Chemistry 1210 – F20 NAME ___________________________ Dr. Joe Casalnuovo Midterm #1

***CLOSED BOOK EXAM - No books or notes allowed. ***Please put your name on all of the test pages. ***Be sure your exam has 9 questions on 4 pages!!! ***A periodic table is attached to the back.

Potentially useful information: Avogadro's number = 6.022 x 1023 ________________________________________________________________

1. (36 pts) For parts i - ix, circle the correct answer. Only one answer per problem (4 pts each).

No partial credit. (i) When the calculation below is carried out, what is the number of significant figures in

the answer? (Assume that both numbers are measured—not exact—values.)

72.1123 - 71.3 =

(a) 1 (b) 2 (c) 3 (d) 4 (e) 5 (ii) During the historical development of chemistry, the following ideas were proposed by

various scientists. Which one is considered incorrect according to modern chemistry?

(a) All atoms of a given element are identical. (b) In any chemical reaction, mass is neither created nor destroyed. (c) A chemical reaction merely consists of a rearranging of atoms from one set of

combinations to another. (d) The periodic table should be arranged so that elements with similar properties and

reactivity fall in the same column. (e) In any sample of a pure chemical substance, you will always find the same

elements in the same definite proportions by mass.

(iii) Naturally occurring lithium is composed of only two isotopes, 6Li (mass = 6.0169 amu) and 7Li (mass = 7.0183 amu). Which statement about the two isotopes is true?

(a) The natural abundance of 6Li must be greater than the natural abundance of 7Li. (b) The natural abundance of 6Li must be equal to the natural abundance of 7Li. (c) The natural abundance of 6Li must be less than the natural abundance of 7Li. (d) The two isotopes contain the same number of neutrons. (e) The two isotopes contain different numbers of protons.

Name: _________________________ (iv) Give the answer that shows all of the compounds in the following list that are

expected to exist entirely as molecules: C3H8, MgCl2, Zn(NO3)2, OCl2. (a) C3H8 (d) MgCl2, Zn(NO3)2 (b) C3H8, Zn(NO3)2, OCl2 (e) C3H8, MgCl2, Zn(NO3)2, OCl2 (c) C3H8, OCl2 (v) Which series of elements shown below contains only elements that form cations of only one

oxidation state? (a) K, Al, Ca, Cl (d) F, Cl, O, S (b) Cs, Ba, Cr, Mg (e) Li, Al, K, Sr (c) H, Au, Na, Sn (vi) What is the mass percentage of nitrogen in Cu(NO3)2? (a) 7.469 (b) 11.16 (c) 8.072 (d) 14.94 (e) 16.14 (vii) The empirical formula of a certain compound is CHCl. The molar mass of this compound

is 290.8 g/mol. How many atoms of carbon does a molecule of this compound contain? (a) 1 (b) 6.022 x 1023 (c) 3.613 x 1024 (d) 6 (e) 8

(viii) Consider the balanced reaction below:

2 Li + F2 ¾® 2 LiF

If 1 mol of Li is combined in a vessel with 1 mol of F2, what will be present in the beaker after the reaction is complete?

(a) 0.5 mol F2 and 1 mol of LiF (d) 0.5 mol Li and 1 mol of LiF (b) 1 mol of LiF (e) 0.5 mol F2 and 2 mol of LiF (c) 0.5 mol F2 and 0.5 mol of LiF (ix) How many carbon atoms are there in 1.88 g of dibromoethane, C2H4Br2? (a) 1.13 x 1024 (b) 6.09 x 1021 (c) 2 (d) 1.21 x 1022 (e) 2.26 x 1024

Name: _________________________ 10. (8 pts) Complete the following table.

Complete Symbol

Atomic Number

Mass Number

Number of Protons

Number of Neutrons

Number of Electrons

7935 Br-

26 14 10 11. (5 pts) Give the names of the following: (a) TiO2 __________________________________________

(b) HCl ________________________________________________

(c) Cl2O5 ______________________________________________ (d) CoF3 _____________________________________________ (e) BCl3 _____________________________________________ 12. (5 pts) Give the chemical formulas of the following: (a) calcium hydride _______________________________________ (b) iodine heptachloride _______________________________________ (c) sulfur tetrafluoride _________________________________

(d) vanadium(V) sulfide _____________________________________

(e) aluminum oxide _____________________________________ 13. (6 pts) Briefly explain the difference between a scientific law and a theory. How are they

related to each other?

Name: _________________________ 14. (8 pts) Balance the following equations (a and b). No partial credit. (a) ____ C2H6 + ____ O2 ¾® ____ CO2 + ____ H2O (b) ____ Fe + ____ H2O ¾® ____ Fe3O4 + ____ H2 15. (10 pts) An elemental analysis shows that a certain compound contains 63.2 % carbon, 5.26%

hydrogen, and 31.6 % oxygen by mass. What is the empirical formula of the compound? Show all work.

16. (10 pts) For the reaction below, if 0.45 g of Al is produced from 3.00 g of Al2O3, what is the

percent yield? Show all work.

2 Al2O3 ¾® 4 Al + 3 O2

17. (12 pts) If 0.505 g of potassium superoxide, KO2, is reacted with 0.0766 g of water, what is the

maximum mass of oxygen, O2, that could be produced? Show all work.

4 KO2 + 2 H2O ¾® 4 KOH + 3 O2

Name: _________________________