Corporate Website: http://home.ica.net/~mali/hedd

Email Address: hedd@apexmail.com

Magnesium and Hydrochloric Acid 3

Vinegar and Baking Soda 7

Nitrogen Triiodide 15

Journal Entries (sub-section) 17

Rough Work/Calibration Data (sub-section) 18

Advantages of Device 19

Linear-Representation Diagram 20

Linear-Representation Diagram Guide Sheet 21

Godzilla vs. Hedd Industries Device 22

Works Consulted 23

Mg_(s) + HCl_(aq) Þ MgCl + H_2(g)

For our first reaction we decided to use hydrochloric acid (HCl_(aq)) and magnesium (Mg). We chose this particular reaction due to the fact that we could control the rate of reaction. We had many options in deciding how to do this. The concentration of reactants, temperature, and the addition of a catalyst affect rate of reaction. Temperature is not easy to control with what was available to us and was ruled out. We merely hoped that temperatures in the lab were somewhat constant so as not to affect rates of reaction. We adjusted the concentration of HCl_(aq) to change the rate of reaction. We did not add any catalyst for we felt that the changing of the concentration was sufficient. A representation of the hydrogen chloride molecule is shown in figure 1 using the valence bond theory. It is this molecule that is ionized in hydrochloric acid.

In our device the hydrochloric acid is placed into a burette and set to 0.00 mL. A magnesium strip is placed underneath it. A screw holds down one end of the strip (both ends are looped), while the other end is attached to a weight that sets off the other subsequent reactions when it falls.

Hydrochloric acid is composed of hydrogen and chlorine. Hydrogen chloride (HCI) is a slightly yellow gas that has a pungent, irritating odour. Hydrogen chloride gas readily dissolves in water. The resulting solution is hydrochloric acid. Hydrogen has a 1s orbital while chlorine has an electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁵. Hydrogen and chlorine bond through a covalent bond involving the hydrogen’s lone electron and an electron from chlorine’s 3p orbital. This can be illustrated with an orbital representation diagram.

Hydrochloric acid, it is used to fabricate iron and steel, clean and electroplate metals, etch circuit boards and make solvents, bleaches, chloride salts, fertilizers, dyes, textiles, and rubber. It is also used in analytical chemistry. We could not survive without the compound for our stomachs produce hydrochloric acid to digest food. If this reaction is carried out in a closed system the hydrogen could be collected. If a flame is brought to a small container containing hydrogen there will be a telltale "pop". The hydrogen burns in the presence of oxygen to produce H₂O—a compound essential to all life as we know it.

The molecule is covalently bonded together. Since the electronegativity of hydrogen is slightly lower than the electronegativity of oxygen, they are polar covalently bonded together in H₂O. Since the hydrochloric acid molecule is polar covalently bonded, its opposite ends of the bond carries partial charges of opposite sign, which are attracted to each other with dipole-dipole interaction. Molecules of HCl hold on to each other by weak London forces. In a molecule of water, two hydrogen atoms are polar covalently bonded with an oxygen atom, with hybridized orbital of sp³. A bent non-symmetrical shape is formed with angle of around 104.5 degrees, which leads to a polar covalent molecule. Water molecules are attracted to each other through London forces, dipole-dipole interaction and strong hydrogen bonds. When hydrochloric acid, a polar covalent solute is added to water, a polar covalent solvent, it ionizes 100% in water:

HCl (aq) + H₂O ^{100% ionization} H₃O⁺ + Cl^-

HCl is a strong acid in water because it readily transfers a proton to water to form a hydronium ion:

The equilibrium lies mostly to the right because the conjugate base of HCl, Cl-, is a weak base, and H3O+, the conjugate acid of H2O, is a weak acid.

Magnesium is a silver metal that oxidizes to become a dull silver colour in air. The coating of tarnish on magnesium of MgO acts as a protection that reduces further tarnishing. Mg was isolated for the first time in 1808 by Sir Humphrey Davy (1778-1829), and makes up about 1.93% of the earth’s crust and atmosphere. Magnesium has an electron configuration of 1s²2s²2p⁶3s². Magnesium is a metal and is therefore held together by metallic bonds ("sea of electrons"). This kind of bond makes magnesium somewhat ductile and malleable. Magnesium tends to lose two electrons from the 3s orbital (its outer shell) to achieve stability.

