# LAB TITLE Separation of Mixture

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```					                  Lab Title: Titration

The purpose of this lab is to:
PURPOSE            Determine the molarity of 2 different sodium
hydroxide (NaOH) solutions of unknown concentration
by titrating with a standard 0.1 M HCl solution
    Calculate percent error of results

MATERIALS       2 burettes                                2 different NaOH
   2 Erlenmeyer flasks (250 mL)            solutions of unknown
   0.1 M HCl solution                      concentration
   Phenolphthalein indicator                 Gloves (optional)

You experienced how to determine the approximate pH of a
PRE-LAB      solution by using pH indicators in the Household Chemicals lab.
DISCUSSION   What if you need to know the exact pH, or hydrogen ion
concentration, of a solution? As an example, environmental
scientists, studying the effects of acid rain, might need to
quantify the exact hydrogen ion concentration in Adirondack lake
waters.

There are several ways to quantify hydrogen or hydroxide ion
concentration. Hand-held electronic pH meters are often used.
An alternative, and much more colorful method, is called titration.

Page 1                                             ARHS Chemistry Dept.
When an acid and a base combine with each other, a neutralization
reaction occurs. The general form of the neutralization reaction
is:

acid + base  salt + water

Titration makes use of the neutralization reaction to quantify the
concentration of an unknown acid or base. The specific
neutralization reaction that you will conduct today is:

HCl + NaOH  NaCl + H2O

The figure on the left side of page 1 of your lab shows how pH
changes during the titration of a strong acid (such as HCl) with a
strong base (such as NaOH). The starting pH is low. As base is
added, the pH rises. The rise is pH is gradual at first. However,
when nearly all of the H+ ions from the acid are neutralized by the
base, the pH shoots up dramatically with the addition of a very
small volume of NaOH. This abrupt increase in pH occurs at the
equivalence point of the titration. By choosing a pH indicator that
changes color near the equivalence point, we get a visual cue at
that point in the reaction. The equivalence point for a strong acid
(one that ionizes completely) and strong base is pH 7.0. Weak
acid/base combinations have equivalence points near, but not equal
to, pH 7.0.

At the equivalence point, we know that the total number of OH-
ions is equal to the total number of H+ ions. Therefore, we can
apply the titration equation, shown below and in Reference Table
T, to figure out the concentration (aka molarity) of our unknown
solution.

Titration Equation:

MaVa = MbVb

Ma = molarity of acid                    M b = molarity of base

Va =   volume of acid                    Vb = volume of base

Page 2                                         ARHS Chemistry Dept.
CHECK FOR UNDERSTANDING:

1. 400 ml of a solution contains 2 moles of H+ ions. What is the molarity of
the solution? Show calculation with units: _________________________

2. Identify the products of this neutralization reaction:
HNO3 + KOH  ________ + ________

3. 50 ml of 0.2 M HCl is used to titrate 22 mL of an NaOH solution. Show a
correct numerical set up (including units) of the titration equation for this
situation:

4. Solve the equation above for the molarity of the base. Show all work and a
final result

______________M NaOH

PROCEDURE                      1. Work in teams of 2-3. Each partner does at least one
titration.
2. Deliver approximately 10 ml of acid into an Erlenmeyer
flask. Record initial & final burette readings on data
sheet to the nearest 0.01 ml and calculate net volume
of acid to the nearest 0.01 ml.
3. Add 1-2 drops of phenolphthalein to flask
4. Record initial base burette reading. SLOWLY add base
to acid while swirling until a light pink color is seen.
Record final burette reading and calculate net volume
of base added to the nearest 0.01 ml.
5. Use the titration equation to calculate the
experimental molarity of the base.
6. Ask your teacher for the actual molarity of your base.
Calculate percent error.
7. Repeat for a total of two bases – two trials per base.
Caution: Be sure to wear
safety goggles to protect
your eyes from acid/base..

Page 3                                                    ARHS Chemistry Dept.
Data Sheet 1

Base #_______                           Determine the molarity of the NaOH
Trial 1 of 2                                      Show all calculations here

0.10 M HCl    NaOH
Initial Volume
(ml):
+/- 0.01ml
Final
Volume (ml):
+/- 0.01ml
Volume
Delivered (ml)
+/- 0.01ml

Base #_______                           Determine the molarity of the NaOH
Trial 2 of 2                                      Show all calculations here

0.10 M HCl    NaOH
Initial Volume
(ml):
+/- 0.01ml
Final
Volume (ml):
+/- 0.01ml
Volume
Delivered (ml)
+/- 0.01ml

Page 4                                           ARHS Chemistry Dept.
Data Sheet 2

Base #_______                           Determine the molarity of the NaOH
Trial 1 of 2                                      Show all calculations here

0.10 M HCl    NaOH
Initial Volume
(ml):
+/- 0.01ml
Final
Volume (ml):
+/- 0.01ml
Volume
Delivered (ml)
+/- 0.01ml

Base #_______                           Determine the molarity of the NaOH
Trial 2 of 2                                      Show all calculations here

0.10 M HCl    NaOH
Initial Volume
(ml):
+/- 0.01ml
Final
Volume (ml):
+/- 0.01ml
Volume
Delivered (ml)
+/- 0.01ml

Page 5                                           ARHS Chemistry Dept.
Data Summary & Analysis

Base #:______                                           Base #:______

Trial 1 Molarity:                                  Trial 1 Molarity:

Trial 2 Molarity:                                  Trial 2 Molarity:

Average                                            Average
Molarity:                                          Molarity:

Actual Molarity                                    Actual Molarity
(from teacher):                                    (from teacher):

% Error:                                           % Error:
(show calculation                                  (show calculation
below)                                             below)
Calculation:                                       Calculation:

REAL LIFE CONNECTION

Medical and Pharmaceutical Analyses

Ever have blood drawn for testing after a doctor’s visit?? Chances are, a titration
process was used to analyze your blood. Many common blood tests, such as glucose
monitoring in patients with diabetes, are done colorimetrically using titration methods.
Urinalysis, such as pregnancy testing, is frequently based on titration. Doctors &
pharmacists use titration to determine the correct proportion of different medicines in
an intravenous drip. Most modern blood labs use automated titration equipment, but
the concepts behind the equipment are exactly those you did in this lab!

Page 6                                                         ARHS Chemistry Dept.
CONCLUSION

Type your conclusion in CEI format on a separate sheet of paper. You must use the
following vocabulary terms in a way that demonstrates their meaning:

     Neutralization                  Endpoint
     Titration                       Molarity
     Hydroxide ion                   Hydrogen ion
     alkaline                        acid

Be sure to UNDERLINE OR HIGHLIGHT each of the vocabulary words.

Page 7                                                   ARHS Chemistry Dept.

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