1. A molecule is found to contain 47.35% by mass C, 10.60% by mass H, and 42.05% by mass O. What is the empirical formula for this molecule?

C3H8O2

2.Which element is most likely to form a 2– ion?

K, S, Mg, P, Br

S

3. You have 6.23 moles of each of the following elements: Li, Ca, Fe, S and Cu. Which sample contains the largest mass in grams?

Cu

4. How many hydrogen atoms are present in 1.89 g of NH₃?

2.00E+23

5. How many protons, neutrons, and electrons are in a silver atom with a mass number of 108?

47 P

61 N

47 E

6. Which one of the following substances is classified as an element?

C6H12O6, I2, NO, CO, KCl

I2

7. The density of ice at 0 °C is 0.917 g/mL. What is the volume of 322 g of ice?

351mL

8. What is the percent yield if 15.5 g SF₆ is isolated from the reaction of 14.5 g S₈ and 58.6 g F₂?

S8(s) + 24 F2(g) → 8 SF6(g)

23.5%

9. Which of the following observations is/are examples of chemical change?
1.Iron (Fe) rusts, forming Fe₂O₃.

2.The density of water increases when it changes from a solid to a liquid.

3.Sodium chloride melts at 801 °C

1 only

10. Two electronic balances are tested using a standard weight. The true mass of the standard is 5.0000 g. The results of 5 individual measurements on each balance are recorded below.

A: 5.2895, 5.1077, 4.6407, 4.8947, 5.0672

B: 5.0001, 4.9998, 4.9999, 5.0002, 4.9999
Which statement best describes the results?

A: poor precision and good accuracy

B: good precision and accuracy

11. How many protons, neutrons and electrons are present in one ion of ³¹P^3–?

protons = 15, neutrons = 16, electrons = 18

12. How many moles of sodium bromide can be produced from the reaction of 5.82 moles of sodium with 3.04 moles of bromine gas?

2 Na(s) + Br₂(g) → 2 NaBr(s)

5.82 mol

13. Aluminum reacts with hydrochloric acid to produce aluminum chloride and hydrogen gas.

2 Al(s) + 6 HCl(aq) → 2 AlCl₃(aq) + 3 H₂(g)

What mass of H₂(g) is produced from the reaction of 0.743 g Al(s) with excess hydrochloric acid?

8.34E-2 g

14. Which of the following compounds are named correctly?

1. BaI₂, barium(I) iodide
2. CoO, cobalt(II) oxide
3. FeBr₃, iron(II) bromide

2 only

15. Write the balanced chemical equation for the reaction below and indicate the smallest whole number coefficient for each substance.

__iron(III) carbonate(s) + __hydrochloric acid(aq) __iron(III) chloride + __H₂O(l) + __CO₂(g)

1 6 2 3 3

16. Calculate the number of moles of aluminum oxide in 8.25 g Al₂O₃.

8.09E-2 mol

17. Rubidium has two naturally occurring isotopes. The average mass of Rb is 85.4678 u. If 72.15% of Rb is found as Rb-85 (84.9117 u), what is the mass of the other isotope?

86.91u

18. Which of the following is the smallest mass?

2.12e-5g

1.74e+7ng

2.52e+9pg

0.154mg

2.71e+6ng

2.12e-5g

19. Round 0.00763521 to 3 significant figures.

0.00764

20. Which of the following compounds are named correctly?

1. NO₂, nitrogen oxide
2. PCl₅, phosphorous pentachloride
3. NH₄I, ammonium monoiodide

2 & 3

21. What is the correct answer to the following expression: (201.83 – 146.00) ÷ 7.109?

7.853

22. Identify the ions present in Na₂SO₄.

Na⁺ and SO₄ ^2–

23. Which two of the atoms below have the same number of neutrons?
(mass/atomic number)

S34/16

S32/16

Cl35/17

Ar38/18

S34/16 and Cl35/17

24. What is the percent by weight of hydrogen in propane, C₃H₈?

18.32

25. How many grams of fluorine are present in 3.56 moles of boron trifluoride?

203