CHEM 141 Unit 4
Which side does the equilibrium lie in a reaction involving a weak electrolyte?
Left
Why are acids proton donors?
because H+ consists of ONLY a proton
What happens when a reactive metal is oxidized?
it is oxidized to a cation
What can molarity be used as?
a conversion factor between moles and liters
What is the oxidation number of nitrogen in nitric acid, HNO3?
+5
What is solvation?
the stabilization of the solute by solvent
Which solute will cause a light bulb to glow most brightly? (a) CH3OH (aq) (b) NaOH (aq) (c) CH3COOH (aq) (d) Cannot determine from the figure
(b) NaOH (aq)
What dissolved species are present in a solution of NaClO4? (a) H2O (l) (b) Na+ (aq) and H2O (l) (c) ClO4 - (aq) (d) Na+ (aq) and ClO4 (aq)
(d) Na+ (aq) and ClO4 (aq)
What is the equation of molarity?
(moles of solute)/(volume of solution in liters)
What are the rules to assign Oxidation Numbers?
1) Atoms in their elemental form have an oxidation number of zero 2) The oxidation number of a monatomic ion is the same as its charge 3) Alkali metals (group 1A on periodic table) have an oxidation number of +1, alkali earths (2A) +2, and the Al group (3A) +3 in ionic compounds 4) Nonmetals usually have negative oxidation numbers, although they sometimes can be positive: - Oxygen: usually -2, except in the peroxide ion (O2 2-), where it is -1 - Hydrogen: usually +1 when bonded to a nonmetal and -1 when bonded to a metal - Fluorine: -1. Other halogens: usually -1, unless combined with oxygen (oxyanions), where they will be positive 5) A neutral compound must have total oxidation state of zero
Name the different ways substances can be dissolved.
1) Dissociation 2) Solvation
One commercial method used to peel potatoes is to soak them in a NaOH solution for a short time and then remove the potatoes and spray off the peel. The NaOH concentration is normally 3 to 6 M, and the solution must be analyzed periodically. In one such analysis, 45.7 mL of 0.500 M H2SO4 is required to neutralize 20.0 mL of NaOH solution. What is the concentration of the NaOH solution?
2.28 M
How many grams of Na2SO4 are required to make 0.350 L of 0.500 M solution of Na2SO4?
24.9 g
What is the oxidation number of N in NH3?
3-
We just determined that to make 0.350 L of 0.500 M solution of Na2SO4 one needs 24.9 g of Na2SO4. How many grams of Na2SO4 are required to make 3.5 L of 0.10 M solution of Na2SO4?
50. g
Where would you place a negative ion relative to the water molecule?
A negative ion is attracted to the positively charged part of the water molecule
Where would you place a positive ion relative to the water molecule?
A positive ion is attracted to the negatively charged part of the water molecule
Why isn't Al(OH)3 classified as a strong base?
Al(OH)3 is insoluble in water
What are strong bases?
Bases that dissociate to metal cations and hydroxide anions in water
How can the molarity of a new solution from dilution be determined?
M(new) = M(old) x [v(old)/v(new)]
How can neutralization reactions be written?
Molecular, complete ionic, or net ionic equations
Which ions, if any, are spectator ions in this reaction? AgNO3 (aq) + NaCl (aq) --> AgCl (s) + NaNO3 (aq)
Na+ (aq) and NO3- (aq)
Do substances have to contain OH- to be a base?
No
What are neutralization reactions?
Reactions between an acid and a base
Which side does the equilibrium lie in a reaction involving a strong electrolyte?
Right
If a substance is ionic, is it a strong electrolyte or a weak electrolyte?
Strong electrolyte
How is the molarity of 0.50 M Kbr solution changed when added to double its volume?
The new concentration is 0.25 M
What are weak bases?
bases that partially react to produce hydroxide anions
How do you determine if an oxidation-reduction reaction has occurred?
We assign an oxidation number to each element in a neutral compound or charged entity
Does a reaction occur when an aqueous solution of NiCl2 (aq) is added to a test tube containing strips of metallic zinc?
Yes
What does a chemical equilibrium indicate?
a reaction that can go both forward and backward
What is a precipitation reaction?
a reaction that occurs when two solutions containing soluble salts are mixed and an insoluble salt is produced
When a carbonate or bicarbonate reacts with an acid, what are the products?
a salt, carbon dioxide, and water
What is a standard solution?
a solution of known concentration
What is an aqueous solution?
a solution when water is the solvent
What is a strong electrolyte?
a substance that dissociates completely when dissolved in water, and can carry current
What is an electrolyte?
a substance that dissociates into ions when dissolved in water. It can carry current
What is a non-electrolyte?
a substance that may dissolve in water, but it does not dissociate into ions when it does so
What is a weak electrolyte?
a substance that only dissociates partially when dissolved in water
What are strong acids?
acids that completely dissociate in water
What are weak acids?
acids that only partially dissociate in water
What are solutes?
all other substances
What is titration?
an analytical technique in which one can calculate the concentration of a solute in a solution
Where is the reaction complete?
at the equivalence point
The number of moles is the same as the number of?
atoms or molecules
How can a solution be diluted?
by adding only solvent
How do all substances dissolve?
by solvation
How do ionic compounds dissolve?
dissociation
Which direction does a strong electrolyte proceed more rapidly?
foward direction
what is reduction?
gain of electrons
The solvent is present in ___________________
greatest abundance
What are solutions?
homogeneous mixtures of two or more pure substances
Classify these ionic compounds as soluble or insoluble in water: lead sulfate, PbSO4
insoluble
Classify these ionic compounds as soluble or insoluble in water: sodium carbonate, Na2 CO3
insoluble
Elements high on the activity series will exist as __________?
ions
What are "Spectator" ions (or molecules)?
ions or molecules that are unchanged on both sides of a chemical reaction
What are redox reactions?
oxidation-reduction reactions
Some metathesis (exchange) reactions do not give the __________________?
product expected
Oxidation cannot occur with what?
reduction
Why can't molecular compounds react with water?
some molecular substances react with water when they dissolve
What are always strong electrolytes?
strong bases
What are acids?
substances that ionize in aqueous solution to form H+
What are bases?
substances that react with, or accept, H+ ions; they increase the concentration of OH- when dissolved in water
What is concentration?
the amount dissolved in a solution
In dilutions, what happens to the concentration and moles?
the concentration is lower, but the moles don't change
What will the elements below on the activity series exist as?
the element
Which elements are more reactive on the activity series?
the elements high on the activity series
What is oxidation?
the loss of electrons
What is molarity?
the quantity of solute in a solution
What is the equivalence point based on?
the seen end point (color change)
What is a precipitate?
the solid that results from precipitation reactions
What is an oxidation-reduction reaction?
the transfer of electrons
What is standard solution used to determine?
the unknown concentration of another solution
Do molecular compounds dissociate?
they interact with water but most do not dissociate
What happens to ions in displacement reactions?
they oxidize and element, and they are displaced in a solution
What will the elements above hydrogen react to and produce?
they will react with acids to produce hydrogen gas
When the base of a neutralization reaction is a metal hydroxide, what is is produced?
water and a salt (an ionic compound)
How does a strong electrolyte dissociate?
when mixed with water
What is dissociation?
when water surrounds the separated ions