Introduction
This series of posts seeks to present the material covered in the first semester of a college level general chemistry course, in an easily digestible steemit blog post format. The series is intended to be read, and experienced in sequential order starting with Post 1. The material will build upon itself, and potential exercises included (problem sets), will pertain to the post they are contained in, or any previous post. Each post will pick up immediately where the previous in the series left off. Please check out the #chemistry-lesson tag for all posts in this series. I hope you find this series to be informative and beneficial toward your understanding of chemistry and science in general.
Immediate Preceding Post
Part 5: Chemical Reactions…Continued
Legend for This Section
As subscripts do not currently work on steemit, to symbolize when a number should be sub-scripted I will be writing it in the text as follows: /x/.
What Does Aqueous Mean?
Most chemical reactions occur by mixing components together into some sort of solution. A solution is just defined as the mixture of two or more substances. The most common type of solution in which chemistry occurs in is an aqueous solution. To understand this “aqueous” term let us first define two other terms: solute and solvent. Were we to mix together two components into a solution our solute would be the substance there was less of and our solvent would be the substance there was more of. Solutions can take many forms, they can be composed entirely of gasses, a mixtures of liquids or even a mixture of solids. An aqueous solution is one where the solute is a pure liquid or solid dissolved in a liquid, and the solvent is water. Aqueous reactions are those which occur in water. Whenever we indicate that a component of a reaction is an aqueous solution we give it the phase term (aq).
Solutes Dissolving In Water
When a solute dissolves into water, the aqueous solution that is formed is either an electrolytic solution (one which contains an electrolyte) or a non-electrolytic solution (does not contain an electrolyte). When you buy your favorite sports drink from the store it will likely boldly state that it is fortified with electrolytes! What this means is that dissolved in the water (solvent) is a solute which forms an electrolytic solution. An electrolyte is a solute that allows for electricity to be conducted once it’s dissolved in water. A non-electrolyte, well it just won’t conduct electricity when it’s dissolved in water. Some common examples of electrolytes (like the ones found in your sports drink) are table salt (NaCl) and Potassium Chloride (KCl). And an example of a non-electrolyte would be table sugar or sucrose (C/6/H/22/O/11/).
Source 2
Let’s look at the reaction of KCl dissolving in water and becoming an electrolyte:
Here what happens, is the Solid KCl salt, an ionic compound (Covered in Part 3) is placed into water. When this happens the salt breaks apart into its respective ions. This happens though a process called hydration. Where each ion gets surrounded by water molecules (as water molecules are polar a topic which will be covered very soon!) pulling them into solution.
Solids are not the only phase of a molecule that can be hydrated and ionized in its aqueous form! Both gasses and some fully hydrated aqueous molecules can be split into their ions when in aqueous solutions! Now that we know about aqueous solutions lets discuss the types of reactions that can occur in them!
Acid – Base Reactions
The first type of reaction we will discuss is one of the most common chemical reactions, the reaction of an Acid with a Base. An acid is any molecule which ionizes in water and forms H+ ions. While a base is any molecule which ionizes in water and forms OH- ions. This definition of an acid/base is known as the Arrhenius Acid/Base. This definition of an acid/base only applies to aqueous solutions, and so some other scientists (Johannes Bronsted and Martin Lowry) came up with a better, more encompassing definition. In their definition an acid is anything that donates a proton (H+ will interchangeably be referred to as a proton), and a base is anything that accepts a proton. All Arrhenius acids and bases are also Bronsted/Lowry acids and bases, but not vice-versa. The Arrhenius definition fits because in that theory the acid donates an H+ to H/2/O and forms H/3/O+ and a Base accepts a proton from water leaving behind an OH-. The acid is still a proton donor, and the base still a proton acceptor. Let’s look at some examples of acids and bases!
Here in our first example (Ex. 1) we are looking at a monoprotic acid (monoprotic meaning it releases one proton), this is the acid ionization of hydrochloric acid. In our second example (Ex. 2) we are looking at a diprotic acid (diprotic meaning it releases two protons), the first reaction is the release of the first proton from sulfuric acid, when that happens it leaves behind the HSO/4/- ion, which can also release a proton of its own, that is shown in the second reaction where hydrogen sulfate dissociates into a proton and a sulfate ion (SO/4/2-). Example three (Ex. 3) is that of a Bronsted-Lowry acid/base, here the proton (H+) is acid (it donates itself) and water is a base (it accepts the proton), you will note that water is described not as aqueous but rather with an (l) which indicates that it is a pure liquid. After accepting the proton it forms H/3/O+ which is called the hydronium ion.
Our fourth example (Ex. 4) is the reaction for the solubilization of the base Sodium Hydroxide, here the solid sodium hydroxide is split up into its ionic components a positively charged sodium ion and the negatively charged Hydroxide polyatomic ion. Example 5 (Ex. 5) is a similar reaction however this compound Calcium Hydroxide splits into one Positive Calcium ion (Ca+2) and two negative hydroxide ions (this is because the solid salt must have a neutral charge). In both Ex 4 and Ex 5, the basic component is the same the Hydroxide ion. This is illustrated in Ex 6. Here we see that OH- is a Bronsted-Lowry base as it is able to accept a proton and form water.
Reacting an Acid with a Base
We are all familiar with what happens when we mix an acid, vinnegar (acetic acid: CH/3/COOH), with a base, baking soda (sodium bicarbonate: NaHCO/3/):
We get a lot of bubbling going on! This happens because of the reaction between the acid and the base! It happens with the following reaction:
Here the acetic acid CH/3/COOH is the proton donor, and the sodium bicarbonate is the proton acceptor, except when it accepts a proton it degrades into carbon dioxide and water! This is why you get the bubbles, it’s the generation of CO/2/. This reaction is a unique case, in general acids and bases do not break down. So let is look at a two aqueous acid-base reaction examples:
Here in Example 7 (Ex. 7) We are looking at the reaction between Hydrochloric Acid and Sodium Hydroxide, both compounds are indicated as aqueous and so we already know that these split up into their respective ions (I will get into more details about why at a later date), so we split them up into those ions. We see that we have H+ and OH- which react to form water. At the end of the reaction we are left with water and the aqueous sodium ion and aqueous chloride ion.
In example 8 (Ex. 8) we are looking at the reaction between Perchloric acid and Barrium hydroxide, as with the previous example we split these two aqueous compounds up into their ions, react any available protons with any available hydroxides (we have two of each) and form water. This leaves us with 2 waters, one barium ion (Ba2+ and 2 perchlorate ions (ClO/4/-).
End of Aqueous Chemical Reactions 1 Problem Set
We’ve reached the end of this section, and as with the end for previous sections, I will provide you with a problem set so you could test yourself to see if you are fully understanding the material.
Problem Set 5
Problem Set 5 Answer Key
Future Posts
Subsequent posts will cover: Acids Bases and other Aqueous Reactions, Electronic Configuration of Atoms, Chemical Bonding, and Molecular Geometry, and more.
Reference Figure: Periodic Table
Other References
Constants and Conversions List
Source for Additional Constants
Some Common Ions
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