• Consider the reaction:

Fe3O4 + 4 C 3 Fe + 4 CO

What is the maximum mass of Fe which could be made from 115.0 g Fe3O4 of and 24.00 g C?

The trick here is to find the maximum amount of iron which could be made from each reactant. The lesser amount will then be the max possible:

C: (3 mol Fe/ 4 mol C)(24.00 g C/ 12.01 g C/mol C) = 1.499 mole

Fe3O4: (3 mol Fe/ mol Fe3O4)(115.0 gFe3O4/231.6 g Fe3O4/mol Fe3O4) = 1.490 mole

C: (3 mol Fe/ 4 mol C)(24.00 g C/ 12.01 g C/mol C) = 1.499 mole

Fe3O4: (3 mol Fe/ mol Fe3O4)(115.0 gFe3O4/231.6 g Fe3O4/mol Fe3O4) = 1.490 mole

\ Fe3O4 limits, can only make 1.490- moles.

So mass is then= (1.490 moles) (55.85 g/mole) = 83.22 g Fe

### Solubility Rules

It is useful to remember some simple "rules" (really more like guidelines) to help in predicting reactions. For common compounds such as we see in general chemistry we can use the following rules:

1. Nitrates (NO3-) are all soluble.
2. Alkali metal (Li+, Na+, K+, Cs+, and Rb+) and ammonium (NH4+) salts are all soluble, with the exception of a few Lithium salts.
3. Chloride, bromide, and iodide (Cl-, Br-, and I-) salts are generally soluble, except for the salts of silver, lead(II) and mercury(I) (Ag+, Pb2+ and Hg22+).
4. Sulfates are soluble, except for the salts of barium {BaSO4}, lead(II) {PbSO4}, mercury(II) {HgSO4}, and calcium {CaSO4}.
5. Most hydroxides are only slightly soluble (but see rule 2).
6. Sulfides (S2-), carbonates (CO32-), phosphates (PO43-), and chromates (CrO42-) are only slightly soluble (but see rule 2).

Examples using these rules may be found in the Module

### Most Reactive

H2 released in cold water

K

Ba

Sr

Ca

Na

H2 released in steam

Mg

Al

Mn

Zn

Cr

Fe

Cd

H2 released in acids

Co

Ni

Sn

Pb

H2

H2 not released

Sb

Bi

Cu

Ag

Hg

Pd

Pt

Au