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).