ECA Review

Calculate the number of moles in 2.46 × 10²¹ molecules of CO₂.

• 1.66 × 10⁻²⁰
• 4.09 × 10⁻³
• 2.00 × 10⁴
• 1.45 × 10⁹

Calculate the molar mass of (NH₄)₂C₂O₄. .

• 100.00 g/mol
• 124.10 g/mol
• 240.78 g/mol
• 316.20 g/mol

A gaseous hydrocarbon has a density of 2.59 g/L at STP. What is the identity of the hydrocarbon?

• Butane, C₄H₁₀
• Ethane, C₂H₆
• Methane, CH₄
• Propane, C₃H₈

What is the percent composition of PbO₂?

• 50% Pb, 50% O₂
• 86.6% Pb, 13.4% O₂
• 43.4% Pb, 56.6% O₂
• 33.3% Pb, 66.7% O₂

A compound is analyzed and found to have the percent composition shown in the pie chart. What is the empirical formula for this compound?

• Na₂S₂O₃
• Na₂S₃O₂
• Na₁SO₄
• Na₂SO₂

What is the molarity when 4.24 mol of NaCl is prepared in 2.00 L of solution?

• 1.06 M
• 2.12 M
• 4.24 M
• 8.48 M

What is the molarity of a solution that contains 78.5 g of copper(II) chloride in 1.50 L of solution?

• 52.3 M
• 0.390 M
• 1.14 M
• 0.585 M

What is the density of carbon monoxide gas at STP conditions?

• 0.800 g/L
• 1.25 g/L
• 22.4 g/L
• 28.0 g/L

It states that every sample of the same substance contains identical elements in the same fixed ratio by mass.

• Avogadro's Law
• Law of Conservation of Mass
• Law of Definite Proportion
• Boyle's Law

A lab technician knows the empirical formula of a molecule is CH₂. He uses a mass spectrometer to determine the molar mass of the compound. The test results show that the molar mass is 56.1 g/mol. What is its molecular formula?

• CH₂
• C₂H₄
• C₃H₆
• C₄H₈