GENERAL CHEMISTRY I
CHEM 1311.001
EXAM 2
Friday October 17, 1997

Name___________________________________

SSN____________________________________

IONIC COMPOUNDS CONTAINING ONLY MONATOMIC IONS

1. What is the formula of potassium nitride?
a) KNb) K2Nc) KN2 d) K3Ne) KN3
f) K2N3g) K3N2 h) K4N3i) K3N4
2. What is the formula of sodium oxide?
a) NaOb) Na2Oc) NaO2 d) Na3Oe) NaO3
f) Na2O3g) Na3O2 h) Na4O3i) Na3O4
3. What is the formula of aluminum fluoride?
a) AlFb) Al2Fc) AlF2 d) Al3Fe) AlF3
f) Al2F3g) Al3F2 h) Al4F3i) Al3F4
4. What is the formula of potassium chloride?
a) KClb) K2Clc) KCl2 d) K3Cle) KCl3
f) K2Cl3g) K3Cl2 h) K4Cl3i) K3Cl4
5. What is the formula of barium nitride?
a) BaNb) Ba2N c) BaN2d) Ba3N e) BaN3
f) Ba2N3 g) Ba3N2 h) Ba4N3 i) Ba3N4
IONIC COMPOUNDS CONTAINING AT LEAST ONE POLYATOMIC ION


6. What is the formula of sodium carbonate?
a) NaCO3 b) Na2CO3 c) Na(CO3)2 d) Na3CO3
e) Na(CO3)3 f) Na2(CO3)3 g) Na3(CO3)2 h) Na4(CO3)3
i) Na3(CO3)4
7. What is the formula of ammonium phosphate?
a) NH4PO4 b) (NH4)2PO4 c) NH4(PO4)2 d) (NH4)3PO4
e) NH4(PO4)3 f) (NH4)2(PO4)3 g) (NH4)3(PO4)2 h) (NH4)4(PO4)3
i) (NH4)3(PO4)4
8. What is the formula of iron(II) sulfate? (Hint: Note that this is a Stock name. Try to remember the meaning of the Roman number that appears in Stock names, so you'll know how to write the formula.)
a) FeSO4 b) Fe2SO4 c) Fe(SO4)2 d) Fe3SO4 e) Fe(SO4)3
f) Fe2(SO4)3 g) Fe3(SO4)2 h) Fe4(SO4)3 i) Fe3(SO4)4
MASS PERCENTAGES AND EMPIRICAL FORMULAS


9. Calculate the percent by mass of hydrogen in ammonia, NH3. Fully show your work. Be as neat and organized as possible. Clearly label your final answer. If you are unable to obtain the correct answer, you may receive partial credit based on the quality of your work and your apparent understanding of the problem.

10. A compound containing only the elements nitrogen and oxygen was found to be 30.45% nitrogen by mass. Determine the empirical formula of this compound. Fully show your work. Be as neat and organized as possible. Clearly label your final answer. If you are unable to obtain the correct answer, you may receive partial credit based on the quality of your work and your apparent understanding of the problem.

ANSWERS:

1)  d       2)  b       3)  e       4)  a       5)  g      

6)  b       7)  d       8)  a       9)  17.76% H       10)  NO2

Work for # 9:

for NH3   MWT = 14.00674 + 3 (1.00794) = 17.03056

Mass contribution from H = 3 (1.00794) = 3.02382

%H = 100% (contribution from H / MWT)

%H = 100% ( 3.02382 / 17.03056 ) = 17.76%

Work for # 10:

Assume you have 100.00 g of the compound. In that case, the percentages become the masses. Therefore, you have 30.45 g of nitrogen. The remaining mass, 69.55 g, must be oxygen. Convert these masses to moles:

30.45 g N ( 1 mol N / 14.00674 g N ) = 2.174 mol N

69.55 g O ( 1 mol O / 15.9994 g O ) = 4.347 mol O

Ratio is 2.174 : 4.347    ( N : O )

We need to find the equivalent integer ratio. Try dividing both numbers in ratio by the smaller of the two numbers.

2.174 / 2.174 = 1

4.347 / 2.174 = 1.999540018

Within roundoff error, the number 1.999540018 is acceptably close to the integer 2.

Threfore, the ratio is 1 : 2   ( N : O ) making the formula NO2

This page was last modified Tuesday March 23, 1999