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Chapter 4

CHM 111 Chapter Notes - Chapter 4: Volumetric Flask, Ionic Compound, Chemical Equation

Course Code
CHM 111
Acevedo Orlando

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Water, the Common Solvent
A. Water’s polarity gives it the ability to dissolve compounds
a. Because oxygen has a greater attraction to electrons, shared electrons spend more
time by the oxygen giving it a partially negative charge.
b. Thus, the hydrogen atoms become partially positively charged
c. This unequal distribution results in a polar molecule
B. Hydration: positive ends of water molecule are attracted to anion of dissolving solid,
while negative ends are attracted to cations of dissolving solid, causing dissolving solid to
fall apart
C. The bonds between the dissolving solid are replaced by water-ion interactions
D. When ionic substances dissolve in water, they break up into the individual cations and
a. Ex: ammonium nitrate becomes NH4 and NO3
E. Different ionic compounds have different solubility based on their ions’ affinities with
each other and with water molecules
F. When an ionic solid dissolves in water, the ions are dispersed and are assumed to move
around independently
G. Nonpolar substances are not as soluble in water
a. Ex: animal fat
The Nature of Aqueous Solutions: Strong and Weak Electrolytes
A. Electrical Conductivity: ability to conduct an electric current
a. Solutions that conduct current efficiently contain strong electrolytes
b. Solutions that conduct current inefficiently contain weak electrolytes
c. Solutions that permit no current to flow contain nonelectrolytes
d. The extent to which a solution can conduct an electric current depends on the
number of ions present
B. Strong Electrolytes
a. Three classes:
i. Soluble Salts
1. Consists of an array of cations and anions that separate and
become hydrated when the salt dissolves
ii. Strong Acids
1. A substance that produces H+ ions (protons) when it is dissolved
in water
2. Virtually every molecule dissociates to give ions (100% of
molecules become ions)
3. Ex: HCl, HNO3, and H2SO4
iii. Strong Bases
1. Soluble compounds containing the hydroxide ion (OH-) that
completely dissociate when dissolved in water
2. Ex: sodium hydroxide and potassium hydroxide
b. Solubility: measured in terms of the mass of solute the dissolves per given volume
of solvent or in terms of the moles of solute that dissolve in a given volume of
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C. Weak Electrolytes
a. Weak acids
i. Only one percent of its molecules dissociate in aqueous solution
ii. Ex: HC2H3O2
b. Weak bases
i. Only one percent of its molecules dissociate in aqueous solution
ii. Ex: NH3
D. Nonelectrolytes
a. Do not produce any ions
b. Ex: ethanol and table sugar
The Composition of Solutions
A. Molarity: moles of solute per volume of solution (expressed in liters)
B. Dilution: when water is added to a known solution to achieve the molarity desired for a
particular solution
a. Typical calculations include determining how much water must be added to an
amount of stock solution to achieve a solution of the desired concentration
b. Moles of solution after dilution must equal moles of solute before dilution
c. Involves a pipet and a volumetric flask
i. 2 types of pipets
1. Measuring pipets- used to measure out volumes for which a
volumetric pipet is not available
2. Volumetric pipets
Precipitation Reactions: when two solutions are mixed, an insoluble substance sometimes forms;
that is, a solid forms and separates from the solution
A. Precipitate: solid that forms
B. Best way to predict the identity of the solid is to think carefully about what products are
possible. To do so, we need to know what species are present in the solution formed
when the reactant solutions are mixed.
C. Things to help us predict products:
a. When ions form a solid compound, the compound must have a zero net charge.
The products of this reaction must contain both anions and cations.
b. Most ionic materials contain only two types of ions: one type of cation and one
type of anion
D. Solubility Rules to Memorize
a. Most nitrate salts are soluble
b. Most salts of Na+, K+, and NH4+ are soluble
c. Most chloride salts are soluble. Notable exceptions are AgCl, PbCl2, and Hg2Cl2
d. Most sulfate salts are soluble. Notable exceptions are BaSO4, PbSO4, and CaSO4
e. Most hydroxide salts are only slightly soluble. The important soluble hydroxides
are NaOH, KOH, and Ca(OH)2 (marginally soluble)
f. Most sulfide (S2-), carbonate (CO32-), and phosphate (PO43-) salts are only
slightly soluble.
g. The terms insoluble and slightly soluble are mostly interchangeable
Describing Reactions in Solution
A. Molecular Equation: shows the reactants and products of the reaction but does not give a
very clear picture of what actually occurs in solution
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