A special property of acids and bases is their ability to neutralize the other's properties. Another product of a neutralization reaction is an ionic compound called a salt. Therefore, the general form of an acid-base reaction is:. Titrations are performed with acids and bases to determine their concentrations. At the equivalence point, the number of moles of the acid will equal the number of moles of the base. This indicates that the reaction has been neutralized.
For instance, 30 mL of 1. The concentration of HCl needs to be determined. At the eqivalence point:. Solution : There are 6 strong acids and all other acids are considered weak. HNO 3 is one of those 6 strong acids, while NH 3 is actuallly a weak base. They all give away protons. In the case of HPO 4 2- , consider the following equation:. Now consider the following equation:. Thus, HPO 4 2 - is an acid and base together, making it amphoteric.
A 50 ml solution of 0. What was the concentration of the HCl? Solution: Since the number of moles of acid equals the number of moles of base at neutralization, the following equation is used to solve for the molarity of HCl:.
In the following acid-base neutralization, 2. First, the number of moles of the acid needs to be calculated. This is done by using the molar mass of HBr to convert 2. Since this is a neutralization reaction, the number of moles of the acid HBr equals the number of moles of the base NaOH at neutralization:. The molarity of NaOH can now be determined since the amount of moles are found and the volume is given.
Convert However, NH 3 does not dissociate in water like the others. Instead, it takes a proton from water and becomes NH 4 while water becomes a hydroxide. Jim Clark Chemguide.
The Arrhenius Theory of Acids and Bases In , the Swedish chemist Svante Arrhenius proposed two specific classifications of compounds; acids and bases. Note Arrhenius acids are substances which produce hydrogen ions in solution. Arrhenius bases are substances which produce hydroxide ions in solution.
Limitations to the Arrhenius Theory The Arrhenius theory has many more limitations than the other two theories. In this theory, acids are defined as proton donors ; whereas bases are defined as proton acceptors. Figure 4. The pH scale shows that substances with a pH greater than 7 are basic and a pH less than 7 are acidic.
Lewis Theory The Lewis theory of acids and bases states that acids act as electron pair acceptors and bases act as electron pair doners. Figure 2. The Lewis structures of ammonia and boron trifluoride. Figure 3. A base is a substance that releases hydroxyl ions OH - when in solution. Acids, bases and salts, dissociate separate into electrolytes ions when placed in water. Every molecule of a strong base dissociates, producing a high concentration of OH —. Study Questions Write your answer in a sentence form do not answer using loose words.
The higher the pH, the less hydrogen ions the solution has. What is pH? What is a neutral solution? What is an acidic solution?
What is a basic or alkaline solution? 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.
Switch between logarithmic and linear scales. Investigate whether changing the volume or diluting with water affects the pH. Or you can design your own liquid! Privacy Policy. Skip to main content. Acids and Bases.
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