Question

Stichiometry Project

B. S’mores:

You have one bag of marshmallows. What is the maximum number of s’mores that can be made? How many boxes of graham crackers and how many chocolate bars are needed to make this many s’mores?

a. Write a balanced chemical equation using the symbols in the table below.

Substance	Symbol	Unit Mass
Graham Cracker	Gc	7.00 g/cracker
Marshmallow	Mm	7.09 g/marshmallow
Chocolate Piece	Cp	3.30 g/piece
S’more	Gc2MmCp3	__________ g/s’more

b. Calculate the unit mass of the s’more (Gc2MmCp3).

c. If there are 454 g of marshmallows in one bag, how many marshmallows do you have?

d. The coefficients in a balanced reaction give you the ratios between all of the products and reactants. Use these ratios to relate the number of marshmallows you have to the number of graham crackers and chocolate segments needed.

i. Ratio of Mm : Gc  is ________; # of graham crackers needed is _______

ii. Ratio of Mm : Cp is _________; # of chocolate pieces needed is _________

e. Using the unit mass values, determine the total mass of graham crackers and chocolate pieces that are needed. If a box of graham crackers has a mass of 254 grams, how many boxes do you need? If one chocolate bar has a mass of 49.5 grams, how many bars do you need? (Remember that you will be purchasing whole boxes and bars.)

f. How many s’mores can be made from 100. g of each ingredient?  What is your limiting reagent?

3. When a piece of aluminum metal is dropped into hydrochloric acid, HCl, hydrogen is released as a gas and a solution of aluminum chloride forms. Write a balanced equation for this reaction. How many grams of aluminum are needed to make 5.50 grams of aluminum chloride? How many grams of hydrogen gas are given off during this reaction?

Answer 1

a. The balanced chemical equation using the symbols in the table

2 Gc + 1 Mm + 3 Cp -------> Gc2MmCp3

b. Calculate the unit mass of the s’more (Gc2MmCp3).

2 (7.00 ) + 1(7.09) +3 (3.30) = 30.99 g/s’more

c)

Unit Mass of marshmallow = 7.09 g

So, in 454 g of marshmallows there are 454 g/7.09 g = 64 marshmallows

One bag, contains 64 marshmallows

d. The coefficients in a balanced reaction give you the ratios between all of the products and reactants. Use these ratios to relate the number of marshmallows you have to the number of graham crackers and chocolate segments needed.

i. Ratio of Mm: Gc is 1:2 # of graham crackers needed is 64 x 2 = 128

ii. Ratio of Mm: Cp is 1:3 # of chocolate pieces needed is 64 x 3 = 192

e)

The total mass of graham crackers = Unit Mass of graham cracker x # of graham crackers

The total mass of graham crackers = 7.00 g x 128 = 896 g

A box of graham crackers has a mass of 254 grams

So, 896 g graham crackers need 896 g/254 g = 3.52 = 4

896 g graham crackers need 4 boxes

The total mass of chocolate = Unit Mass of chocolate x # of chocolate pieces

The total mass of chocolate = 3.30 g x 192 = 663.6 g

If one chocolate bar has a mass of 49.5 grams

So, 663.6 g chocolate have 663.6g/49.5 g = 13.4 = 14 bar

663.6 g chocolate need 14 bars

f. How many s’mores can be made from 100. g of each ingredient

Calculate the mass unit each ingredient

100g/7.00 g/cracker = 14.29 cracker

100 g/7.09 g/marshmallow = 14.10 marshmallow

100g/3.30 g/piece chocolate =30.30 piece chocolate

Ratio of Mm: Gc : cp = 1:2:3

2 Graham crackers react with 1 marshmallow

14.29 crackers react with 14/2 = 7 marshmallow

Graham crackers limiting reagent

2 Unit Mass of graham cracker form 1 s’more

14 graham crackers form 14/2 = 7 s’more

3.

2Al(s)+6HCl(aq) ----->3H₂(g)+2AlCl₃(aq)

2(26.98) + 6(36.46) ----> 3(2) + 2(133.34 )

53.96 + 218.76 -----> 6 + 266.68

266.68g of aluminum chloride is produced from 53.96 g of aluminum

5.50 grams of aluminum chloride is produced from 5.50 x (53.96 g /266.68g) of aluminum

1.11 grams of aluminum are needed to make 5.50 grams of aluminum chloride

53.96 grams of aluminum gives 6 g of H₂

1.11 grams of aluminum gives = 1.11g x 6g /53.96g = 0.123 g

0.123 grams of hydrogen gas are given off during this reaction