Chapter 8: Chemical Equations

I'd like you to read the first two thirds of the chapter.

11th Edition: pages 150-165.
12th Edition: pages 150-164.

The picture shown in the textbook and here is a mixture of aluminum powder and iron (III) oxide powder. Once ignited the aluminum rips the oxygen off of the iron oxide resulting in molten iron, which falls down to the below pot of sand. One time someone used wet sand, which was a mistake because the molten iron turned the water to steam instantly. This sprayed molten iron all over the front two rows of students.

Problem 1 :

11th Edition: Question 11, page 170.
12th Edition: Question 3, page 172.
Balance the following equations: I will give the type of reaction

(a) H₂ + O₂ --> H₂O
Combustion reaction because of oxygen. It also qualifies as a combination or synthesis reaction.
(b) C + Fe₂O₃ --> Fe + CO
This is a single replacement (displacement) reaction. The carbon atom(s) replaces the iron. This is reaction shows how to turn iron ore into metallic iron.
(c) H₂SO₄ + NaOH --> H₂O + Na₂SO₄
                                --> HOH + Na₂SO₄
This is a double replacement reaction and also called a neutralization reaction. It's a bit hard to see the double-replacement. If water is written as HOH, you can tell that the first H is the one that came from sulfuric acid and replaced the sodium (Na).
(d) Al₂(CO₃)₃ --> Al₂O₃ + CO₂
This is a decomposition reaction. Most carbonates (CO₃) will decompose to CO₂.
(e) NH₄I + Cl₂ --> NH₄Cl + I₂
This is a single replacement reaction. The more reactive chlorine takes iodine's place.

Problem 2 :

11th Edition: Question 17, page 171.
12th Edition: Question 7, page 172.
Balance the following equations: (I will comment on the reaction)
(a) MnO₂ + CO --> Mn₂O₃ + CO₂
Carbon monoxide is commonly used to strip off oxygen atoms from metals. This reaction shows the first step. If more CO is present, eventually all oxygen atoms will be grabbed by CO and manganese (Mn) metal will be left. This is how metal ores get converted to metals.

(b) Mg₃N₂ + H₂O --> Mg(OH)₂ + NH₃
The burning of magnesium metal ribbons in chemistry labs is a common demonstration (2Mg + O₂ --> MgO). After burning, they point out the white powder residue, and say that is magnesium oxide (MgO). Because air is mostly nitrogen, there's also some magnesium nitride produced (Mg₃N₂). If some water is added to the white powder, you will smell ammonia. That can't happen if the powder is only magnesium oxide (MgO). You might stump your lab instructor with that observation.

(c) C₃H₅(NO₃)₃ --> CO₂+H₂O+N₂+O₂

Whenever you see NO₃ in a formula, watch out. It's often explosive or at least creates oxygen to make something explosive. Also, whenever a reaction produces a lot of gases like here, then it's usually an explosive. Explosive power comes from a lot of gases being produced in a closed area at a fast rate. The starting material here is nitroglycerin. Interestly, nitroglycerin (diluted) is also used for medical purposes.
Extra Question: Go to this link and report on the medical use of nitroglycerin.
http://en.wikipedia.org/wiki/Nitroglycerin

(d) FeS + O₂ --> Fe₂O₃ + SO₂
Hint: When balancing this equation, balance the irons first, then the sulfur. In equations with O₂, alway save the O₂ for last.

(e) Cu(NO₃)₂ --> CuO + NO₂ + O₂

Like mentioned on (c), nitrates are often a source of oxygen and belong to a class of compounds called oxidizers. They are often used in fireworks. Copper compounds are often blue and flames in contact with copper are also blue.

(f) NO₂ + H₂O --> HNO₃ + NO
Your automobile produces nitrogen dioxide because combustion in the cylinders convert some nitrogen in the air to various nitrogen oxides. In contact with water, nitrogen dioxide turns into nitric acid and nitrogen monoxide. Both are unhealthy.

(g) Al + H₂SO₄ --> Al₂(SO₄)₃ + H₂
Many metals are dissolved by sulfuric acid. Acids have an "H+" ion, which is short one electron. Many metals have their outer electrons pulled off by the "H+" ion. When that happens, the metal dissolves. This equation is somewhat simplified because it doesn't show these as ions dissolved in water. Here is the full balanced equation with the ions. You might use it to solve for the above equation:
2Al_(s) + 6H⁺_(aq) + 3SO₄^2-_(aq) --> 2Al³⁺_(aq) + 3SO₄^2-_(aq) + 3H_2(g)

(h) HCN + O₂ --> N₂ + CO₂ + H₂O
This equation is ironic. HCN is hydrogen cyanide, the poison used in the gas chambers in World War II. If burned, the hydrogen cyanide is made completely harmless.


(i) B₅H₉ + O₂ --> B₂O₃ + H₂O
This is where symbolic equations are very misleading. B₅H₉ is called pentaborane and is one of the most dangerous compounds around. It's a powerful rocket fuel that the military nicknamed the Green Dragon because of the green flame. Low doses can cause kidney failure and nervous system damage. Exposure to the air can make it explode as well as any hard bumps. Therefore, when balancing this equation, be extra careful not to shake the table.

For students in my class, send your answers to chm130@chemistryland.com. Use a subject line of Chapter 8.