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.

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

4. Given two solutions, how might you determine:

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.

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:

Activity 49

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?

AA BB

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.

3b.

+ =

A BB

A BBAA/BA/B

4a.

4b.

+ =

BA

A A

BA

A A B

B

A/B

A/BA/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

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)

10 x 3 = 30 and 15 x 2 = 30

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