Chemically what makes an acid

OH - is called a hydroxyl ion and it makes things basic. 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. 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. This is because strong acids are presumed to ionize completely in solution and therefore their K a values are exceedingly large.

Due to the many orders of magnitude spanned by K a values, a logarithmic measure of the acid dissociation constant is more commonly used in practice. The logarithmic constant pK a is equal to -log 10 K a. The larger the value of pK a , the smaller the extent of dissociation. A weak acid has a pK a value in the approximate range of -2 to 12 in water. Acids with a pK a value of less than about -2 are said to be strong acids. A strong acid is almost completely dissociated in aqueous solution; it is dissociated to the extent that the concentration of the undissociated acid becomes undetectable.

Acetic acid dissociation : The acetic acid partially and reversibly dissociates into acetate and hydrogen ions. What is the pK a for acetic acid? This reaction has a special equilibrium constant denoted K W , and it can be written as follows:. Here we have the reason that neutral water has a pH of 7. This relationship will always apply to aqueous solutions. It is a quick and convenient way to find pH from pOH, hydrogen ion concentration from hydroxide ion concentration, and more.

The pH and pOH Scale : Relation between p[OH] and p[H] brighter red is more acidic, which is the lower numbers for the pH scale and higher numbers for the pOH scale; brighter blue is more basic, which is the higher numbers for the pH scale and lower numbers for the pOH scale.

Generically, this p-notation can be used for other scales. However, because these values are often very small for weak acids and weak bases, the p-scale is used to simplify these numbers and make them more convenient to work with. Quite often we will see the notation pK a or pK b , which refers to the negative logarithms of K a or K b , respectively. Interactive: pH : Test the pH of things like coffee, spit, and soap to determine whether each is acidic, basic, or neutral.

Visualize the relative number of hydroxide ions and hydronium ions in solution. Scientists sometimes use another scheme — the Lewis system — to define acids and bases. Instead of protons, this Lewis definition describes what molecules do with their electrons. Lewis acids only need to be able to accept electron pairs.

Different definitions are useful for different situations, explains Jennifer Roizen. She is a chemist at Duke University in Durham, N.

Water H 2 O is chemically neutral. That means it is neither an acid nor a base. But mix an acid with water and the water molecules will act as bases. Mix water with a base and that water will play the part of the acid. Now the water molecules give up their own protons to the base and become what are known as hydroxide Hy-DROX-ide molecules. To identify acids from bases, and the relative strength of each, chemists tend to use a pH scale. Seven is neutral. Anything with a pH below 7 is acidic.