Since the reaction: Mg_(s) + 2H⁺_{(aq) à} Mg²⁺_(aq) + H_2(g) was not in a closed system, an equilibrium is not reached.

In this very reaction, we can see bubbles forming and floating to the surface. These bubbles are actually hydrogen gas that is being formed. The hydrochloric acid is actually dissolving the magnesium away releasing hydrogen gas. In this reaction magnesium is oxidized and hydrochloric acid is reduced (magnesium loses electrons while the hydrochloric acid gains electrons).

As we have seen in our reaction, the magnesium dissolves completely. This means that the magnesium is obviously the limiting reactant in this reaction.

This chemical reaction that occurs between the magnesium and hydrochloric acid was observed to release heat. Systems that release energy to the surrounding are described as exothermic. The energy that is absorbed by the breaking of H₃O⁺ ion into H⁺ and water, is less than the energy released by the formation of hydrogen gas.

The equation involving the heat term can be written as:

Mg_(s) + 2HCl_(aq) à MgCl_(aq) + H_2(g) + nrg

Magnesium loses its electron pair, each H⁺ receives one of the electrons. Two hydrogen atoms them bind together to form hydrogen gas. In our first reaction, only small amount of magnesium were used, and large amount of HCl_(aq) is available. Therefore, there are more H₃O⁺ ions than needed. All the magnesium dissolves into the solution, magnesium is the limiting reactant, therefore a limited amount of H⁺ gas is produced.

In observation of this chemical reaction, heat is being released during the reaction. A system that releases energy is described as exothermic. Since the reaction is exothermic, the energy that is absorbed by the breaking of the hydronium ion into H⁺ and water is slightly less than the energy released when the hydrogen atoms bind together to form hydrogen gas. With other factor such as gas forming, energy is released in the form of heat. The equation will be written as:

Mg_(s) + HCl_(aq) à MgCl + H_2(g) + nrg

This concludes our look at our first reaction of magnesium and hydrochloric acid.

To begin our overview of this reaction a quick history of this reaction’s reactants may prove both interesting and helpful towards understanding it and its applications to our course.

To begin with we have vinegar. Vinegar is a naturally occurring germ killer and was one of the very first medicines known to man. Vinegar and its constituent acid, acetic acid, were most likely first discovered from the fermentation of grapes as the word vinegar comes from a French word meaning sour wine.

Our second reactant, baking soda, or sodium bicarbonate, is a common household chemical. One example of baking soda’s usefulness is its use in baking powder, a mixture containing baking soda, starch, and an acid-forming ingredient which combine to form CO₂ bubbles and make the mixture rise, thus forming a cake. Baking soda is also used in many other types of baked goods.

Now it is necessary, as you have at least a small understanding of the significance of these chemicals in our society, to begin discussing their relevance to our in-class course studies.

Acetic acid is composed of carbon, hydrogen and oxygen. Carbon has the configuration of 1s² 2s² 2p², hydrogen has one electron in its 1s orbital, and oxygen has an electron configuration of 1s² 2s² 2p⁴. Acetic acid has the molecular formula of CH₃COOH and forms the ion CH₃COO ^-.

Acetic acid is a covalently bonded molecule and therefore there shall most likely be only overlapping of s and p orbitals in this molecule. The overlapping of s and p orbitals should be obvious as the electron configurations above demonstrate that these are the only orbitals capable of bonding. The extreme polarity of the ion, formed when CH₃COOH is mixed with water, leads to the polarity of this molecule.

To begin discussion of the bonding arrangement of the acetic acid molecule, an illustration of its structure will be helpful in clarifying any misinterpretations of the following information. The acetic acid molecule is arranged as follows:

The acetic acid molecule is composed of two carbon atoms, one of which has three hydrogen atoms bonded to itself, and the other of which itself forms a carboxyl group. The molecule, being only slightly polar when mixed with water, is not always going to lose the hydrogen atom in its carboxyl group to water even though it consists of two hydrogen atoms that are polar covalently bonded to an oxygen atom, with a hybridized sp³ orbital. The result of CH₃COOH losing an H⁺ ion is the creation of a CH₃COO^-, acetate ion.

