If we look at the formulas of different acids, we can see that they all contain at least one H hydrogen — for example:. When we put a molecule of acid into water, it breaks apart. The science term for this is that it dissociates. The chemical difference between acids and bases is that acids produce hydrogen ions and bases accept hydrogen ions. A base is a substance that neutralises acids. When bases are added to water, they split to form hydroxide ions, written as OH -.
We call a base that has been added to water an alkaline solution. If we look at some formulas for bases, we can see that they all contain hydroxide OH - ions — for example:. If an acid and a base are added together, they react to form water H 2 O and a salt. An example you might be familiar with is brushing your teeth. The acid created from the bacteria on your teeth reacts with the base in your toothpaste.
This reaction is called neutralisation. A pH meter measures how acidic or basic a solution is. When we test a substance with a pH meter, we get a number from 0— This is a pH scale, and it can be used to compare substances. It is important to know that this scale is logarithmic. The alkaline earth metal hydroxides are less soluble but are still considered to be strong bases. Lewis bases and acids : A list of various Lewis bases right and Lewis acids left.
Part 1 — What the Heck is an Acid or Base? Were you ever super confused in high school or college chemistry? An Arrhenius acid dissociates in water to form hydrogen ions, while an Arrhenius base dissociates in water to form hydroxide ions. An acid-base reaction is a chemical reaction that occurs between an acid and a base. Several concepts exist that provide alternative definitions for the reaction mechanisms involved and their application in solving related problems.
Despite several differences in definitions, their importance as different methods of analysis becomes apparent when they are applied to acid-base reactions for gaseous or liquid species, or when acid or base character may be somewhat less apparent. The Arrhenius definition of acid-base reactions, which was devised by Svante Arrhenius, is a development of the hydrogen theory of acids. This led to Arrhenius receiving the Nobel Prize in Chemistry in The Arrhenius definitions of acidity and alkalinity are restricted to aqueous solutions and refer to the concentration of the solvated ions.
Under this definition, pure H 2 SO 4 or HCl dissolved in toluene are not acidic, despite the fact that both of these acids will donate a proton to toluene. Thus, the Arrhenius definition can only describe acids and bases in an aqueous environment. An Arrhenius acid-base reaction is defined as the reaction of a proton and an hydroxide ion to form water:.
Chemistry Part 1 of 2 — YouTube : This introduction to acids and bases discusses their general properties and explains the Arrhenius definitions for acids and bases. Originally, acids and bases were defined by Svante Arrhenius. Keep in mind that acids and bases must always react in pairs.
This is because if a compound is to behave as an acid, donating its proton, then there must necessarily be a base present to accept that proton. Lastly, note that the reaction can proceed in either the forward or the backward direction; in each case, the acid donates a proton to the base.
The products include the acetate ion, which is the conjugate base formed in the reaction, as well as hydronium ion, which is the conjugate acid formed. Note that water is amphoteric; depending on the circumstances, it can act as either an acid or a base, either donating or accepting a proton. The conjugate acid formed in the reaction is the ammonium ion, and the conjugate base formed is hydroxide.
Part 2 of 2 — YouTube : This lesson continues to describe acids and bases according to their definition. Under standard conditions, water will self-ionize to a very small extent. The self-ionization of water refers to the reaction in which a water molecule donates one of its protons to a neighboring water molecule, either in pure water or in aqueous solution.
The reaction can be written as follows:. Autoprotolysis of water : The self-ionization of water produces hydronium and hydroxide ions in solution. Like all equilibrium reactions, this reaction has an equilibrium constant. Because this is a special equilibrium constant, specific to the self-ionization of water, it is denoted K W ; it has a value of 1.
If we write out the actual equilibrium expression for K W , we get the following:. Here we have the reason why neutral water has a pH of 7. This relationship always holds true for any aqueous solution, regardless of its level of acidity or alkalinity.
Utilizing this equation is a convenient way to quickly determine pOH from pH and vice versa, as well as to determine hydroxide concentration given hydrogen concentration, or vice versa. Self-ionization of Water : Explanation of self-ionization of water and the formation of hydronium and hydroxide ions. The acid dissociation constant K a is the measure of the strength of an acid in solution. The acid dissociation constant K a is a quantitative measure of the strength of an acid in solution.
K a is the equilibrium constant for the following dissociation reaction of an acid in aqueous solution:. The K a expression is as follows:. Acid dissociation constants are most often associated with weak acids, or acids that do not completely dissociate in solution. However, in water, there is a balance between hydroniums and hydroxyls so they cancel each others' charges. Pure water is neither acidic or basic; it is neutral. So how does something become acidic or basic?
That happens when the hydroniums and the hydroxyls are out of balance. If there are more positively charged hydroniums than negatively charged hydroxyls, then the substance is acidic. If there are more negatively charged hydroxyls than positively charged hydroniums, then the substance becomes basic. Watch out for that, and ask for clarification! When we dissolve acids in water, we create an excess of hydroniums. When we dissolve bases in water, we create an excess of hydroxyls.
Here are two examples. Now let's look at lye, a strong base with the chemical formula NaOH sodium hydroxide. The sodiums don't do anything important, but the hydroxyls make the solution more basic. One last question: Why are strong acids and strong bases so nasty? It's because they are out of balance. They either have too many positive charges and are looking for negatives to get back into balance, or they have too many negative charges and are looking for positives to get back into balance.
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