Unit 5

Molar mass and moles

100

The mass in grams of one mole of a substance?

Molar mass

200

C₃H_{8 +} 5O₂ -> 3CO₂ + 4H₂O

Mole ratio of O₂ and H₂O

5/4

300

Molar mass of H₂O?

18g

400

How many atoms in a mole?

6.022 x 10²³

500

What is the mass of 2.5 moles of O2?

2.5 x 32 = 80g

Stoichiometry

100

3.18 x 10⁵ =?

7.94 x 10^-3 =?

318,000

0.00794

200

Which contains more atoms: 1 mol C₃H₈, 1 mol H₂SO₄, 1 mol NaCl

C₃H₈

300

List all steps and names.

1. gram->mol

2. mol->mol

3. mol->gram

400

5C + 2SO₂ -> CS₂ + 4CO

How many moles SO₂ are required to make 118 mol CS₂?

 

236 mol SO₂

500

2Mg+ O₂ -> 2MgO

How many grams of MgO are produced when 2.37 grams of Mg are reacted with an excess of O₂? Report your answer to two decimal places.

2.37 g  / 24.305 g = 0.0975 mol Mg

0.0975 mol Mg x 2 mol MgO / 1 mol Mg = 0.0975 mol MgO

0.0975 mol x 40. 3044 g = 3.93 g MgO

Limiting Reagent and Percent Yield

100

The measured/actual yield will always be smaller or bigger?

Smaller

200

The substance that runs out first in a reaction?

Limiting reagent

300

Measure of a chemical reaction's efficiency?

Percent yield

400

How to calculate the percent yield?

actual(measured)/theoretical x 100%

500

Heating an ore of antimony (Sb₂S₃) in the presence of iron gives the element antimony and iron(II) sulfide.

Sb₂S₃+ 3Fe -> 2Sb + 3FeS 

When 15.0 g Sb₂S₃ reacts with an excess of Fe, 9.84 g Sb is produced. What is the percent yield of this reaction?

15.0 g / 339.715 g = 0.04415 mol Sb₂S₃

0.04415 mol Sb₂S₃ x 2 mol Sb = 0.0883 mol Sb

0.0883 mol Sb x 121.76 g = 10.75 g Sb

9.84  / 10.75 x 100% = 91.5%

Calculations

100

How many atoms are in C₆H₁₂O₆

24 atoms

200

2Ga + 3Br₂ -> 2GaBr₃

How many grams of GaBr₃ are produced when 113 grams of Br₂ are reacted with an excess of Ga? Report your answer to the nearest whole number.

 Ga: 69.72 g/mol

 Br₂: 159.80 g/mol

 GaBr₃: 309.42 g/mol

1. 113/159.80 = 0.7071 mol Br₂

2. 0.7071*2/3 = 0.4714 mol GaBr₃

3. 0.4714 * 309.42 = 146 g GaBr₃

300

When 84.8 grams of iron(III) oxide reacts with an excess of carbon monoxide, 54.3 grams of iron are produced. 

Fe₂O₃ + 3CO -> 2Fe + 3CO₂

What is the percent yield of this reaction?

84.8 g / 159.69 g = 0.5310 mol Fe₂O₃

0.5310 mol Fe₂O₃ x 2 mol Fe = 1.062 mol Fe

1.062 mol Fe x 55.845 g Fe = 59.3 g Fe

54.3 / 59.3 x 100% = 91.6%

400

A 2.80 g sample of Al reacts with a 4.15 g sample of Cl₂ according to the equation shown below.

2Al(s) + 3Cl₂(g) -> 2AlCl₃(s)

What is the theoretical yield of AlCl₃ in this reaction?

- 2.80 g / 26.98 g = 0.104 mol Al

- 4.15 g / 70.90 g = 0.0585 mol Cl₂

- 0.104 mol Al x 2 mol AlCl₃ / 2 mol Al = 0.104 mol AlCl₃

- 0.0585 mol Cl₂ x 2 mol AlCl₃ / 3 mol Cl₂ = 0.039 mol AlCl₃

- 0.039 mol x 133.33 g = 5.20 g AlCl₃

500

A tin crocodile is composed of 6.85 x 10²⁴ atoms of tin. What is the mass of the tin crocodile in grams? Report your answer to the nearest whole number.

1. 6.85 x 10²⁴ / 6.022 x 10²³ = 11.375 mol

2. 11.375 x 118.71= 1350 g