1. Unit 4: TOXINS Stoichiometry, Solution Chemistry, and Acids and Bases
Living By Chemistry
Unit 4: TOXINS
Stoichiometry, Solution Chemistry, and Acids and Bases

2. In this unit you will learn:
how toxins are defined
how chemists determine toxicity
the mechanisms by which toxic substances act in our bodies and what this has to do with chemical reactions

3. Section II: Weighing Toxins
Lesson 7 Lethal Dose
Lesson 8 Make It Count
Lesson 9 Billions and Billions
Lesson 10 What’s in a Mole?
Lesson 11 Mountains into Molehills
Lesson 12 How Sweet It Is

4. Lesson 7: Lethal Dose
Toxicity

5. ChemCatalyst
Which substance do you think is most toxic to you—alcohol (ethanol, C2H6O), aspirin (salicylic acid, C7H6O3), or arsenic (III) oxide (As2O3)? Explain your thinking.

6. Key Question
How much is too much of a substance?

7. You will be able to:
calculate the toxic dose for a variety of substances, given the LD50
explain the role of dosage in toxicity

8. Prepare for the Classwork
You will work individually or in pairs.
Lethal dose (LD50): the amount of an ingested substance that kills 50% of a test sample of animals. It is expressed in mg/kg, or milligrams of substance per kilogram of body weight.

9. Discussion Notes
Toxicity depends on two quantities: amount of toxic substance and mass of the organism.
All substances are toxic in large enough doses, even sugar and water.

10. Discussion Notes (cont.)
The smaller the lethal dose, or LD50, the more potentially dangerous a substance is.
Many toxic substances can be therapeutic at lower doses.

11. Wrap Up How much is too much of a substance?
Toxicity is relative to dosage: The toxicity (or therapeutic effect) of a substance depends on the dose in which it is received.
The lethal dose (or therapeutic dose) of a substance is often expressed as a ratio between a certain mass of the substance and 1 kilogram of the body mass of an organism exposed to the substance.

12. Check-in
Methadone is a medication used as a painkiller and as a treatment for those recovering from heroin addiction. The LD50 for methadone is 95 mg/kg.
a. Would you consider methadone to be more or less toxic than acetaminophen (LD50 = 2404 mg/kg)? than aspirin (LD50 = 200mg/kg)?
b. Explain how you would calculate the amount of this substance that would be lethal to a 120 lb human.

13. Lesson 8: Make It Count
Counting By Weighing

14. ChemCatalyst The LD50 of arsenic (III) oxide, As2O3, is 15 mg/kg.
Figure out the lethal dose for a 150 lb adult.
How many atoms do you think are in a lethal dose of arsenic (III) As2O3? What would you need to know in order to find out?

15. Key Question
How can mass help you count large numbers of small objects?

16. You will be able to:
explain how large numbers of small objects are determined
calculate the percent error of a calculation

17. Discussion Notes
The easiest way to determine the count of very small objects is to find their total mass and divide by the mass of one object.
In order to get a more accurate average mass measurement for a tiny object, it is better to find the mass of 10 or 20 of the objects and divide by the number of objects to find the average mass, especially if the variation in size is slight.

18. Discussion Notes (cont.)
Chemists use mass when measuring chemical compounds because it is not possible to count atoms directly.

19. Discussion Notes (cont.)
Chemists use percent error to express how close their measurements are to the accepted value.
Percent error = |observed value – actual value| • actual value

20. Discussion Notes (cont.)
Object
Mass (g)
seed bead g
large pony bead
0.26 g
sequin g
#18 medium rubber band
0.27 g
grain of rice
0.022 g
elbow pasta
0.287 g
tiny rubber band
0.048 g
large sticky note
0.40 g
small pony bead
0.067 g
plastic paper clip
0.45 g
split pea
0.090 g
kidney bean
0.55 g
#10 small rubber band
0.126 g
#33 large rubber band
0.57 g
small sticky note
0.15 g
business card
0.80 g
#8 lock washer
0.136 g
small metal paper clip
0.94 g

21. Wrap Up How can mass help you count large numbers of small objects?
It is possible to count large numbers of small objects by weighing them together and dividing by the mass of a single object.
It is more accurate to weigh a large sample of a collection of objects and find their average mass than to rely on weighing a single object.
There are so many atoms in a sample that you cannot count them. Chemists use mass to calculate numbers of atoms.

22. Check-in
You have a sandwich bag containing raisins. It weighs 24.6 g. A sample of ten raisins weighs 0.90 g. The empty bag has a mass of 2.90 g.
How many raisins are in your sandwich bag?

23. Lesson 9: Billions and Billions
Avogadro’s Number

24. ChemCatalyst
Which do you think is more toxic, 1 mol of arsenic, As, or 10 g of arsenic? Explain your reasoning.

25. Key Question
What is the relationship between mass and moles?

26. You will be able to:
translate numbers into scientific notation, and vice versa
explain the magnitude of a mole
define molar mass for an element and find its value on the periodic table

27. Prepare for the Classwork
Work individually or in pairs.
1 mole ≈ 602,000,000,000,000,000,000,000, or 602 sextillion

28. Discussion Notes
Scientific notation is a convenient way to write numbers that have lots of zeros, either because they are very large or because they are very small.