The bonds within the acetic acid molecule are not just influenced by intermolecular forces but also intramolecular forces such as London forces, dipole-dipole interaction and strong hydrogen bonds. This strong intramolecular attraction helps to maintain acetic acid as a weak acid as it can hold on to its hydrogen atoms fairly strongly.

One interesting fact about acetic acid is that it also has a second form called the acetic acid dimer. This second form of acetic acid has a molecular formula of C₄H₈O₄ and is created when two standard acetic acid molecules form hydrogen bonds between each other at their carboxylic groups (see figure 2.3).

Since Acetic acid does not conduct electricity well, it is a weak electrolyte. In aqueous acetic acid, only a small fraction (about 0.5%) of the acetic acid molecules have reacted with water to form ions. The remaining 99.5% of the acetic acid molecules exist in the solution almost entirely unionized. Because of its low percentage ionization, acetic acid is classified as a weak electrolyte and a weak acid.

Sodium Bicarbonate is composed of sodium, oxygen, hydrogen and carbon. Sodium has a configuration of 1s² 2s² 2p⁶ 3s¹, oxygen has an electron configuration of 1s² 2s² 2p⁴, hydrogen has one electron in its 1s orbital, while carbon has the configuration of 1s² 2s² 2p².

Sodium bicarbonate is a solid bonded ionically. When this substance is placed in acetic acid bubbles of CO₂ are formed as sodium bicarbonate dissolves. The chemical equations are:

NaHCO₃ (S)+ HC₂H₃O₂ (l) à NaC₂H₃O₂ (aq) + H₂CO_{3 (aq)}

H₂CO_{3 (aq)} à H₂O _(l) + CO_{2 (g)}

When sodium bicarbonate and acetic acid react sodium acetate, water and carbon dioxide are the final products. Carbonic acid is produced in the reaction but due to its instability it decomposes to H₂O and CO₂.

Upon observing this reaction it was agreed upon that heat was being released. A reaction that releases energy is to be described as an exothermic reaction. Since the reaction is exothermic, the energy absorbed by the breaking of the acetic acid and sodium bicarbonate into H⁺ and CH₃COO^-, and Na⁺ and HCO₃ is slightly less than the energy released when the hydrogen and bicarbonate bond and the sodium and acetate bond. The overall thermodynamic equations of this reaction can be written as:

NaHCO_{3 (aq)} + CH₃COOH _{(aq) «} NaCH₃COO^- _(aq) + H₂O _(l) + CO_{2 (g)}+ nrg

The energy of the product is less than that of the reactants so this makes the reaction an exothermic one. Unfortunately we do not know the exact value in kJ/mol of the energy released, but the heats of formation of acetic acid and sodium bicarbonate are

–108.6 kJ/mol and –947.7 kJ/mol respectively.

Two of the most important factors affecting the rate of this reaction are the nature of the reactants and the conditions under which the reactions occurred. There are five factors that affect the rate of reactions and these are:

1. The chemical nature of reactants.
2. The concentration of the reactants.
3. The ease at which the reactants to come into contact with each other.
4. The temperature of the system.
5. The presence of a catalyst.

This reaction was affected by factors # 1, 3, and 4. The temperature of the system would have played a role in the speed the reaction occurred at, as this reaction did occur both fast and slow. The nature of the reactants played a large role as an acid-base reaction occurred, and the ease at which the substances came in to contact with each other allowed either more or less (depending on circumstance) CO₂ to be created.

The last topic related to our in class course work is the relationship of this reaction with acid-base and equilibrium subject matter.

Consider the reaction:

NaHCO_{3 (aq)} + CH₃COOH _{(aq) «} NaCH₃COO^- _(aq) + H₂O _(l) + CO_{2 (g)}

You can see that this reaction can shift either left or right, yielding products or reactants. This is the concept behind chemical equilibria and this reaction certainly follows the guidelines of equilibrium. Equilibrium occurs as a process where the reactants do what they do and react to produce products. As the concentration of products increases, their ions "bump" into one another more frequently. Because of this the reverse reaction (products to reactants) occurs faster and more frequently. At some point the concentration of the products become big enough to make the forward and reverse rates of reaction equal, and equilibrium is achieved. In the case of the acetic acid and baking soda the equilibrium lies somewhere on the right, indicating that few reactants are remaining after the reaction has begun, also, this indicates that the reaction’s equilibrium constant would be fairly large.