warm up add to your solubility concept map. activity 46 analysis acidicneutralbasic hydrochloric...
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Warm upAdd to your Solubility Concept Map
Activity 46 Analysis
Acidic Neutral Basic
Hydrochloric Acid
WaterPotassium 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
Nu
mb
er
of S
tud
ent P
airs
5 10 15 20
Drops of base to neutralize 10 drops of acid
Nu
mb
er
of S
tud
ent P
airs
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?