Chemistry Midterm

Chemistry Midterm Review Part 1

Multiple Choice

[3.c]

What is the empirical formula of a compound that has a carbon-to-hydrogen ratio of 2 to 6?

• CH₃

• C₂H₆

• C₃H

Multiple Choice

[3.c]

A compound has the empirical formula CH₂O and a molar mass of 60 ^g/_mol . What is the molecular formula of this compound?

(Hint: Molar mass C = 12 ^g/_mol , Molar mass H = 1 ^g/_mol , Molar mass O = 16 ^g/_mol ) Show your work!

• CH₂O

• C₂H₄O₂

• C₃H₈O

Multiple Choice

[SC3.c]

You work for CSI and have to identify an unknown compound. The analyzer machine tells you it is 22% sulfur (molar mass 32 ^g/_mol) and 78% fluorine (molar mass 19 ^g/_mol). What should you testify in court that the empirical formula of the compound is? ( Hint: ASSUME 100 g TOTAL compound and find the mole ratio of fluorine to sulfur.)

• SF

• SF₆

• S₂F₁₂

Multiple Choice

[3.c]

To find how many S atoms are in 3.0 moles of B₂(SO₄)₃, we would use which setup? Use the mole map for help! (Remember, there are 602 sextillion particles in one mole.)

• $$3.0\ mol\ B_2\left(SO_4\right)_3\left(\frac{3\ mol\ S}{1\ mol\ B_2\left(SO_4\right)_3}\right)\left(\frac{6.02\ x\ 10^{23}\ atoms\ S}{1\ mol\ S}\right)$$

• $$3.0\ mol\ B_2\left(SO_4\right)_3\left(\frac{6.02\ x\ 10^{23}\ atoms\ S}{1\ mol\ S}\right)$$

Multiple Choice

[3.d]

How many moles of oxygen, O₂, will combine with 3.0 moles of copper, Cu_, to form copper(II) oxide, CuO? Show your work and use the mole map!

2 Cu (s) + O₂ (g) --> 2 CuO (s)

• 1.5 moles of O₂

• 3.0 moles of O₂

• 6.0 moles of O₂

Multiple Choice

[3.d]

To find the number of moles of CaBr₂ produced when 160 g of Br₂ (Molar mass = 80 ^g/_mol) react with excess CaI according to the reaction

2 CaI + 2 Br₂ --> 2 CaBr₂ + I₂

You would use which setup? Use your mole map for help!

Multiple Choice

[3.d]

What mass of KClO₃ (Molar mass = 122.5 ^g/_mol) will theoretically produce 48.0 g of oxygen gas (O₂, Molar mass = 32 ^g/_mol)? Show your work and use the mole map!

2 KClO₃ (s) --> 2 KCl (s) + 3 O₂ (g)

• 61.3 g KClO₃

• 74.5 g KClO₃

• 122.5 g KClO₃

Multiple Choice

[3.d]

You react 4.5 g of Fe₂O₃ with excess H₂ and expect to get 3.2 g of Fe according to the equation:

Fe₂O₃ + 3 H₂ --> 2 Fe + 3 H₂O

However, you only get 2.6 g of Fe. What is the percent yield? Show your work!

• 32%

• 58%

• 81%

Multiple Choice

[SC3.e]

"Frosty the snowman...had a corncob pipe and a button nose, and two eyes made out of coal."

If a pre-school teacher in Chicago has 9 buttons and 15 pieces of coal, WHICH WOULD RUN OUT FIRST (buttons or coal) if she sent the kids out to make snowmen after the first snow storm of the year?

• buttons

• coal