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
pairs.
• 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
answer.
• acid seems more powerful
• takes more drops of base than
acid to produce a neutral
solution
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
product
• 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
determine:
a. Whether these solutions are acidic or
basic?
– 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
Title:
A Model for Acid-Base
Neutralization
Read pg. C-94
Problem: How can acid-base
neutralization be described in a model?
Hypothesis/Initial Thoughts:
The model you will be using
today:
• 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
drop.
• The whole class represents the
solution—that is, all the drops that
collectively make up a sample of
solution.
• For procedure step 1 your challenge is
to determine if the solution (the class) is
neutral.
---Suggestion: form several small
neutral groups (groups w/ equal number
of acid/base particles)
Begin
• 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?
AA
BB
• Did the acid and base solutions in the
neutralization we performed earlier have
equal concentrations of particles per drop?
Data/Observation:
• 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).
3a.
BB
A
3b.
A
A
+
BB
=
A/B
A/B
4a.
A
A A
B
4b.
A
A A
B
+
B
B
=
A/B
A/B
A/B
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