Warm upAdd to your Solubility Concept Map

Activity 46 Analysis

Acidic Neutral BasicHydrochloric

Acid Water Potassium Hydroxide

SpriteRubbing Alcohol Baking Soda in

Water

Vinegar Milk Ammonia

Lemon juice

1.Group the 9 (10) substances you tested

2. Which do you think is the most useful indicator? Explain your answer by considering the advantages of each indicator.

– Universal indicator and pH paper distinguish a range between acid, neutral, and base

– pH paper is more convenient because it is stored as dry paper

– Difficult to see universal indicator change color in a colored substance

– Phenolphthalein is much easier to define, but doesn’t help us distinguish between acidic and neutral, or even somewhat basic solutions

3. What happens to the pH of an acid or a base solution as you dilute it with water?

– It becomes closer to 7, or neutral

4. Do you think that dilution with water is a good method for treating industrial waste that contains an acid or base? Explain the reasons for your answer.

– It works to produce a neutral solution– It may not be a good method because it would

take a lot of water to dilute a large volume of acid to a neutral pH

Activity 46 Major Concepts• Reactions with indicator chemicals can

distinguish acids from bases in solution• The more you dilute an acid or a base,

the closer it becomes to being neutral• Using multiple indicators can improve the

accuracy in your results

Activity 47 Follow-up• Discuss in your groups the importance

of acids, bases, and pH measurement to people and the environment, and review your responses to analysis questions #1 and #2. Share your Venn diagrams for question #4 and discuss differences.

Analysis Question #1• In what ways can the pH or acidity of water

affect:– living things, such as fish?

• May lead to them being unhealthy and unable to reproduce.

• If the pH is beyond the range for survival (below 6 or above 7.5 for most fresh-water fish), they will die.

– people?• If drinking water is acidic, it can pick up metal from the

water pipes, such as lead.• This is dangerous to humans and can cause effects on

the brain or nervous system or death.

Analysis Question #2

a. A solution with a pH of 5 is ___times as acidic as a solution with a pH of 6.

b. A solution with a pH of 4 is ____ times as acidic as a solution with a pH of 6.

10

100

Analysis Question #4

Acids Bases

pH<7Sour

Turns litmus paper redReacts with metals

Not NeutralCan be corrosive

pH>7Bitter

Turns litmus paper blueFeels slippery

Analysis Question #5

• What do you predict will happen to pH when an acid and a base are mixed together?– Acids get less acidic when you add water– Bases get less basic when you add water– Both move toward a neutral pH of 7

Acidic Basic Neutral

pH range < 7 > 7 7

Common household examples

Vinegar, orange or lemon juice

Ammonia, detergents, bleach, or baking soda

Water, alcohol

Uses Preserving foods, making fertilizer, cleaning metals, refining petroleum, digesting food in the stomach

Making soaps, producing fertilizer

Hazards Harms wildlife, corrodes pipes, at high concentration corrodes skin

Harms wildlife, corrodes pipes, at high concentrations corrodes skin

Activity 47 Major Concepts

• Acids and bases are important in industry, agriculture, and household chemistry.

• The pH of water affects the ways it reacts with other substances and can affect organisms living in the water.

• The pH scale is non-linear

Title: Mixing an Acid and a Base

Read pg. C-91

Problem: What happens when you mix an acid and a base?

Initial Thoughts/Hypothesis:

Activity 48

• Indicators can be used to determine how acidic or basic solutions are.

• As acids or bases are diluted with water, they become more like water in terms of their pH, but it may take a tremendous amount of water to accomplish this.

• A pH indicator is a chemical that changes color in response to the concentration of hydrogen ions (H+ :acids) and hydroxide (OH- :bases) ions present.

What have you learned about acids and bases?

Acid Base Neutral

Phenolphthalein Colorless Bright Pink Colorless

Universal Indicator

Red or pink Blue Green

pH Paper Red or Orange-Red

Blue or Purple

Yellow-Green

In this activity you will…

• Begin by adding the base to the acid:– Stir thoroughly after adding each drop and

observe the color before adding the next drop.– Record your results in a data table or a format of

your choice• In part B, you will add the acid to the base:

– Before you begin, make a prediction on how many drops of HCl it will take to neutralize 10 drops of KOH

– Record your results

Procedure:Following procedure on pgs. C-92 to C-93

Data/Observation:Create your own data table to record

results. Include information on your control (distilled water w/ indicator) and observation after each drop added. You need a table for part A and part B

Class Results:Figure 1: Acid-Base Neutralization

Num

ber o

f Stu

dent

Pai

rs

5 10 15 20Drops of base to neutralize 10 drops of acid

Num

ber o

f Stu

dent

Pai

rs

5 10 15 20

Drops of acid to neutralize 10 drops of base

Figure 2: Acid-Base Neutralization

Discussion part A• What happens to the concentration

of ions in the mixture as it becomes more basic?

The hydrogen ion concentration in the acidic solution is high, which results in a low pH. Then, as base is added, the hydroxide ion concentration increases.

• Mixing an acid and a base to produce a neutral solution is called neutralization.

• An acid can neutralize a base and visa versa. In neutralization, a hydrogen ion and a hydroxide ion cancel each other out by combining to create a water molecule.

• What happens as the hydroxide ion concentration continues to increase as more base is added?

The hydroxide ions neutralize or “cancel out” the hydrogen ions and the pH gradually increases until you get to just the place where there is no excess of either hydrogen or hydroxide ions. At this point, the solution is neutral.

Part B Results

• Compare the 2 graphs• Why may there have been differences?• Why did it not take the same amount of

drops for both neutralizations?