Acids, Bases, and Salts Chapter 18

Properties of Acids and Bases When dissolved in distilled water, they look the same Taste –Acid developed from the latin term acidus (sour or tart) Citric acid, lactic acid, carbonic acid, hydrochloric –Bases taste bitter Soap is an example of a base

Properties of Acids and Bases Touch –Dilute acids do not cause painful burns, but if an open wound is exposed, then a sting is felt –Dilute bases do not sting (except in eyes) Typically feel smooth or soothing in low concentrations –The higher the concentration for either acids or bases can result in painful burns

Properties of Acids and Bases Reactions with Metals –Acids react with several metals including Mg, Zn, Fe, Al See activity series p. 295 –Bases do not react with metals

Properties of Acids and Bases Electrical Conductivity –Both acids and bases are good electrolytes (good conductors of electricity) –Distilled water is a poor conductor, but if an acidic or basic solution is made, then the solution is quite conductive –Electrolyte = substance that ionizes when dissolved in water

Properties of Acids and Bases Indicator = substance that turns 1 color in an acidic solution and a different color in a basic solution Litmus is the most common indicator. –Acids turn blue litmus paper RED or PINK –Bases turn red litmus paper BLUE Phenolphthalein is another example which changes colors at a specific level of acidity or basicity

Properties of Acids and Bases Neutralization Reaction = reaction between an acid and a base –If the proper amounts of acid and base are added, they will completely neutralize each other. Based on MOLES –Two products are always formed H 2 O and an ionic salt

Arrhenius Definition Swedish chemist Svante Arrhenius Developed an operating definition of acids and bases according to the ions they produce when dissolved in water –Acids – dissociate in water to produce hydrogen (H + ions) HCl, HNO 3, H 2 SO 4 –Bases – dissociate in water to produce hydroxide (OH - ions) NaOH, Ca(OH) 2

Dissociation Examples Mg(OH) 2 (aq)  HBr (aq)  HC 2 H 3 O 2 (aq)  CuOH (aq) 

Neutralization examples NaOH (aq) + HCl (aq)  Mg(OH) 2 (aq) + HBr (aq)  HC 2 H 3 O 2 (aq) + CuOH (aq) 

Arrhenius Definition Limitations Restricts acids and bases to water solutions –Acid and base reactions can occur in the gas phase or can be dissolved in other solvents Chemicals such as ammonia (NH 3 ) are bases, yet they do not have an OH - in the formula. So, a new “definition” had to be developed

Bronsted-Lowry Definition Acid – substance that can donate H + ions Base – substance that can accept H + ions What is an H + ion? How many protons, neutrons, and electrons? So…H + can also be referred to as a ____. Acid – substance that can donate _____. Base – substance that can accept ____.

Polyprotic? Protic refers to “protons” How many protons does a monoprotic acid donate? How many protons does a diprotic acid donate? H 3 PO 4 is an example of a _____ acid.

Hydronium Ions H + ions are very attracted to the electrons of surrounding water molecules. H + + H 2 O  H 3 O + H 3 O + = hydronium ion

ID the B-L Acids and Bases HCl (g) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) NH 3 (g) + H 2 O (l)  NH 4 + (aq) + OH - (aq)

Amphoterism A substance that can act as an acid or a base depending on the circumstances. See previous slide.

Conjugate Acid-Base pairs Technically, almost all acid-base reactions are reversible NH 3 (g) + H 2 O (l) NH 4 + (aq) + OH - (aq) Conjugate means coupled or joined “Conjugate” is used to describe the acid or base in the reverse reaction.

Determining the Strengths of Acids and Bases Vinegar contains 1M acetic acid –Spilling this on your skin has no great effect –Spilling 1 M HCl on your skin is a cause for concern –Why? The strength of an acid or base is dependent upon the degree to which they dissociate.

Strong vs Weak HCl is a strong acid…so it is assumed that it dissociates completely HCl (g) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) lots lots Acetic acid is a weak acid…so not very much product is produced…it is reversible HC 2 H 3 O 2 (aq) + H 2 O (l) H 3 O + (aq) + C 2 H 3 O 2 - (aq) little little

Strong and Weak Acids Strong Acids HCl HBr HI HNO 3 H 2 SO 4 Weak Acids HC 2 H 3 O 2 HCN HNO 2 HF H 2 CO 3

Strong and Weak Bases Strong Bases CaO NaOH KOH Ca(OH) 2 Weak Bases NH 3 CO 3 2- PO 4 3-

Acid Dissociation Constant Generic Weak Acid, formula = HA HA (aq) + H 2 O (l) H 3 O + (aq) + A - (aq) How would the Keq be written? We also call this K a, or the acid dissociation constant. What does a large K a mean? Small K a ?

Base Dissociation Constant Generic base, formula = B B (aq) + H 2 O (l) HB + (aq) + OH - (aq) How would the Keq be written? We also call this the K b, or the base dissociation constant. What does a large K b mean? Small K b ?

Identifying Acids Binary Acids Contain hydrogen and one other element (usually group 6A or 7A) HCl HF H 2 Se H 2 S Ternary Acids (Oxyacids) Contain hydrogen, oxygen, and one other element H 2 SO 4 HNO 3 H 3 PO 4

Identifying Bases Most of the bases we will work with will have the OH - ion in the formula. NaOH Mg(OH) 2 Otherwise you should recognize ammonia (NH 3 ) as a base even though it does not have an OH in the formula.

Naming Acids Typically, the name of the acid comes from the name of the ion it produces when it dissociates. Rule 1: If the name of an anion ends in -ide, the name of the acid that produces it includes the name of the anion, a hydro- prefix, and an –ic ending. Cl - is the chloride ion. The acid which produces it is HCl. Hydro- is placed in front, chlor is the root, and –ic is the ending. Hydro + chlor + ic acid = hydrochloric acid

Naming Acids Rule 2: If the name of an anion ends in – ate, the name of the acid that produces this anion has NO prefix (no hydro), but it does have an –ic ending. NO 3 - is nitrate. Nitr is the root and –ic is the ending. Nitr + ic acid = nitric acid

Naming Acids Rule 3: If the name of an anion ends in – ite, the name of the acid that produces this anion has NO prefix and has an –ous ending. SO 3 2- is the sulfite ion. Sulf is the root and –ous is the ending. Sulfur + ous = Sulfurous acid Note…sulfurous, not sulfic…

Bases Name them just like all ionic compounds NaOH = sodium hydroxide Ca(OH) 2 = calcium hydroxide Mg(OH) 2 = Cu(OH) = Cu(OH) 2 =

Try these acids Name Phosphoric acid Nitrous acid Hydrofluoric acid Chloric acid Formula H 2 CO 3 H 2 Se HIO 4