Part II. Multiple choice, continued (3 points each). Name:__________________ Please circle your answer. There is only one correct answer to each question. 5. Which of the following molecular formulas is also an empirical formula? A) C6H6O2 B) C2H6SO C) H2O2 D) C6H6 6. What is the coefficient of O2 when the following equation is completed and balanced? C4H8O2 + O2 à ______________ A) 2 B) 3 C) 5 D) 6 7. Analysis of a compound shows that it contains 3.75 moles of C, 7.50 moles of H, and 1.25 moles of N. What is its empirical formula? A) CHN B) C3H6N C) C4H8N D) C5H9N2 8. What is the molar mass of Ca(NO3)2? (AW Ca = 40.1 amu; N = 14.0 amu; O = 16.0 amu) A) 70.1 g/mol B) 62.0 g/mol C) 164.1 g/mol D) 102.1 g/mol 9. Which of the following is an alkali metal? A) Mg B) Fe C) Al D) Na 10. A compound contains 40.0% C, 6.71% H, and 53.29% O by mass. The molecular weight of the compound is 60.05 amu. The molecular formula of this compound is A) C2H4O2 B) CH2O C) C2H3O4 D) C2H2O4 11. How many molecules of water, H2O, are there in 28.0 grams of water? A) 9.37 x 1023 B) 1.56 C) 578 D) 1.56 x 1025 12. When a hydrocarbon burns in air, what component of air reacts? A) nitrogen B) oxygen C) carbon dioxide D) water 13. When the following equation is balanced, the coefficient of Fe3O4 is__________. Al + Fe3O4 à Al2O3 + Fe A) 1 B) 2 C) 3 D) 4

What does the empirical formula represent?

The simplest whole number ratio of atoms in a compound.

How can you determine if a molecular formula is also an empirical formula?

Check if the subscripts can be divided by a common number to get a simpler ratio.

Which molecular formula is already in its simplest form: C6H6O2, C2H6SO, H2O2, or C6H6?

C2H6SO.

What is the balanced equation for C4H8O2 + O2?

C4H8O2 + 5O2 → 4CO2 + 4H2O.

What is the coefficient of O2 in the balanced equation for C4H8O2 + O2 → CO2 + H2O?

5.

How do you determine the empirical formula from mole values?

Divide each mole value by the smallest number of moles present.

What is the empirical formula for C: 3.75 moles, H: 7.50 moles, N: 1.25 moles?

C3H6N.

How do you calculate the molar mass of Ca(NO3)2?

Add the atomic weights of each element multiplied by the number of atoms.

What is the molar mass of Ca(NO3)2?

164.1 g/mol.

Which of the following elements is an alkali metal: Mg, Fe, Al, Na?

Na (Sodium).

How do you find the molecular formula from percent composition?

First find the empirical formula using the percentages, then determine the molecular formula using the molecular weight.

What is the empirical formula if C: 40.0 g, H: 6.71 g, O: 53.29 g?

CH2O.

What do you multiply by to find the molecular formula from the empirical formula CH2O if the ratio is 2?

Multiply the subscripts by 2 to get C2H4O2.

How do you calculate the number of molecules from grams using Avogadro's number?

Calculate the number of moles, then multiply by Avogadro's number.

What is the number of molecules in 28 g of water?

Approximately 9.37 x 10^23 molecules.

Which component of air reacts in combustion?

Oxygen.

What is the balanced equation for Al + Fe3O4?

8Al + 3Fe3O4 → 4Al2O3 + 9Fe.

What is the coefficient of Fe3O4 in the balanced equation Al + Fe3O4?

3.