SOLUBILITY AND SOLUBILITY CURVES - PowerPoint PPT Presentation

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SOLUBILITY AND SOLUBILITY CURVES

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OBJECTIVE To investigate and explain the effect of structure and temperature on the solubility of solids in water Factors affecting solubility: 1. – PowerPoint PPT presentation

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Title: SOLUBILITY AND SOLUBILITY CURVES


1
SOLUBILITY AND SOLUBILITY CURVES
  • OBJECTIVE
  • To investigate and explain the effect of
    structure and temperature on the solubility of
    solids in water

2
What is Solubility?
  • Solubility the mass of solute which will
    saturate 100 g of solvent at a given temperature.
  • Unit - g per 100 g solvent (e.g.. Water,
    ethanol)
  • That means, if it takes 32 g of NaCl to saturate
    100 g of what at 25 0C, then its solubility is
    32 g per 100 g water at 25 0C.
  • The solubility of a solid in a liquid generally
    increases as temperature increases the hotter
    the liquid, the easier it is to dissolve the
    solid.

3
Solubility Curves
  • When solubility is plotted against temperature, a
    solubility curve is obtained.
  • The solubility at 58 0C
  • is 20 g per 100 g H2O
  • The solubility at 82 0C
  • is 40 g per 100g H2O
  • It will therefore take 40 -20 20 g
  • of the salt to re-saturate the solution
  • if the temperature is raised from 58 0C to 82 0C.

4
Reminder Some solids dissolve only slightly.
Other solids are very soluble - a lot can be
dissolved in a small volume of solvent. The
solubility of solids also depends on the
temperature of the solvent. Activity 1 Draw a
graph to show the solubility of potassium
nitrate, the figures are given below. Temperature
goes along the X-axis and solubility goes on the
Y-axis. Be sure to label your axes. Draw a smooth
curve through the points on the
graph. Temperature in C 0 20 40
60 80 100 Solubility in g/100g
water 13 32 64 110 169
246
5
  • Use the graph that to answer the following
    questions.
  • How many grams of potassium nitrate would
    dissolve in 100g of water at 50C?
  • 2. At what temperature is the solubility of
    potassium nitrate 200g per 100g of water?
  • 3. Imagine that you have heated 100 g of water to
    60C. You find that you can dissolve 110 g of
    potassium nitrate in it. If you now cool the
    water to 20C, only 32 g can stay dissolved in
    the water. What will happen to the other 78 g?
  • 4. If you heated 100 g of water to 80C, how much
    potassium nitrate could you dissolve in it?
  • 5. If you now cooled the solution to 40C, how
    much potassium nitrate would crystallize out?

6
  • 6. How many grams potassium nitrate would
    dissolve in 42 g of water at 20C?
  • 7. How many grams of water will it take to
    dissolve 75 g of KNO3 at 65C?
  • 8. What is the percent KNO3 in solution that is
    saturated at 70C?

7
Factors affecting solubility
  • 1. Temperature Solutes dissolve more easily with
    hot solvents than cold solvents.
  • Temperature is a measure of the kinetic energy of
    the atoms and molecules of a substance. The more
    heat energy a body possesses the greater the
    speed with which its molecules are moving and
    colliding, because of this the atoms of hot
    solvents are able to break apart the bonds
    holding solute molecules together more easily.

8
2. Pressure
  • Pressure is a factor to gases dissolved with
    liquids. The presence of gases with high pressure
    above a mixture containing dissolved gases
    prevents these gases from escaping.
  • E.g Opening a coke bottle relieves pressure and
    allows dissolved CO2 gases to escape from the
    liquid.

9
  • Fortunately for fish, oxygen is slightly soluble
    in water. A fish takes water in through its
    mouth. The water passes over the fish's gills,
    which are able to remove the dissolved oxygen.
    The water, minus the dissolved oxygen, then
    passes out through the gill slits.
  • Fizzy drinks contain a dissolved gas - carbon
    dioxide. It isn't a very soluble gas, so it is
    forced into the water under pressure. When you
    unscrew the top of a bottle of fizzy drink, the
    pressure is released and the carbon dioxide comes
    back out of solution. You see bubbles of gas
    streaming to the surface. Carbon dioxide is added
    to drinks to improve the taste. If you leave the
    top off a bottle, most of the carbon dioxide will
    be released and the drink will taste 'flat'.

10
3. Nature of the solvent
  • There are 2 main types of solvents
  • 1. Polar or charged
  • 2. non-polar or uncharged.
  • Polar/charged solvents dissolve solutes with
    charged particles. E.g H2O and NaCl. Non-Polar
    solvents dissolve uncharged substances. E.g. I2
    is dissolved by ethanol, hexane or other
    uncharged substances.

11
Concentration of solutions
  • A dilute solution contains more solvent than
    solute.
  • E.g. Sea water
  • A concentrated solution contains relatively more
    solute than solvent.
  • E.g. 95 HCl
  • A saturated solution contains as much solute as
    it can possibly hold at that temperature and
    pressure.
  • E.g. a Thoroughly stirred glass of juice will
    have some sugar left on the bottom of the glass.
    this indicates that the solvent water) is holding
    as much solute as it can hold.
  • A supersaturated solution contains more solute
    than it is supposed to hold at a given
    temperature and pressure.

Supersaturated solutions are rare and are
unstable, physically disturbing them can cause
excess dissolved solute to precipitate and fall
to the bottom.
12
Procedures which affect the rate at which
substances dissolve
  • Crushing
  • Stirring
  • Heating
  • Why?

13
  • Activity 2
  • Fill in the formula for each chemical, then
    calculate the difference column and answer the
    questions.

Name of chemical Formula solubility at 15C solubility at 80C Difference in solubility
Copper (II) sulfate 18.8 55.0
Potassium chloride 32.8 51.3
Potassium nitrate 25.8 169.0
Sodium carbonate 16.4 45.8
Sodium chloride 35.9 38.4
14
  • 1. Which is the least soluble at 15C?
  • 2. Which is most soluble at 15C?
  • 3. Which one is most soluble at 80C?
  • 4. Which one increases in solubility by the
    least?
  • 5. Which one increases in solubility by the most?

15
Activity 3 This table shows the solubility of
some gases in water. The solubility of a gas is
the mass in g that will dissolve in 1oo g of
water. The solubility is shown at three different
temperatures. 1. Which of the gases is
the most soluble? 2. Which of the gases is the
least soluble? 3. In what way is the effect of
temperature on the solubility of gases different
from its effect on the solubility of solids?
10 0C 20 0C 30 0C
NH3 8700 6800 5300
CO2 116 84.8 65.2
O2 3.7 3.0 2.6
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