Exam 1 (2)

1. What is the empirical formula of a compound that is 62.0% C, 10.4% H, and 27.5% O by mass?

1. C₅H₁₀O₂
2. C₆HO₃
3. C₃HO
4. C₆H₁₂O₂
5. C₃H₆O

2. What is the stoichiometric coefficient for oxygen when the following equation is balanced using the lowest, whole-number coefficients?
_____ C ₂H ₆O  ( l) + _____ O ₂( g) → _____ CO ₂( g) + _____ H ₂O( l)

1. 3
2. 5
3. 7
4. 9

3.  How many moles of PCl ₃ contain 3.68 × 10 ²⁵ chlorine atoms?

1. 61.1 moles PCl₃
2. 20.4 moles PCl₃
3. 49.1 moles PCl₃
4. 16.4 moles PCl₃
5. 54.5 moles PCl₃

4.  A sample of pure calcium fluoride with a mass of 15.0 g contains 7.70 g of calcium. How much calcium is contained in 40.0 g of calcium fluoride?

1. 20.5 g
2. 15.0 g
3. 2.27 g
4. 7.70 g

5.  Which are isotopes? An atom that has an atomic number of 20 and a mass number of 42 is an isotope of an atom that has

1. 22 neutrons and 20 protons.
2. 22 protons and 20 neutrons.
3. an atomic number of 20 and a mass number of 40.
4. an atomic number of 21 and a mass number of 42

6  Which of the following is a transition element?

1. Sn
2. Pr
3. U
4. K
5. Pd

7.  Calculate the atomic mass of element “X”, if it has 2 naturally occurring isotopes with the following masses and natural abundances:

X-45 44.8776 amu 32.88%
X-47 46.9443 amu 67.12%

1. 46.26 amu
2. 45.91 amu
3. 46.34 amu
4. 46.84 amu
5. 44.99 amu

8.  The Scientific Method

1. is a framework for proving an argument you know to be true.
2. is just a theory.
3. is a strict set of rules and procedures that lead to inarguable fact.
4. is based on continued observation and experiment.
5. isn’t used much in modern chemistry

9.  An alligator is 152.4 cm long. How long is he in feet?

1. 32.2 ft
2. 5.00 feet
3. 12.7 ft
4. 720.0 ft
5. 60.0 ft

10. Which of the following statements is TRUE?

1. An observation explains why nature does something.
2. Once a theory is constructed, it is considered fact.
3. A hypothesis is speculation that is difficult to test.
4. A scientific law is fact.
5. A scientific law summarizes a series of related observations