2O
at 35oC?
2. How much NH4Cl will dissolve at 50oC? 3. What is the solubility of SO2 at 25oC? 4. What is the solubility of potassium
chlorate in 100 grams of water at 35oC?
5. What is the solubility of potassium
6. What minimum temperature needed to dissolve 80 grams of sodium nitrate in 100 grams of
water?
7. What minimum temperature needed to dissolve 42 grams of potassium chloride in 100 grams of water?
8. What minimum temperature needed to dissolve 20 grams of KClO3 in 100 grams of water?
9. If 95 grams of potassium nitrate are mixed with 100 grams of water at 45ºC, how much will not
dissolve?
10. If 85 grams of potassium iodide are mixed with 100 grams of water at 0ºC, how much more must
11. If 55 grams of potassium chlorate are
mixed with 100 grams of water at 55ºC, how much will not dissolve?
12. If 125 grams of potassium iodide are
mixed with 100 grams of water at 10ºC, how much more must be added to
saturate the solution?
13. What is the solubility of potassium
14. What is the solubility of potassium chlorate in 100
grams of water at 35 oC?
15. What is the solubility of potassium iodide in 100
grams of water at 10 oC?
16. What is the minimum temperature needed to dissolve
80 grams of sodium nitrate in 100 grams of water?
17. What is the minimum temperature needed to dissolve
42 grams of potassium chloride in 100 grams of water?
18. What is the minimum temperature needed to dissolve
19. If 95 grams of potassium nitrate are mixed with 100
grams of water at 45 oC, how much will not dissolve?
20. If 55 grams of potassium chlorate are mixed with 100
grams of water at 55 oC, how much will not dissolve?
21. If 125 grams of potassium iodide are mixed with 100
grams of water at 10 oC, how much more must be added to saturate the solution?
22. If 85 grams of potassium iodide are mixed with 100
grams of water at 0 oC, how much more must be added to saturate the solution?
23. What is the solubility of potassium chlorate in 50
1. 35g NaCl 2. 50g NH4Cl 3. 8g SO2
4. 13g KClO3 5. 135g KI
6. 12 C 7. 50 C 8. 45 C
9. 80g KNO3 a 45 C; 95g KNO3 – 80gKNO3 = 10g KNO3
10. 125g KI a 0 C; 125g KI – 85 g KNO3 = 40g KNO3