Transcript Activity 46: Investigating Solutions of Acids and Bases

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?
• It 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.
• The acid seems more powerful
because it takes a greater
number of drops of base than
acid to produce a neutral
solution.
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.
3. Based on what you know so
far, which do you think is a better
way of neutralizing an acid:
diluting it with water, or adding a
base? Explain your answer.
• Dilution because you only need water.
• Neutralization because dilution requires
a huge volume of water.
• Dilution because the change is more
gradual and there 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. If it turns blue, it
is a base, and if it turns red, it is an
acid.
b. which is more acidic or basic?
• Mix equal amounts together and test
with universal indicator. Whichever one
is more powerful will show up with the
indicator. If it turns blue, the base is
more powerful. If it turns red, the acid is
more powerful.
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
Neutralization
Read pg. C-94
Challenge:
How can acid-base neutralization be
described in a model?
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?
• Did the acid and base solutions in the
neutralization we performed earlier have
equal concentrations of particles per
drop?
Data/Evidence:
• 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).