concentration of solutions ch 14.2-14.3 (rb) / chapter 16 (bb)
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Concentration of SolutionsCh 14.2-14.3 (RB) / Chapter 16 (BB)
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Heterogeneous Mixtures
A heterogeneous mixture is a mixture that does not have a uniform composition and in which the individual substances remain distinct.
Suspensions are mixtures containing particles that settle out if left undisturbed.
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Solutions are homogeneous mixtures that contain two or more substances called the solute and solvent.
Most solutions are liquids, but gaseous and solid solutions exist.
Homogeneous Mixtures
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Homogenous Mixtures
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Solutions
solution – a substance dissolved in a liquid.
solvent – the liquid, solute – the substance
being disolved.
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Water—The Super Solvent!
Water is an universal solvent. Water dissolves more solutes than anything
else! A dissolved solid falls apart into its individual
constituent particles, either ions or molecules. This explains why they are usually transparent.
http://www.youtube.com/watch?v=EBfGcTAJF4o&playnext_from=TL&videos=gRLBCOaBXS0
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Factors that affect solubility
Like tends to dissolve like. Polar solvent dissolves polar solutes Non-polar solute dissolves in non-polar solvents
Molecular Size: Big, heavy molecules tend to be less soluble than small
light molecules. It is harder for the solvent to “cage” the solute.
Temperature: As temperature rises, agitated molecules or ions break
their bonds more easily. So as temperature goes up, so does solubility.
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Solution Equilibrium
The maximum concentration of solute that a solvent can hold at a certain temperature is called saturated solution.
If large amounts of solute are added to a solution at high temperature then allowed to slowly cool down, then a super saturated solution may occur.
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Concentration
The concentration of a solution is a measure of how much solute is dissolved in a specific amount of solvent or solution.
Concentration can be described as concentrated or dilute.
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Concentration
Concentrated vs. Dilute Concentrated: lots of solute per unit of
volume. Dilute: little solute per unit of volume.
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Concentration Units
Dilute and Concentrated can be ambiguous. What is dilute? What is concentrated? Chemists like their numbers!
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Example Problem p. 149
If 18.0 grams of sodium sulfate are dissolved in 207.0 grams of water, what is the percent concentration of this solution?
X 100
= 8.00% = x 100
% by mass = g solute g solution
18.0g solute
225g solution
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Molarity
Molarity is the number of moles of solute dissolved per liter of solution.
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Example Problem #1 p. 142
Calculate the molarity of 1500 ml of solution that contains 200.0g MgCl2.
200.0g MgCl2 1molMgCl2 1000 ml 1500ml 95.2g MgCl2 1 L
=1.40mol/L or M
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Example Problem #2 p. 142
Calculate the molarity of a 500 cm3 solution that contains 10.0 g of sodium hydroxide.
To solve: Convert 10.0 g of NaOH per 500 cm3 to moles of NaOH per dm3 of soultion.
10.0g NaOH 1 mol NaOH 1000 cm3
500 cm3 40.0 g NaOH 1dm3
Answer: 0.500 mol/dm3 = 0.500 M
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Dilutions
If you want a solution of lesser concentration you will need to dilute it! Add more solvent! The total number of moles of solute does not
change
M1 x V1 = M2 x V2
M = Molarity & V = VolumeM1 and V1 = “old” or stock
M2 and V2 = “new” or dilute
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Example #1
It is necessary to make a .500M solution of HCl from 250.0 ml of a 2.00M solution of HCl. What is the volume of the new solution?
M1 x V1 = M2 x V2
2.00M x 0.250 L = 0.500M x V2
V2 = 1.00 L
So… you add enough solvent to bring the new volume up to 1L. How much do you add?
1.00 L – 0.250 L = 0.750 L
solve for V2 = 2.00M x 0.250ml 0.500M
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THE END
Questions??? HW
BB Chpt 16: 1 (a-c), 2 (a-c), 10 (a-c), 13 Chpt 18: 1-3 a-c, 10 a-c