Toxins Unit

Investigation IV: Neutralizing ToxinsLesson 1: HeartburnLesson 2: Watered DownLesson 3: pHooey!Lesson 4: Proton ShuffleLesson 5: Neutral TerritoryLesson 6: Drip DropLesson 7: Call Poison Control

Toxins Unit – Investigation IV

Lesson 1:

Heartburn

Unit IV • Investigation IV-X

ChemCatalyst

Countless products are advertised on TV with the promise of reducing acid indigestion.

• What is acid indigestion? What is acidity?

• What does acid have to do with your stomach?

• How do you think acid “reducers” work?

The Big Question

• What are some characteristics of solutions that are acidic, basic, or neutral?

You will be able to:

Describe the differences among acidic, basic, and neutral solutions.

• Indicators: A set of substances that respond to other substances with vivid color changes.

Activity

Purpose: This activity will introduce you to a special category of solution.

(cont.)

Safety note: Do not get acids and bases on your skin. In case of a spill, rinse with large amounts of water. Wear goggles.

(cont.)

Substance Formula Cabbage Juice

Indicator color

Indicator number

table salt (aq) NaCl

vinegar (aq) C2H4O2

rubbing alcohol C3H8O

ammonium hydroxide (aq)

distilled water H2O

stomach acid (aq) HCl

washing soda (aq)

Na2CO3

lemon juice C6H8O7

drain cleaner (aq) NaOH

(cont.)

Observations when added to CaCO3

stomach acid

vinegar

drain cleaner

(cont.)

Making Sense

• Look for patterns in the names, chemical formulas, uses, and properties of the substances you tested.

• List four characteristics of acids.

• List four characteristics of bases.

Indicators can be used to identify substances that are acidic, basic, and neutral when dissolved in water.

• Acids turn cabbage juice pink and are between 0 and 7 on the universal indicator scale.

• Bases turn cabbage juice green or blue and are between 7 and 14 on the universal indicator scale.

• Neutral substances do not change color with cabbage juice and are at or very near 7 on the universal indicator scale.

(cont.)

• pH scale: A number line from 0 to 14. The numbers are associated with indicator colors.

• The numbers associated with indicator colors are also called pH numbers or simply pH.

(cont.)

Check-In

• An unknown substance is purple with cabbage juice and does not react with calcium carbonate. Is it an acid, base or neutral substance? Explain.

Wrap-Up

• Acids and bases are different types of solutions and are classified according to their observable behavior.

• Acids and bases respond differently to indicators. Depending on the indicator, different colors will form that show either an acidic or basic substance.

Lesson 2:

Watered Down

ChemCatalyst

• Describe what you observe in the three vials.

• What is one explanation for the differences you observe?

• If you tested each solution with universal indicator before putting in the gummy bears, what colors would you expect to see?

The Big Question

• How does dilution affect the acidity or basicity of a solution?

Explain how dilution affects the concentration and pH of a solution.

Activity

Purpose: In this activity you will examine the effect of concentration on acidity and basicity of solutions.

(cont.)

Safety note – Do not get acids and bases on your skin. In case of a spill, rinse with large amounts of water. Wear goggles.

(cont.)

Well # Concentration Color pH number

1.0 M HCl

0.10 M HCl

0.010 M HCl

0.0010 M HCl

0.00010 M HCl

0.000010 M HCl

0.0000010 M HCl

0.00000010 M HCl

0.000000010 M HCl

Data Table for dilution of 1.0 M HCl

Data Table for dilution of 1.0 M NaOH

Well #

Concentration Color pH number

1.0 M NaOH

0.10 M NaOH

0.010 M NaOH

0.0010 M NaOH

0.00010 M NaOH

0.000010 M NaOH

0.0000010 M NaOH

0.00000010 M NaOH

0.000000010 M NaOH

Data Table for dilution of 1.0 M NaCl

Well #

Concentration Color pH number

1.0 M NaCl

0.10 M NaCl

0.010 M NaCl

0.0010 M NaCl

0.00010 M NaCl

0.000010 M NaCl

0.0000010 M NaCl

0.00000010 M NaCl

0.000000010 M NaCl

Making Sense

• What does concentration have to do with the acidity or basicity of a solution?

More H+ More OH–

pH scale

(cont.)

Arrhenius definition:

• An acid is any substance that adds a hydrogen ion (H+) to the solution.

• A base is any substance that adds a hydroxide ion (OH–) to the solution.

(cont.)

HA H+ + A–

XOH X+ + OH–

(cont.)

Check-In

• Lemon juice has a pH of about 2. What does this tell you about what is in the solution?

• What would happen if you diluted this solution?

Wrap-Up

• The acidity and basicity of a solution are related to the concentration of the solution. Dilute solutions are less acidic and basic than more concentrated solutions.

• Dilution of an acid or a base results in a solution that is increasingly neutral.

(cont.)

• The pH scale is related to the concentration of H+ and OH– ions in solution.

• According to Arrhenius, an acid is any substance that adds a hydrogen ion (H+) to the solution and a base is any substance that adds a hydroxide ion (OH–) to the solution.

