AcidBase Titration

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Acid/Base Titration

• Thurston High School Chemistry

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Introduction
When acids and bases are added together a
neutralization reaction takes place. An acid and
a base combine to produce water and salt. For
example nitric acid potassium hydroxide
water salt HNO3 KOH
HOH KNO3
The acid donates a proton (H) to the hydroxide
(OH-) of the base to form water.
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Q-1 Complete the following reaction. Have your
instructor check your answer
Hydrochloric acid sodium hydroxide
water salt HCl
NaOH
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To do a titration we use a buret
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Q-2 What is the unit of volume on a buret?
Q-3 What is the maximum volume that can be
measured with our burets?
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Using the burets

• Rinse your buret with distilled water

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• Gently pull the tip off and rinse it out also.

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• The buret with the red dot must be used for acids
  and the buret with the blue dot must be used for
  bases.
• Fill your burets to approximately 30 mL. Be sure
  there are no air bubbles in the tip of your
  buret. Record your beginning volumes on your
  paper.
• To read the meniscus you must be at eye level,
  and read at the bottom of the dip.

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• Holding a white card with a black line behind the
  buret can be very helpful

• Each line on our buret represents 1/10 of a mL so
  be sure to estimate your readings to .01 mL

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Q-4 What is the reading here? Have your
instructor check your answer.
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• To release liquid turn, the stopcock. Be careful
  to not pull out on the stopcock as you turn it.

Q-5 Use your buret to measure out exactly 4.50
mL of acid into a clean Erlenmeyer Flask. Have
your instructor check your results
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Q-6 In your answer to Q-1 the mole ratio of acid
to base is ____ _____
In a titration with this ratio we can use the
following relationship
Ma x Va Mb x Vb molarity of acid x
volume of acid molarity of base x volume of
base
Q-7 Write this formula on your paper
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In a titration we know the concentration of one
of the solutions. This is known as the standard
solution. We also can measure the volumes of
acid and base using the burets. Once we know 3
of the variables we can calculate the
concentration of the unknown acid or base.
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Ex. If 15.20 mL of 1.0 M HCl is added to 30.60
mL of NaOH, what is the concentration of the base?
Ma x Va Mb x Vb
1.OM x 15.20 mL Mb x 30.60 mL
0.49 M Mb
Q-8 If 22.15 mL of 0.5 M NaOH is added to 16.50
mL of HCl, what is the concentration of the acid?
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• The indicator phenolphthalein is used to tell
  when the acid and base exactly neutralize each
  other. This is called the endpoint of the
  titration.
• When phenolphthalein is added to an acid it
  remains clear. When it is added to a base it
  turns pink

Q-9 If your flask is clear you need to add more
______.
Q-10 If your flask is pink you need to add more
______.
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• As liquid is added to the Erlenmeyer flask always
  swirl gently

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• The endpoint of a titration is shown by a light
  pink color that stays for at least 30 seconds

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• We start a titration by adding 10 mL of distilled
  water and 3 drops of phenolphthalein to a clean
  Erlenmeyer flask. Do this now.
• Q-11 Record the beginning volumes of acid and
  base. Also record the molarity of the acid.
• Add approximately 10 ml of acid to the flask and
  begin to add base.
• The first time through a titration we add the
  base quickly to turn the solution pink. You can
  then a small amount of acid and then titrate to
  the light pink endpoint.

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• When you are close to the endpoint you often need
  to add very small amounts of acid or base. To do
  this, turn the stopcock just enough to have 1
  small drop of liquid hanging from the bottom of
  the buret.

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• Then touch the buret to the side of the flask

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• Then use your squirt bottle to wash the drop in
  while you continue swirling the flask.

Q-12 When you reach the light pink end-point,
record the final volume of acid and base. Show
your instructor the end point and have your paper
initialed.
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• Q-13 Calculate the molarity of the base using
  the formula Ma x Va Mb x Vb

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• The key to a successful titration is patience!
• Always use clean equipment
• Remember to record your beginning and ending
  volumes and read to .01 mL
• Read the meniscus correctly
• Use the formula Ma x Va Mb x Vb for a 11 mole
  ratio to calculate the concentration of your
  unknown solution

Good Luck