29. Discussion Notes (cont.)
A number in standard notation can be converted to scientific notation by writing it as a decimal with one digit to the left of the decimal point times a power of ten.
Move the decimal point four places to the right.
Move the decimal point four places to the left.
1.56 X 104 = 15,600
1.56 X 10–4 =

30. Discussion Notes (cont.)
Very small amounts of a substance contain enormously large numbers of atoms.
The mole is simply a counting unit.
The mass of 1 mol of a substance is called the molar mass.
1 mole = Avogadro’s number
= 602 sextillion
= 602,000,000,000,000,000,000,000
= 6.02 X 1023

31. Wrap Up What is the relationship between mass and moles?
One mole of a substance is equal to 602 sextillion—or 602,000,000,000,000,000,000,000 —objects. This is also called Avogadro’s number.
Scientific notation is a convenient way to express numbers that have many zeros.
The atomic mass given on the periodic table is equivalent to the mass of 1 mole of atoms of the element in grams, called molar mass.
Molar mass allows you to convert between moles of atoms and grams of atoms.

32. Check-in
If you have 1 mol of aluminum and 1 mol of iron, which has more mass? How many atoms are in each sample?

33. Lesson 10: What’s in a Mole?
Molar Mass

34. ChemCatalyst
Consider 12 nickels, 2 empty aluminum cans, and a balloon full of carbon dioxide gas.
Which has the greatest mass?
Which has the greatest number of atoms?
Which has the greatest number of moles of atoms? Explain the reasoning behind your answers.

35. Key Question
How can you convert between mass and moles?

36. You will be able to: calculate the molar mass of compounds
describe the approximate magnitude of a mole of a substance
complete simple conversions between mass and moles

37. Discussion Notes
You can figure out the mass of 1 mole of any element or compound using a periodic table.
A mole of atoms or molecules of a solid or a liquid is an amount you usually can hold in your hand.
A mole of any gas, if it is at standard temperature and pressure, always has a volume of 22.4 L.

38. Wrap Up How can you convert between mass and moles?
The molar mass of a compound is the sum of the atomic masses of the atoms in the compound.
The molar mass of a compound allows you to convert between moles of the compound and grams of the compound.

39. Wrap Up (cont.)
One mole of a solid or a liquid is an amount that you usually can hold in your hand.
One mole of a gas occupies a volume of 22.4 L. This is larger than the volume of 1 mol of a liquid or a solid because of the space between gas molecules.

40. Check-in
You have 1 mol of oxygen molecules, O2, and 1 mol of carbon dioxide molecules, CO2. Which has more mass? Which has a larger volume at room temperature?

41. Lesson 11: Mountains into Molehills
Mass-Mole Conversions

42. ChemCatalyst
Arsenic, As, arsenic (III) oxide, As2O3, and arsenic (III) sulfide, As2S3, are all toxic because they contain arsenic.
Which is more toxic, 1 mol of As or 1 mol of As2O3? Explain your thinking.
Which is more toxic, 1 g of As2O3 or 1 g of As2S3? Explain.

43. Key Question
How are moles related to mass?

44. You will be able to:
convert the number of moles of a compound or an element to mass in grams
convert the mass of a sample in grams to moles

45. Discussion Notes
The relationship between mass (g) of a substance and number of moles is proportional.
Mass (g) = k • moles
The proportionality constant, k, is equal to the molar mass of the substance.

46. Discussion Notes (cont.)
The relationship between the number of particles of a substance and the number of moles is also proportional.
Number of particles = k • number of moles
In this case, the proportionality constant, k, is equal to Avogadro’s number, 6.02 X 1023.

47. Wrap Up How are moles related to mass?
In order to convert moles to mass, multiply the number of moles by the molar mass.
In order to convert mass to moles, divide the number of grams by the molar mass.

48. Check-in
A sample of chlorine gas, Cl2, has a mass of 11 g. How many moles of Cl2(g) is this?

49. Lesson 12: How Sweet It Is
Comparing Amounts

50. ChemCatalyst
Consider two cans of carbonated soft drink. One is regular, and the other is diet.
Which do you think is more toxic, the regular soft drink or the diet soft drink? Explain your reasoning
What information would help you answer this question?

51. Key Question
How can you use moles to compare toxicity?

52. You will be able to:
use moles and molar mass to compare the amounts of different substances
discuss the safety of sweeteners

53. Prepare for the Demonstration
Work individually.

54. Discussion Notes
Aspartame molecules are much sweeter than fructose molecules.
The safety of artificial sweeteners has been a subject of debate for years.

55. Discussion Notes (cont.)
It is interesting to compare the LD50 for fructose and for aspartame.
Regular soft drink (fructose)
Diet soft drink (aspartame)
Lethal dose for a 64 kg person
29,7000 mg/kg • 64 kg = 1,900,000 mg = 1,900 g
10,000 mg/kg • 64 kg = 64,000 mg = 64 g
Number of cans
1,900 g/40 g/can ≈ 48 cans
64g / g/can ≈ 280 cans

56. Wrap Up How can you use moles to compare toxicity?
The smaller the LD50, the more toxic a substance is. However, the LD50 values are of limited use in determining the long-term effects of a substance.

57. Check-in
Imagine two substances of equal mass with molecules that are equally toxic.
Would you rather be exposed to the substance with the larger molar mass or the smaller molar mass? Explain your reasoning.