Sc 126 stoichiometry worksheet week 6

SC156 Unit 6 Stoichiometry Assignment

TOTAL 90 PTS

Part 1. (Total 42 points for Part 1)

Imagine that you are a forensic chemist investigating a murder involving an alleged poisoning. The victim was poisoned with a compound called dichlorobenzene (C6H4Cl2). The autopsy results show that the victim’s body contained about 31 grams of the poison, but the actual amount could have been higher since some of it could have been absorbed in the victim’s tissue. Katherine, the victim’s wife, is the main suspect and works as a chemistry professor at the local community college. Records show that she purchased 15 grams of benzene (C6H6) two days before the murder. Benzene is a chemical used to make the poison, but Katherine claims she was using it to make methyl benzene (C6H5CH3), a harmless compound she needed for her lab. She shows you the bottle of methyl benzene she claims to have made. It contains 25 grams of methyl benzene.

Is she telling the truth or did she poison her husband? Work through the problems below to find out.

1. Balance the chemical equations below. (2 PTS) The first equation represents the reaction to produce dichlorobenzene. The second equation represents the reaction to produce methyl benzene.

a. Cl2 + C6H6 —-> C6H4Cl2 + H2

b. CH4 + C6H6 —-> C6H5CH3 + H2

2. Calculate the molar mass of methyl benzene. Show your work. (3 PTS: 1 PT correct answer +

2 PTS work)

3. Calculate the molar mass of benzene. Show your work. (3 PTS: 1 PT correct answer + 2 PTS

work)

4. Using the equations above and the molar masses you calculated, how many grams of methyl benzene can be produced from 15 grams of benzene? Show all of your work. (15 PTS: 5 PTS for ans + 10 PTS for work)

5. Based on the amount of methyl benzene that you calculated in number 4 above, is it possible to produce 25 grams of methyl benzene from 15 grams of benzene? Was Katherine telling the truth or did she poison her husband? Why or why not? (4 PTS)

6. How many grams of benzene would be needed to produce 31 grams of dichlorobenzene?

(15 PTS: 5 PTS for ans + 10 PTS for work)

Part 2. (Total 48 points for Part 2)

Imagine that you are the newest employee of the Cookie Factory. The cookie baker whose position you filled was also a chemist and left under bad circumstances. Upset that he was not granted a percentage of the cookie factory, he abruptly quit and changed his signature chocolate chip recipe from standard cooking measurements to moles so that no one could reproduce his recipe. You will have to convert his chocolate chip cookie recipe from moles to

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standard cooking measurements in order to bake your first batch of cookies. Begin by converting moles to grams for each ingredient in the recipe and record the grams in the provided table. Next, convert the number of grams to your final baking measurement and record your data in the provided table.

Make sure you show all of the work used to complete your calculations in order to receive full credit for your work.

1. Use the molecular formulas below to calculate grams of ingredients. Take note that the molecular formulas listed are representative formulas only, since most of these ingredients have very complex molecular formulas.

(3 PTS total per each answer: 1 PT for correct ans + 2 PTS for work)

Ingredient

White (Cane) Sugar Baking soda

Flour

Butter

Eggs

Vanilla

Brown sugar Chocolate chips

Representative Molecular Formula C12H22O11 NaHCO3

C4H8O4 C9H14O6 C6H12O3N2 C8H8O3 C12H22O11 C4H8O4

2. Use the conversion factors below to convert from grams to a standard cooking unit measurement.

(3 PTS total per each answer: 1 PT for correct ans + 2 PTS for work)

1 teaspoon of baking soda = 2.84 grams

1 teaspoon of vanilla extract = 4.73 grams 1 large egg = 50 grams

1 cup flour = 141.95 grams

1 cup butter = 236.59 grams

1 cup white sugar = 198.73 grams

1 cup brown sugar = 141.46 grams

1 ounce chocolate chips = 28.35 grams

3. Below is the secret chocolate chip cookie recipe. You will need to convert moles to grams for each ingredient and record the grams in the provided table. Then convert the number of grams to your final baking measurement.

(Be sure to use this recipe info!)

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Ingredients:

2.66 moles flour

0.44 moles white sugar

0.31 moles packed brown sugar 0.624 moles eggs

Baking Instructions:

Chocolate Chip Cookies

0.0335 moles baking soda 1.084 moles butter

0.062 moles vanilla

2.82 moles chocolate chips

Preheat oven to 375 °F. Stir flour with baking soda; set aside. In larger bowl, cream butter with white sugar, brown sugar, eggs and vanilla. Gradually blend the flour mixture into creamed mixture. Stir in the chocolate chips. Drop one tablespoon of dough per cookie onto ungreased cookie sheet. Bake at 375 °F for 9 to 11 minutes or until golden brown.

Record your data for Part 2 of this assignment in the table below.

Ingredient

Flour

Baking soda Butter

White Sugar Brown Sugar Eggs

Vanilla Chocolate chips

Grams

Baking Measurements

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