Item number 5 Formula Mass Computations (in amu) – Table 2

MgO

Mg = 24.305 O = 15.999

Mr = 24.305 + 15.999 = 40.304

K2S

K = 39.098 S = 32.065

Mr = 2(39.098) + 32.065 = 110.26 amu

C3H8O3

C = 12.011 H = 1.008 O = 15.999

Mr = 3(12.011) + 8(1.008) + 3(15.999) = 92.09 amu

Ca (NO3)2

Ca = 40.078 N = 14.007 O = 15.999

Mr = 40.078 + 2[14.007 +3(15.999)] = 164.09 amu

Mg3 (PO4)2

Mg = 24.305 P = 30.964 O = 15.999

Mr = 3(24.305) + 2 [30.964 + 4(15.999)] = 262.84 amu

C6H2CH3 (NO2)3

C = 12.011 H = 1.008 O = 15.999 N = 14.007

Mr = 7(12.011) +5(1.008) + 3[14.007 +2(15.999)] = 227.1 amu

Pt (NH3)2Cl2

Pt = 195.084 N = 14.007 H = 1.008 Cl = 35.453

Mr = 195.084 + 2[14.007+ 3(1.008)] = 300.1 amu

Fe (ClO4)2

Fe = 55.845 Cl = 35.453 O = 15.999

Mr = 55.845 + 2 [35.453 + 4(15.999)] = 254.74 amu

Na2CO3 • 10H2O

Na= 22.99 C = 12.011 O = 15.999 H = 1.008

Mr = 2(22.99) + 12.011 + 3(15.999) + 10[2*1.008 + 15.999] = 286.1 amu

MgSO4 • 7H2O

Mg = 24.305 S = 32.065 O = 15.999 H = 1.008

Mr = 24.305 + 32.065 + 4(15.999) + 7 [2*1.008 + 15.999] = 246.5 amu

Item number 3 Formula Mass Computations (in amu) – Table 1

KCl

K = 39.098 Cl = 35.453

Mr = 39.098 + 35.453 = 74.551 amu

H2O

H = 1.008 O = 15.999

Mr = 2(1.008) + 15.999 = 18.02 amu

CaSO4

Ca = 40.078 S = 32.065 O = 15.999

Mr = 40.078 + 32.065 + 4(15.999) = 136.14 amu

NH3

N = 14.007 H = 1.008

Mr = 14.007 + 3(1.008) = 17.03 amu

Hg (NO3) 2

Hg = 200.59 N = 14.007 O = 15.999

Mr = 200.59 + 2[14.007 + 3(15.999)] = 324.60 amu

Refer to a periodic table, as needed, to answer these questions.

Section 1: In-Class Practice

1. How does the structure of an ionic compound differ from that of a molecular compound?

Ionic compounds are formed by the transfer of electrons while molecular compounds are formed by sharing of electrons. In addition to that, ionic compounds are formed via ionic bond between a metal and non-metal while molecular compounds are formed via covalent bond between two non-metals.

2. Distinguish among the terms molecular mass, formula mass, and molar mass (the mass of a mole).

Molar mass is the mass of one mole of a substance. For example the molar mass of H2O is 18.015 grams.

Formula and molecular mass are measured in terms of AMU (Atomic Mass Unit). Formula mass refers to the mass of an ionic compound. For example we refer to the 58.5 AMU mass of NaCl as its formula mass since NaCl is ionic. On the other hand, molecular mass refers to the 67.82 AMU mass of Boron Triflouride as molecular mass since it is a molecule.

3. Complete Table 1 by

· Indicating whether each compound is ionic or molecular (Column 2)

· Noting whether each compound's basic unit is a formula unit or a molecule (Column 3)

· Using the periodic table and a calculator to calculate the formula masses for each compound (Column 4)—show your work on a separate piece of paper

4. Calculate the formula mass of the hydrate, CuSO4 • 5H2O. Show your work.

Formula Masses (in amu):

Cu = 63.546 S = 32.065 O = 15.999 H = 1.008 O = 15.999

Mr = 63.546 + 32.065 + 4 (15.999) + 5 [2(1.008) + 15.999]

Mr = 249.7 amu

Section 2: Out-of-Class Practice

5. Complete Table 2 by calculating the formula mass of each compound listed. Show your work on a separate sheet of paper.

6. Put a check beside each of the compounds in Table 2 for which you calculated the molecular mass.

7. Oxygen gas is diatomic, meaning that it is made up of two oxygen atoms. What would be the molecular mass of oxygen gas? Would it differ from the atomic mass of oxygen? If so, how?

Diatomic oxygen is O2. Molecular mass of oxygen gas = 2(15.999) = 31.998 amu

Thus, the molecular mass of oxygen gas is 31.998 amu. It differs from the atomic mass of oxygen gas since this value is only 15.999 amu.

8. What is the formula unit of aluminum chloride, Al2Cl6? What about the formula unit for ethane, C2H6? (Hint: Remember the difference between ionic and molecular compounds.)

The formula unit is the lowest ratio of ions represented in a compound. Thus, Al2Cl6 has a formula unit of AlCl3 with ions Al+3 and Cl-1. For C2H6, the lowest ratio is CH3.

Conclusion

Now address the Focus Question: Which has more mass—salt (NaCl) or sugar (C12H22O11)? Show calculations to support your answer.

Sugar (C12H22O11 has more mass than salt (NaCl) .

For NaCl:

Na = 22.99 Cl = 35.453

Mr = 22.99+ 35.453

Mr = 58.443 amu

For C12H22O11:

C = 12.011 H = 1.008 O = 15.999

Mr = 12(12.011) + 22(1.008) +11(15.999)

Mr = 342.3 amu