Water and Solutions Concentration. 2 9.1 Solutes, Solvents, and Water concentration: the amount of...
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Transcript of Water and Solutions Concentration. 2 9.1 Solutes, Solvents, and Water concentration: the amount of...
2 9.1 Solutes, Solvents, and Water
concentration: the amount of each solute compared to the total solution.
Concentration
3 9.1 Solutes, Solvents, and Water
Concentration
More solute Less solute
How can we express concentration quantitatively (with numbers)?
4 9.1 Solutes, Solvents, and Water
( )( )
( )
( )( / )
( )
( )(%) 100
( )
,
mass of solute gconcentration g L
volume of solution L
mass of solute gconcentration
m
mol
ass of solution
es of solute mmol
oleconcentration
volume of solarity M
n
g
utio L
Concentration
There are several ways to express concentration
5 9.1 Solutes, Solvents, and Water
Suppose you dissolve 10.0 g of sugar in 90.0 g of water. What is the mass percent concentration of sugar in the solution?
6 9.1 Solutes, Solvents, and Water
Concentration
Calculate the molarity of a salt solution made by adding 6.0 g of NaCl to 100 mL of distilled water.
7 9.1 Solutes, Solvents, and Water
What happens when you add 10 g of sugar to 100 mL of water?
sugar
100 mLH2O
10 g
Conc. (%) = 10 g/110 g
Solubility
Water molecules dissolve sugar molecules …
8 9.1 Solutes, Solvents, and Water
Then when two sugar molecules find each other, they will become “undissolved” (solid) again…
… then, they become redissolved in water again.
Solubility
9 9.1 Solutes, Solvents, and Water
This is an aqueous equilibrium! The solution is “saturated
Equilibrium
Solubility
saturation: situation that occurs when the amount of dissolved solute in a solution gets high enough that the rate of “undissolving” matches the rate of dissolving.
10 9.1 Solutes, Solvents, and Water
Temperature has an effect on solubility
Temperature and solubility
210 gsugar
100 mLH2O
20oC
Undissolved sugar
210 gsugar
100 mLH2O
30oC
All the sugar is dissolved
11 9.1 Solutes, Solvents, and Water
solubility: the amount of a solute that will dissolve in a particular solvent at a particular temperature and pressure.
12 9.1 Solutes, Solvents, and Water
Temperature and solubility
You can dissolve (a lot) more sugar at higher temperatures
13 9.1 Solutes, Solvents, and Water
Temperature and solubility
Sugar becomes “undissolved” (solid) as the temperature goes down
14 9.1 Solutes, Solvents, and Water
Temperature and solubility
Temperature does not have the same effect on the solubility of all solutes
15 9.1 Solutes, Solvents, and Water
Temperature affects:
- the solubility of solutes how much
- the rate of solubility how fast
16 9.1 Solutes, Solvents, and Water
Dissolving is a collision process
Slow (cold) molecules are not as effective as fast (hot) molecules
Salt dissolves faster in hot water
Dissolving rate
17 9.1 Solutes, Solvents, and Water
Dissolving rate
Substances are often ground up into powder to make them dissolve faster
A 1 cm cube has a surface area of 6 cm2
The same volume has a surface area of 9 cm2 when
divided up into smaller cubes
18 9.1 Solutes, Solvents, and Water
The rate of solubility increases:
- with an increase in temperature
- with an increase in surface area of the solute
19 9.1 Solutes, Solvents, and Water
Solubility of common gases in water at 25oC
At higher temperatures:
- solid solutes (like salt and sugar) are more soluble
- gases are less soluble
20 9.1 Solutes, Solvents, and Water
Seltzer water is a supersaturated solution of CO2 in water
supersaturation: term used to describe when a solution contains more dissolved solute than it can hold.
This solution is unstable, and the gas “undissolves” rapidly (bubbles escaping)
Hand warmer is a supersaturated solution of sodium acetate
This solution is unstable, and the particles “undissolve” rapidly turning into a solid and giving off heat