Lesson 3:

pHooey!

ChemCatalyst

Examine the following data:

Substance pH

0.10 M HCl 1.0

0.010 M HCl 2.0

0.0010 M HCl 3.0

1.0 M NaOH 14.0

0.10 M NaOH 13.0

0.010 M NaOH 12.0

Water 7.0 (cont.)

• What do you think pH really represents?

• How does the concentration of the solutions relate mathematically to the pH of the solutions?

(cont.)

The Big Question

• How does pH relate to the concentrations of acidic and basic solutions?

Find the pH of a solution if you know the concentrations of hydrogen or hydroxide ions that it contains.

Activity

Purpose: You will explore the relationship between pH, pOH, [H+], and [OH–].

(cont.)

Substance Acidic or

Basic?

pH [H+] (in decimal)

[H+] (in scientific

notation)

1 M HCl

Stomach acid (0.1 M HCl) Acidic 0.1 M 1.0 10–1 M

Clear Soda 3 0.001 M

Rain Water Acidic 1.0 10–6 M

Distilled Water 7 0.0000001M

Alcohol Neutral

Salt Water 0.0000001 M

Washing Soda Basic 8 1.0 10–8 M

Ammonia 0.0000000001 M 1.0 10–10 M

Drain Cleaner (0.1 M NaOH)

1 M NaOH 1.0 10-14 M

Well pH [H+] [OH–] pOH

A 1 1.0 10–1 M 13

B 2 1.0 10–2 M 1.0 10–12 M

C 3 1.0 10–3 M

D 4 1.0 10-4 M 1.0 10–10 M

E 5 1.0 10–5 M

F 6 1.0 10–6 M

G 7 1.0 10–7 M

H 7 1.0 10–7 M 1.0 10–7 M 7

I 7 1.0 10–7 M 7

Well pH [H+] [OH–] pOH

R 7 1.0 10–7 M 1.0 10–7 M 7

Q 7 1.0 10–7 M 7

P 7 1.0 10–7 M

O 8 1.0 10–8 M

N 9 1.0 10–9 M 1.0 10–5 M 5

M 10 1.0 x10–10 M

L 11 1.0 10–11 M

K 12 1.0 10–12

M1.0 10–2 M

J 13 1.0 10–13 M

1.0 10–1 M 1

Making Sense

• How are pH and pOH related to each other mathematically?

This box would show 1,000 H+ ions and 1,000 Cl– ions.

This box would show 100 H+ ions and 100 Cl– ions.

Key: H+ Cl–

pH = 4

pH = 5 pH = 6 pH = 7

(cont.)

pH = –log[H+]

pOH = –log[OH–]

(cont.)

Sample Problem:

• What is the pH of a solution with a hydrogen ion concentration of 3.4 10–4 moles/ L?

(cont.)

Please be careful when entering scientific notation into your calculator—it is very easy to make a mistake. When entering 3.4 10–4, first enter “3.4”. Then press the button labeled “EXP” or “10X” or “EE”. Now enter –4, using the “+/–“ key, not the subtraction key. Never try to enter this number by pressing “X” and “10” and “–4”.

(cont.)

Check-In

• What is the pH of a solution with [OH–] = 1.0 10–12 M?

Wrap-Up

• The relationship between pH and pOH of a solution is expressed by the following: pH + pOH = 14.

• The relationship between [H+] and [OH–] in a solution is expressed by the following: –log [H+] + –log [OH–] = 14.

• The pH of a solution is logarithmically related to the concentration of hydrogen ion and can be calculated mathematically using the following equation: pH = log [H+]

Lesson 4:

Proton Shuffle

ChemCatalyst

Besides HCl, the digestive system also produces a compound called bicarbonate, HCO3

–. Bicarbonate plays a vital role in regulating the pH of the digestive system.

• Do you think bicarbonate, HCO3–, is an

acidic, basic or neutral substance? Explain your reasoning.

The Big Question

• Is there a better way to classify acids, bases, and neutral substances?

Explain the behavior of acids and bases on a molecular level.

Activity

Purpose: This activity will provide you with information to expand on your definition of acids and bases.

(cont.)

Making Sense

• The Arrhenius definition of acids and bases defines them as substances that release either H+ or OH–. How can we expand on this definition to include substances like methylamine, CH3NH2, and ammonia, NH3?

(cont.)

Neutral Substances(cont.)

Brønsted-Lowry definitions

• An acid is a substance from which a proton can be removed.

• A base is a substance that can remove a proton from another substance.

(cont.)

H2O (l) H+(aq) + OH–

(cont.)

NH3 (aq) + H2O (l) NH4+ (aq) + OH– (aq)

(base) (acid)

HNO3 H+ + NO3–

HNO3 + H2O H3O+ + NO3–

(acid) (base)

pH = –log[H3O+]

(cont.)

Check-In

• Do you predict a solution of CH4 to be acidic, basic or neutral? Explain.

Wrap-Up

• A Brønsted-Lowry acid is a substance from which a proton can be removed.

• A Brønsted-Lowry base is a substance that removes a proton from an acid.

