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

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


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


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.


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.


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?


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”



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!!


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



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


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


A Gaseous Solute


Carbonation


The Solubilities of Several Gases in Water As a Function of Temperature


Lake Nyos in Cameroon


The Solubilities of Several Solids as a Function of Temperature

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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