Activity 4

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Transcript Activity 4

Activity 48 Follow-up
• Discuss in your groups the difference in
results for each neutralization between
• Lack of consistency in drop size
• Error in counting
• Difficultly deciding which number of
drops gave a neutral solution if you
overshot the neutral color
• Contamination of equipment
Analysis Questions
1. What happens as you add an
acid to a basic solution or add
a base to an acidic solution?
• first becomes closer to neutral
• eventually when you add too
much, you overshoot the
neutral point
2. Which solution seems more
powerful in this investigation, the
acidic or the basic? Explain your
• acid seems more powerful
• takes more drops of base than
acid to produce a neutral
3. Based on what you know so far, which
do you think is a better way of
neutralizing an acid: distilling it with
water, or adding a base?
• dilution is better because you only need water
• when you add the base you are creating another
• neutralization is better, because dilution requires a
huge volume of water
• dilution because the change is more gradual and
there is less chance to overshoot neutral.
4. Given two solutions, how might you
a. Whether these solutions are acidic or
– test them with universal indicator solution or
pH paper
– blue = base, red = acid
b. Which is more acidic or basic?
– mix equal amounts together and test with
universal indicator
– the more powerful solution will show up with
the indicator
Background Information
• Both the HCl and the KOH are 1%
solutions by mass.
• There are different numbers of reacting
particles in the two solutions of the
same volume.
• The more powerful the solution, the
more capable it is of changing the pH of
the mixed solution.
Activity 48 Major Concepts
• When they react in the appropriate ratio,
an acidic solution and a basic solution
will neutralize each other.
• Substances react chemically with other
substances to form new substances.
For example, an acid reacts with a base
to form a neutral product.
• A change in pH is a chemical change.
Activity 49
A Model for Acid-Base
Read pg. C-94
Problem: How can acid-base
neutralization be described in a model?
Hypothesis/Initial Thoughts:
The model you will be using
• The 3 red As represent three acid
particles (in one drop of acidic solution).
• The 2 blue Bs represent two base
particles (in one drop of basic solution).
• These numbers represent the ratio of
acid and base particles, not the actual
number, which is many billions in a
• The whole class represents the
solution—that is, all the drops that
collectively make up a sample of
• For procedure step 1 your challenge is
to determine if the solution (the class) is
---Suggestion: form several small
neutral groups (groups w/ equal number
of acid/base particles)
• Raise your hand if you are not part of a
neutral solution.
• Is the overall solution neutral?
• What chemical, acidic or basic, would
make this a neutral solution?
• How many drops of it must be added to
make this a neutral solution?
• How would we prepare cards to represent a
neutralization in which a drop of basic
solution and a drop of acidic solution have
equal numbers of acid and base particles?
• Did the acid and base solutions in the
neutralization we performed earlier have
equal concentrations of particles per drop?
• Procedure steps 3 & 4:
• Read the instructions in your book and
draw the indicated diagrams in your lab
notebook. Label each drawing
according to the step number (3a, 3b,
4a, and 4b).
Analysis Questions
1. For the example in Procedure Step 1,
how many drops of base would be
needed to neutralize:
a. 2 drops of acid? Explain, or draw to show
your reasoning.
3 drops of base because the acid droplet
has 3 particles in it and the base droplet
has 2.
b. 10 drops of acid?
– 15 drops
– The acid droplet has 3 particles in it and the
base droplet has 2
10 x 3 = 30 and 15 x 2 = 30
c. 4 liters of acid?
– 6 liters of base
– The acid droplet has 3 particles in it and the
base droplet has 2 (even though the parts
are in liters)
4 x 3 = 12 and 6 x 2 = 12
5. Given that the HCl and KOH solutions
used in Activity 48 were 1% (each of
them contains one gram of solute per
100 grams of solution), how could you
explain that the ratio of particles per drop
of the neutral solution is not 1:1?
– HCl has more acid particles than KOH has
base particles per gram
– grams of each of the solutes don’t behave
the same
– It takes more KOH to neutralize HCl