Acids and Bases. There are a number of definitions of acids and bases we will use two of the most useful definitions for nursing applications.

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1 Acids and Bases We all know that acids taste sour and bases taste bitter but is this definition useful when you as a nurse will need to determine if a patient is in acidosis? There are a number of definitions of acids and bases we will use two of the most useful definitions for nursing applications. Each theory defines an acid or base using different characteristics. Each theory broadens the definition to include a wider range of substances. Definition #1. The Arrhenius Theory: Acid - produces hydrogen ions, H + in water solution. The positive part of a Arrhenius acid is hydrogen. Examples of Arrhenius acids: HCl, HNO 3, H 2 SO 4 Base - produces hydroxide ions, OH in water solution. The negative part of a Arrhenius base is hydroxide. Examples of Arrhenius bases: NaOH, Ba(OH) 2, Al(OH) 3 Arrhenius acids and bases are electrolytes. When each dissolves, electricity-conducting ions are released. Definition #2. The Bronsted - Lowry Theory: Acid - proton donor. In an equation, a Bronsted - Lowry acid musthave hydrogen in its formula. Base - proton acceptor. A Bronsted - Lowry base is hard to generalize for all equations. It may be a negative ion. You may have to look at the products. Find one that contains hydrogen. If the negative part of this product was in a reactant that did not contain hydrogen, that reactant is most likely the base. The Bronsted - Lowry Theory focuses on the action of protons in reactions. Since protons are in the nucleus of an atom, the hydrogen ion (H + ) is the only source of protons in a normal chemical reaction. B-L broadens the definition of acids and bases. Although hydrogen is required to produce the proton, no specific ions must be formed.

2 Depending on the circumstances, WATER can act as either a B-L Acid or Base! Example: water with a strong hydride. NH 2 + H 2 O NH 3 + OH Example: water with a strong acid. HCl + H 2 O Cl + H 3 O + Three important terms are associated with the Bronsted - Lowry (B-L) Theory: Conjugate base - the particle that remains after an acid gives up a proton. Conjugate acid - the particle formed when a base accepts a proton. Remove a proton (H + ) from a B-L acid to get its conjugate base. Add a proton (H + ) to a B-L base to get its conjugate acid. Conjugate bases and conjugate acids are ALWAYS found on the reactant side of a chemical equation. Examples: 1. HCl + H 2 O Cl + H 3 O + HCl is the B-L acid... Cl is its conjugate base H 2 O is the B-L base... H 3 O + is its conjugate acid 2. CO HS HCO 3 + S 2 HS is the B-L acid... S 2 is its conjugate base CO 2 3 is the B-L base... HCO 3 is its conjugate acid Hydronium ion - formed by a hydrogen ion and a water molecule - H 3 O + Naming Acids: Since a hydrogen ion is nothing more than a proton (a bare positive charge), when formed, this proton is immediately attracted to a polar water molecule forming a hydronium ion. Hydrogen ions never actually exist in water solution. Binary acids contain two elements - hydrogen and a nonmetal. Naming binary acids: 1. Begin with the prefix hydro-. 2. Write the stem, a part of the name of the nonmetal. 3. Add the suffix -ic. Examples of binary acids: HCl - hydro chlor ic - hydrochloric acid HBr - hydro brom ic - hydrobromic acid

