CHEM 121 Exam 1

Properties & Classifications

100

Classify distilled water as an element, compound, or mixture.

Compound

200

Classify the following as a chemical or physical process: Mothballs vaporize in a cedar chest.

Physical

300

Classify the following reaction by type: 

2C₂H₂(g)+5O₂(g)→4CO₂(g)+2H₂O(g)

Combustion

400

Identify if measuring the mass of a solid formed in a reaction is an intensive or extensive property

Extensive

500

Determine if the ratio of mass to volume (density) for a metal sample is an intensive or extensive property.

Intensive

Nomenclature & Formulas

100

Provide the chemical formula for Sodium sulfate

Na₂SO₄

200

Write the formula unit for the compound formed by Magnesium and the Phosphate ion.

Mg₃(PO₄)₂

300

Name the binary molecular compound represented by the formula P₂O₅.

Diphosphorus pentoxide

400

Determine the empirical formula for a compound containing 49.5% C,5.15% H,28.9% N and 16.5% O

.

C₄H₅N₂O

500

Based on the empirical formula above and a molar mass of 195 g/mol, find the molecular formula for Caffeine.

C₈H₁₀N₄O₂

Unit Conversions & Density

100

Determine the number of significant figures in the result of: 

(29.4-20.4) / 3.00

2 significant figures

200

Convert a temperature of 101.5∘F into Kelvins.

311.8K

300

A container has a volume of  5.20×10^-4 m³. Calculate the volume in cm³

.

520 cm³

400

Solve for the mass in grams of a metal sample if its density is 7.87 g/cm and its volume is 15.0 cm³

118g

500

Benzene has a density of 0.879 g/mL. Calculate the volume in liters of 637 g of benzene.

0.725 L

Atoms, Isotopes & Moles

100

Calculate the number of neutrons in a single atom of silver-108 (Atomic # 47)

61

200

Calculate the number of moles of oxygen atoms present in 4.86 mol of CaCO_3.

14.58 mol

300

Determine the percent composition by mass of Carbon in Propane (C₃H₈).

81.7%

400

A compound contains 49.5% C, 5.15% H, 28.9% N, and 16.5% O. Calculate its empirical formula.

C₄H₅N₂O

500

Calculate the average atomic mass of Gallium: 60.11% Ga (68.9256 amu) and 39.89% Ga (70.9247 amu)

69.72 amu

Stoichiometry & Yields

100

Provide the sum of the coefficients for the balanced equation: 

CH₃OH + O₂ -> CO₂ + H₂0

2+3+2+4 = 11

200

Calculate the molar mass of Caffeine (C₈H₁₀N₄O₂)

194.19 g/mol

300

If 14.2 g of Al₂S₃ reacts with 65.8 g of H₂O, identify the limiting reactant.

Al₂S₃

400

14.2 g of Al₂S₃ reacts with 65.8 g of H₂O

Based on the limiting reactant above, calculate the theoretical yield of Al(OH)₃ in grams.

14.7 g

500

If 10.0 g of benzene (C₆H₆) reacts with bromine (Br) to produce 42.3 g of bromobenzene (C₆H₅Br), what is the percent yield?

54.2%