Hoang Unit 4 Test Review 3

Determine the empirical formula of a compound that is 40% sulfur and 60% oxygen by mass.

Answer explanation

To find the empirical formula, convert the percentages to moles: 40g S (1 mol S = 32g) = 1.25 mol S; 60g O (1 mol O = 16g) = 3.75 mol O. The ratio is 1:3, simplifying to SO2, which matches the correct answer.

Tags

NGSS.HS-PS1-7

Answer explanation

The empirical formula CH₂ has a molar mass of 14 g/mol (C: 12 + H: 2). To find the molecular formula, divide the molar mass (56 g/mol) by the empirical formula mass (14 g/mol) to get 4. Thus, the molecular formula is C₄H₈.

• 1 mole

• 2 moles

• 4 moles

• 8 moles

Answer explanation

The reaction shows that 2 moles of H2 produce 2 moles of H2O. Starting with 4 moles of H2 means you can produce 4 moles of H2O, as the ratio is 1:1. Thus, the correct answer is 4 moles.

Tags

NGSS.HS-PS1-7

If a compound is composed of 70% iron and 30% oxygen by mass, what is its empirical formula? (Atomic masses: Fe = 56, O = 16)

Answer explanation

To find the empirical formula, convert mass percentages to moles: 70g Fe (70/56 = 1.25 mol) and 30g O (30/16 = 1.875 mol). The ratio of Fe to O is 1.25:1.875, simplifying to 3:4. Thus, the empirical formula is Fe_3O_4.

Tags

NGSS.HS-PS1-7

Answer explanation

To find the empirical formula, divide the subscripts in the molecular formula C6H12O6 by their greatest common divisor, which is 6. This gives CH2O, the simplest whole number ratio of the elements.

Answer explanation

The empirical formula NH₂ has a molar mass of 16 g/mol. To find the molecular formula, divide the molar mass (32 g/mol) by the empirical formula mass (16 g/mol), yielding 2. Thus, the molecular formula is N₂H₄.

A compound is found to contain 85.7% carbon and 14.3% hydrogen by mass. What is the empirical formula of the compound? (Atomic masses: C = 12, H = 1)

Answer explanation

To find the empirical formula, convert the percentages to grams (85.7g C, 14.3g H). Calculate moles: C = 85.7/12 = 7.14, H = 14.3/1 = 14.3. Divide by the smallest number of moles (7.14): C = 1, H = 2. This gives CH_2. However, the ratio simplifies to CH_3.

• 1 mole

• 2 moles

• 3 moles

• 4 moles

Answer explanation

From the reaction, 3 moles of A produce 1 mole of C. With 9 moles of A, we can produce 3 moles of C (9 moles A / 3 moles A per mole C). 6 moles of B can also support this reaction (2 moles B per mole C). Thus, 3 moles of C are produced.

Tags

NGSS.HS-PS1-7

What is the empirical formula if you have 88.80% copper and 11.20% oxygen?

• Cu₃O₈
• CuO₄
• Cu₂O
• Cu₄O₁₀

The mass of one mole of substance is called...

• molecular mass
• mole constant
• molar mass
• atomic weight