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Copyright © Houghton Mifflin Company. All rights reserved. 11–1
Different Units of Concentration
• We’ve talked about molarity in the past. You need to review molarity, keeping in mind electrolyte issues
• We talked about (or will talk about) molality in lab
• On the next slide, you’ll see these two as well as two other units that you need to be familiar with
Copyright © Houghton Mifflin Company. All rights reserved. 11–2
Solution Composition
1.Molarity (M) =
2.Mass (weight) percent =
3.Mole fraction (A) =
4.Molality (m) =
moles of soluteliters of solution
mass of solutemass of solution
100%
molestotal moles in solution
A
moles of solutekilograms of solvent
Copyright © Houghton Mifflin Company. All rights reserved. 11–3
Worksheet Problem
1. A sample of caffeine, was dissolved in 45.0 g of chloroform to give a 0.0946 m solution. How many grams of caffeine were in the sample? MM(caffeine)
= 194.1 g/mol.
Copyright © Houghton Mifflin Company. All rights reserved. 11–4
Q2(a)
2. A 0.688 m citric acid solution has a density of 1.049 g/mL. The molar mass of citric acid is 192.12 g/mol.
(a) Find the mass % of citric acid in the solution.
Copyright © Houghton Mifflin Company. All rights reserved. 11–5
Q2(b)
2. A 0.688 m citric acid solution has a density of 1.049 g/mL. The molar mass of citric acid is 192.12 g/mol.
(b) What is the molar concentration of citric acid?
Copyright © Houghton Mifflin Company. All rights reserved. 11–6
What is solubility?
• Solubility is the maximum concentration that a solute can attain in a given solvent at a given set of conditions (T & P, see sheet)
– Also: The concentration of a “saturated” solution (where dissolved and undissolved solute are in dynamic equilibrium)
What factors affect solubility [Part 1]?
• Because of “energetics”, if interparticle forces are similar in solute and solvent, dissolution occurs.– “like dissolves like”
Copyright © Houghton Mifflin Company. All rights reserved. 11–7
Copyright © Houghton Mifflin Company. All rights reserved. 11–8
Three Steps in the Dissolving Process(Recall “Hess’s Law”!)
1) Which processes should be: Endothermic? Exothermic?
2) What determines HOW exothermic Step 3 will be?
Self-Other IM forces!!
Copyright © Houghton Mifflin Company. All rights reserved. 11–9
Figure 11.2 a&b Dissolution Processes that are (overall) (a) Exothermic and (b)
Endothermic
It turns out…
• Mixing is generally favorable (2nd semester will address this more [but see p. 515-516 in Tro])
• So…(also see Table 12.2 in Tro)
– An exothermic dissolution will (always) occur– A slightly endothermic dissolution will occur– But a “prohibitively” endothermic,
dissolution will not occur
Copyright © Houghton Mifflin Company. All rights reserved. 11–10
Copyright © Houghton Mifflin Company. All rights reserved. 11–11
The Energy Terms for Various Types of Solutes and Solvents
H1(positive)
H2(positive)
H3(negative)
Hsoln (= sum)
Outcome
Polar solvent, polar solute
Large Large Large, negative
Small Solution forms
Polar solvent, nonpolar solute
Small Large Small Large, positive
No solution forms
Nonpolar solvent, nonpolar solute
Small Small Small Small Solution forms
Nonpolar solvent, polar solute
Large Small Small Large, positive
No solution forms
Other Factors Affecting Solubility
Copyright © Houghton Mifflin Company. All rights reserved. 11–13
Factors Affecting Solubility
• Structural Effects – IM forces of solute/solvent (already discussed)
– physical state of solute (see below)
• Pressure Effects– Significant for Gaseous solutes only
• Temperature Effects– Different for gaseous vs. solid solutes
Copyright © Houghton Mifflin Company. All rights reserved. 11–14
A Gaseous Solute
Copyright © Houghton Mifflin Company. All rights reserved. 11–15
Carbonation
Copyright © Houghton Mifflin Company. All rights reserved. 11–16
The Solubilities of Several Gases in Water As a Function of Temperature
Copyright © Houghton Mifflin Company. All rights reserved. 11–17
Lake Nyos in Cameroon
Copyright © Houghton Mifflin Company. All rights reserved. 11–18
The Solubilities of Several Solids as a Function of Temperature