• When an acid reacts with water, hydronium ion is produced.

• Some substances can act as both acid and base.

Lesson 5:

Neutral Territory

ChemCatalyst

Milk of magnesia, Mg(OH)2, can reduce excess stomach acid, HCl.

• What products do you think are produced when Mg(OH)2 and HCl are mixed?

• What do you think happens when you add an acid together with a base?

The Big Question

• How do acids and bases interact with each other?

Write balanced chemical equations describing the interactions between acids and bases.

Activity

Purpose: In this activity, you will examine the products of reactions between acids and bases.

(cont.)

starting solution

pH at start

solution added

pH after mixing

acidic, basic, or neutral

Did a reaction occur?

Reactions with NaOH

0.10 M HCl 0.10 M NaOH

0.10 M HNO3

0.10 M NaOH

solid Ca(OH)2

0.10 M NaOH

Reactions with HCl

0.10 M NaOH

0.10 M HCl

0.10 M HNO3

0.10 M HCl

solid Ca(OH)2

0.10 M HCl

Making Sense

Complete the following set of general equations for the reaction of HCl and NaOH with the “generic” acid HA and the “generic” base MOH.

HA + HCl HA + NaOH MOH + HCl MOH + NaOH

• A neutralization reaction is a reaction in which an acid and a base react in aqueous solution to produce a salt and water.

(cont.)

HA + MOH MA + H2O

(cont.)

2HCl (aq) + Mg(OH)2

MgCl2 (aq) + 2 H2O (l)

(cont.)

Check-In

• Sulfuric acid, H2SO4, reacts with magnesium hydroxide, Mg(OH)2. Write a balanced equation for the reaction that occurs.

Wrap-Up

• A neutralization reaction is a reaction between an acid and a base to produce a salt and water.

• When acids are mixed with acids, the pH remains less than 7. When bases are mixed with bases, the pH remains greater than 7.

Lesson 6:

Drip Drop

ChemCatalyst A student mixes 100 mL of 0.10 M HCl with

different volumes of 0.10 M NaOH.

A. 100 mL of 0.1 M HCl + 50 mL of 0.1 M NaOH

B. 100 mL of 0.1 M HCl + 100 mL of 0.1 M NaOH

C. 100 mL of 0.1 M HCl + 150 mL of 0.1 M NaOH

(cont.)

• Which solution is the least toxic?

• Are the final solutions acid, basic, or neutral?

(cont.)

The Big Question

• How can the interactions of acids and bases be used to determine the concentration of a particular acidic or basic solution?

Use the experimental method known as “titration” to determine the unknown concentration of an acid or base.

Activity

Purpose: This activity will introduce you to a laboratory procedure used to determine the concentration of an acid or a base.

(cont.)

HCl solution Drops of 0.10 M NaOH added to neutralize

Calculated concentratio

n of HCl

20 drops HCl Solution A

20 drops HCl Solution B

20 drops HCl Solution C

(cont.)

Initial volume of HCl

Volume of 0.10 M

NaOH added

Total moles of NaOH

Total moles of

Initial HCl concentra

1.0 L 1.0 L 0.10 moles

0.10 moles

0.10 M

100 mL 200 mL 0.020 moles

0.020 moles

50 mL 200 mL

0.0025 moles

0.050 M

100 mL 73 mL

Making Sense

• Describe how you determined the concentration of the NaOH solution in Problem 6.

• A titration is a method for determining the concentration of an acid or base solution by reacting a known volume of the solution with a solution of known concentration. When the moles of H+ are equal to the moles of OH– in the solution, the reaction has reached the equivalence point of the titration, sometimes referred to as the endpoint.

(cont.)

Example:

• If 25.00 mL of 0.50 M nitric acid, HNO3, solution are required to titrate 62.00 mL of sodium hydroxide, NaOH, what is the molarity of the NaOH?

(cont.)

Check-In

You place 50 drops of HCl in a beaker along with a drop of phenolphthalein indicator. After you have added 100 drops of 0.10 M NaOH, the color is a very faint pink.

• What is the concentration of the HCl solution?

Wrap-Up

• A titration is a procedure that allows you to calculate the concentration of an unknown acid or base using a neutralization reaction.

• During a titration, when the moles of H+ are equal to the moles of OH– in the solution, the reaction has reached the equivalence point of the titration, sometimes referred to as the endpoint.

Lesson 7:

Call Poison Control

ChemCatalyst

Imagine that your little brother spilled a toxic substance on his skin. You decide to call Poison Control: 1 (800) 222–1222.

• What are some things that you might want to know about the substance?

• What kinds of questions do you think Poison Control will ask you? What might they tell you to do? Explain your thinking.

The Big Question

• How do solubility and pH contribute to the toxicity of a substance?

Use the mole concept and balanced chemical equations to calculate the mass relationships between products and reactants and determine the concentrations or pH of solutions in which the reactions are a part.

Activity

Purpose: The purpose of this worksheet is to review some of the key ideas in the Toxins Unit.

Making Sense

• No Making Sense exercises.

Check-In

• No Check-In exercise.

Wrap-Up

• No Wrap-Up points.

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