3 Ternary acids contain three elements - hydrogen, oxygen, and another element. Naming ternary acids: Write the stem, a part of the name of the third element. The most common acid is given the suffix -ic. Add the prefix per- for the acid with one more oxygen. The suffix -ous is given to the acid with one less oxygen. Add the prefix hypo- for the acid with two less oxygen atoms. Examples of ternary acids: HClO 4 - per chlor ic - perchloric acid - one more oxygen. HClO 3 - chlor ic - chloric acid - most common form. HClO 2 - chlor ous - chlorous acid - one less oxygen. HClO - hypo chlor ous - hypochlorous acid - two less oxygens. Strong acids and bases ionize completely in water solution. This rule-of-thumb can be used in our class: HCl, HBr, and HI are the only strong binary acids. In strong ternary acids, the number of oxygen atoms exceeds the number of hydrogen atoms by two or more. Examples are H 2 SO 4 and HNO 3 Hydroxides of groups 1 and 2, except Be, are strong bases. Chemists define the "strength" of acids and bases by their ionization, NOT by how corrosive they are. Hydrofluoric acid is one of the most corrosive of all substances, but is considered a "weak" acid because it does not ionize completely. Weak acids and bases ionize only slightly in water solution. This rule-of-thumb can be used: Any binary acid not listed above is weak. A ternary acid is weak if the ratio of oxygen to hydrogen is less than two to one. Example: H 3 PO 4 is weak, but H 2 PO 4 is strong. Any hydroxide not listed above is a weak base. An important term related to acids: Amphoteric - a substance that acts as either acid or base, depending on what it reacts with. Water is the most common amphoteric substance. In the presence of a proton donor, it acts like a base. In the presence of a proton acceptor, it acts like an acid. This means that water is a most important component is regulating blood acidity!

4 ph a measure of the hydronium ion concentration, [H 3 O + ], in solution. The brackets, [ ], represent concentration in moles per cubic decimeter (dm 3 ), or Molarity of the ion in solution. Water ionizes according to the equation: 2H 2 O (l) H 3 O + (aq) + OH (aq) This important process is known as the auto-ionization of water. The ion product constant of water: K w = [H 3 O + ] [OH ] = 1 X This provides the basis for the ph scale. Calculating ph: The equation is: ph = log [H 3 O + ] [H 3 O + ] is expressed in powers of 10 from to 10 0 If [H 3 O + ] = 1 X 10 7, the negative log of [H 3 O + ] = 7. A ph of 7 indicates a neutral solution. ph calculations always give numbers between 0 and 14. Sample ph Calculations: 1. What is the ph of a solution with a [H 3 O + ] of 1.00 X 10 4 M? ph = log [H 3 O + ] ph = log (1 X 10 4 ) Do the following on your calculator: 1. Enter 1 X Press " LOG " (Some calculators reverse steps 1 and 2) 3. Press " + /- " or "( )" ph = 4 Tip: when the integer of the scientific notation is 1, the ph is the exponent of 10 as a positive number.

5 2. Find the ph of a solution whose [H 3 O + ] is 9.5 X 10 8 ph = log [H 3 O + ] ph = log (9.5 X 10 8 ) ph = (log log 10 8 ) ph = (.98 + ( 8)) ph = ( 7.02) ph = Calculate the [H 3 O + ] of a solution with a ph of ph = log [H 3 O + ] ph = log [H 3 O + ] 3.70 = log [H 3 O + ] antilog 3.70 = [H 3 O + ] Do the following on your calculator: Enter 3.70 antilog is usually "INV", "shift", or "2 nd " + "log" on a calculator. Now is the time to find out which of these it is on your calculator. [H 3 O + ] = 2 X 10 4 M Neutralization Reactions or Acid/Base Reactions Special types of double displacement reactions that involve the reaction between an acid and base to form a salt and water. acid + base salt + water Heat is usually given off in neutralization reactions. A suspension of solid magnesium hydroxide in water is widely used as an antacid to neutralize excess stomach acid: Mg(OH) 2 (s) + 2HCl (aq) MgCl 2 (aq) + 2H 2 O (l) Buffer Systems: solutions that can absorb moderate amounts of acid or base without a significant change in ph. Buffers provide ions that react with H 3 O + or OH, if they are introduced into the solution. As either ion is neutralized, the ph of the system remains nearly constant. Buffer solutions are prepared using a weak acid or base with one of its salts. The weak acid or base reacts with one of the added ions, the salt reacts with the other ion. The combination keeps the ph constant - up to a point. By choosing the correct weak acid or base, a buffer solution can be prepared that will maintain almost any ph.