By definition, and Arrhenius acid will dissociate in water to release. The increased concentration of causes a drop in pH of the solution. In general, if a hydrogen atom is bound to a very electronegative atom, like in the case of , fluorine tends to take the electron away from hydrogen, resulting in ions. It's a kind of molecule that we call amphoteric, meaning that it can be an acid or a base.
However, because ammonia plays the role of a very weak base, it's mostly thought of as having basic qualities. It has the ability to bind with acids to create an ammonium salt or act as a proton acceptor and become ammonium acid. Also, commonly, acids have the format, where represents a halogen. In another construct, acids ideally have protons that they can donate - this can be observed in and. Commonly, bases have the format, where is any metallic element from the first two columns of the periodic table.
This is seen with , , and. The remaining two options are essentially different "versions" of the same molecule - one just happens to be the protonated form. While is technically amphoteric, it's more so thought of in terms of its basic qualities. When it does act as an acid, it's a very weak acid. Ammonia can easily become ammonium, a proton donator, due to the lone pair of electrons that continue to orbit around the nitrogen center.
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Email address: Your name:. Moving on from water, can we predict whether a compound will be an acid, a base, or neither? We have learned that we can predict many properties of materials by considering their molecular structure. When acids are written in their simplified form for example HNO 3 or H 2 SO 4 it can be very difficult to see any similarities, but if we draw out the Lewis structures some commonalities emerge.
Well, from their formulae it is clear that they all contain hydrogen, but there are many compounds that contain hydrogen that are not acidic. For example, methane CH4 and other hydrocarbons are not acidic; they do not donate protons to other molecules. One common feature of acids is that the proton that gets donated or picked off is bonded to a highly electronegative atom. This atom is often either an oxygen or a halogen such as chlorine Cl , bromine Br , or iodine I. Once you know what to look for, it is quite easy to spot the potentially acidic sites in a molecule.
This way, Chemists can explain chemical reactivity and structure-function relationships of substances. Very early classification systems depended on our senses acids are sour, bases are slippery to the touch and more recent classification systems utilize structural characterization tools such as NMR or crystallography.
Many classification systems have been proposed over the years, and only a few of them have found sufficiently widespread use to end up in textbooks used in the standard Chemistry curriculum. The 2nd through 4th entries are those in common use today.
One then may ask, what's up with the Lux-Flood definition then? This definition is counter to the trend of broadening the classification system, and yet it is useful in describing anhydrous solid-state chemistry and is used to describe geochemical reactions as well as the chemistry of high-temperature melts.
My point being: classification of substances into acids and bases is only meaningful if it helps explain chemical phenomena. Which brings us to the Usanovich definition, which essentially states that every reaction is an acid-base reaction.
Such a broad definition is not overly helpful, and to those of us with an affinity towards electrochemistry ahem , is somewhat arrogant I do believe that determining if a substance will behave as an acid or a base requires a bit of chemical intuition or a Socratic method.
So how do I suggest one use this information to predict whether a substance will behave as an acid or a base using its structure alone? Personally, I find the Lewis theory as the most useful classification system in answering this type of question. If the answer to question 1 is yes, then the molecule can behave as a base.
If the answer to question 2 is yes, then the molecule is an acid. If both are true, then I have an amphoteric substance. In this case, the questions become:. In chemistry, a base is a substance that, in aqueous solution, is slippery to the touch, tastes bitter, changes the colour of indicators e. We would be in trouble, in some cases, where one definition accepts a molecule as acid or base and other not. So, we do have a common definition for acids and bases as mentioned above.
In organic chemistry, whether a compound is acidic or basic can be predicted by looking at the molecular structure and can quite easily be explained by applying the resonance theory. In essence, if the compound can ionize to form a proton and the resulting anion is stable, then the ionization equilibria will be shifted to the right and the compound is acidic.
The more stable the anion, the more acidic the compound is. Consider the following examples:. Introduction and Definitions:. Acids and bases are encountered frequently both in chemistry and in everyday living. They have opposite properties and have the ability to cancel or neutralize each other. Acids and bases are carefully regulated in the body by the lungs, blood, and kidneys through equilibrium processes. Observational definitions: Acids: Bases: Taste sour.
Taste bitter. Give sharp stinging pain in a cut or wound. Feels slippery Turn blue litmus paper red. Turn red litmus paper blue.
Turn phenolphthalein colorless.
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