Acids And Bases Worksheet Page 2
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1
2C.
Third Homework:
C1.
Why is the Arrhenius Definition of Acids and Bases necessary for considering acid
strength?
C2.
What do you need to know in order to use Kw to calculate the concentration of H+ or OH-?
C3.
By the way, since it hasn’t been emphasized in this homework, how do you calculate pOH?
C4.
How is pOH related to pH?
D.
Fourth Homework:
D1.
How are monoprotic acids different that diprotic acids? Why is this important when doing acid-base
calculations?
D2.
What is the equality used when titrating?
D3.
Why was an indicator important when titrating our laboratory experiment?
E.
Additional.
E1.
How do Arrhenius Acids differ in definition from Bronsted Lowry Acids?
E2.
Why and how do acids and bases act as electrolytes?
E3.
What are Buffers? How are they used? What are natural buffers?
Self-Study Questions Answers:
A1.
Water. Water has a pH of 7.0, and dissociates into H+ and OH- very infrequently: 1 Mole of water will
have 1 x 10-7 H+ and 1 x 10-7 OH- in it. MEMORIZE that pH = -log [H+].
A2.
Very acidic, relatively.
A3.
Not necessarily. Remember, pH is defined by Hydrogen ion concentration. Therefore, more H+ means the
solution has a lower pH. However, a very concentrated weak acid could generate a lot of H+, even though
the acid is not a strong acid. (Practice: What is the pH of 10 M acetic acid? 1 M HCL?)
A4.
Yes, both solutions are 1 Molar.
A5.
PH 0, and 1 x 10 – 7 (antilog) H+.
B1.
Ideally, you can recognize salient acids. However, the Ka chart will also tell you the strength of an acid.
Weak acids have small Ka values. Strong acids have large Ka values.
B2.
If the acid is strong, we can calculate pH directly from the concentration of acid.
+
-
1 M HCL
1 M H
+ 1 M Cl
in water.
However, weak acids require the use of Ka.
+
-
1 M HC
H
O
.01 M H
and .01 M C
H
O
in water.
2
3
2
2
3
2
C1.
The Arrhenius Definition helps us conceptualize why water is needed for acid-base chemistry to occur. See
the hydronium ion when you write the Arrhenius definition of an acid out? Water really is important!
-14
Without it, acids and bases cannot ioniize into H+ or OH-. Therefore, Kw = 1.0 x 10
, since water
+
-
+
-
-14
ALWAYS allows only the same multiple of H
and OH
in solution. Therefore, [H
] x [OH
] = 1.0 x 10
,
always.
-14
C2.
Two things. First, you must remember that Kw = 1.0 x 10
. Second, you must know or be able
+
—
to calculate the concentration of [H+] or [OH-]. This latter value will be all the H
or OH
that an acid or
base contributes, respectively.
C3.
Remember that pAnything = -log [anything]. pOH = - log [OH-].
C4.
14 = pOH + pH. This is because both pOH and pH have scales from 0-14. Water has a pH of 7, and a
pOH of 7, also. .1 M HCl has a pH of 1 and a pOH of 13. .1 M NaOH has a pH of 13 and a pOH of 1.
+
+
D1.
Monoprotic acids donate 1 H
, diprotic donate 2 H
per acid molecule. Therefore, 1 M H
SO
has 2 M H+
2
4
since it is a strong diprotic acid. Weaker acids may donate 2 or more hydrogens, but remember that Ka is
used here (don’t worry about this, but each H on the acid has it’s own Ka value.).
D2.
Molarity Acid X mL Acid = Molarity Base X mL Base. mL could be L or any other volume measurement,
as long as the units are the same on both sides ( a property of an equality.)
D3.
The indicator, phenothalein, allowed us to determine when the solution had just become basic (it turned
pink) during our titration. This is the end-point of our titration, meaning that we have added just enough
base to neutralize the acid.
E1.
E2.
E3.
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