3/27/2015. So the question that arises is, how can you tell the difference between an ionic solution and a solution containing a molecular acid?

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1 A neat thing about chemistry is that there are exceptions to most rules. Previously, we learned that ionic compounds form electrolytic solutions but molecular compounds do not form electrolytic solutions. However, there is one class of molecular compounds that do form conducting solutions. These compounds are known as molecular acids. Molecular acids: hydrogen compounds that dissolve in water to form conducting solutions. The molecular acids include certain hydrogen containing compounds which literally split up (dissociate) into hydrogen ions (H + ) and anions when they are dissolved in water. Acids can be simply defined as substances that release hydrogen ions (H + ) in water. Example: hydrochloric acid HCl H + (aq) + Cl - (aq) Even though this compound is made up of two non-metals (its molecular), the presence of free ions allows the solution to conduct electricity! So the question that arises is, how can you tell the difference between an ionic solution and a solution containing a molecular acid? The answer is to perform a litmus paper test. Acids turn blue litmus red. Ionic solutions remain neutral and have no effect on the color of the litmus. In order for a molecular acid to have acidic properties it must be dissolved in water. That is, the formula of an acid must be followed by the (aq) subscript. Therefore, in order to classify a substance as an acid based on its formula: it must contain H it must be dissolved in water (aq) HCl (aq) HF (aq) H 2 SO 4 (aq) H 2 CO 3 (aq) hydrochloric acid hydrofluoric acid sulfuric acid carbonic acid 1

2 When you are given a chemical formula for a hydrogen compound that has the (aq) state of matter subscript, you name it as an acid 1. name the hydrogen compound as if it were an ionic compound. (all of these compounds should end in - ide, -ate, or -ite.) 2. depending on the ending convert the ionic name to the acid name. hydrogen ide hydro ic acid hydrogen ate ic acid hydrogen ite ous acid If the aqueous hydrogen compound has the -ide ending, then: 1. drop the -gen ending of hydrogen 2. replace the -ide ending of the anion with -ic Example: HCl (aq) Hydrogen chloride hydrochloric acid If the aqueous hydrogen compound has the -ate ending, then: If the aqueous hydrogen compound has the -ite ending, then: 1. drop the name hydrogen 2. replace the -ate ending of the anion with -ic 1. drop the name hydrogen 2. replace the -ite ending of the anion with -ous Example: HClO 3 (aq) hydrogen chlorate chloric acid Example: HClO 2 (aq) hydrogen chlorite chlorous acid 1. HBr (aq) 2. HNO 3 (aq) 3. HNO 2(aq) 4. HCN (aq) 5. H 2 CrO 4 (aq) 6. HClO (aq) 1. hydrobromic acid 2. nitric acid 3. nitrous acid 4. hydrocyanic acid 5. chromic acid 6. hypochlorous acid When the acid contains sulfur or phosphorus we add syllables. sulfur add the -ur phosphorus add the -or The four cases you will use are: H 2 SO 4 (aq) sulfuric acid H 2 SO 3 (aq) sulfurous acid H 2 S (aq) hydrosulfuric acid H 3 PO 4 (aq) phosphoric acid 2

3 In these acids, the acidic hydrogen is the one on the end of the COOH. CH 3 COOH (aq) CH 3 COO - + H + 1. C 17 H 35 COOH (aq) 1. hydrogen stearate Stearic acid 2. HOOCCOOH (aq) 2. hydrogen oxalate oxalic acid both hydrogen come off! HOOCCOOH (aq) OOCCOO H + CH 3 COOH (aq) becomes hydrogen acetate which becomes acetic acid. In order to convert an acid name to a chemical formula: 1. convert the acid name to an ionic name hydro ic acid hydrogen ide ic acid hydrogen ate ous acid hydrogen ite 2. identify the two ions from the ionic name and write their symbols with their charges 3. determine the number of hydrogen ions required to cancel the negative charge on the anion 4. add the (aq) state of matter subscript to the end of the formula Write the chemical formula for hydroiodic acid: hydroiodic acid hydrogen iodide H + I - HI (aq) Write the chemical formula for boric acid: Write the chemical formula for nitrous acid: Boric acid Hydrogen borate Nitrous acid hydrogen nitrite H + BO 3 3- H + NO 2 - H 3 BO 3 (aq) HNO 2 (aq) 3

4 1. hydrofluoric acid 2. carbonic acid 3. sulfurous acid 4. hydrosulfuric acid 5. perchloric acid 6. silicic acid 1. HF (aq) 2. H 2 CO 3 (aq) 3. H 2 SO 3 (aq) 4. H 2 S (aq) 5. HClO 4 (aq) 6. H 2 SiO 3 (aq) Here are several key properties that distinguish acids from other classes of compounds: 1. acids turn blue litmus paper red 2. acids react with metals like zinc, magnesium, and iron to produce hydrogen gas. (Hydrogen gas is flammable.) 3. acids neutralize bases 4. acids have low ph (ph < 7) 5. acids that are edible, such as those found in foods, taste sour (e.g. vinegar, and citric acid found in oranges, lemons, and other citrus fruits, sour candy.) Bases are substances that behave in opposition to acids. our discussion of bases will be restricted to one type: ionic compounds that contain the hydroxide ion (OH - ). example: Sodium hydroxide NaOH (aq) turn red litmus blue neutralize acids have high ph (> 7) form slippery solutions tend to have a bitter taste The ph scale is a measure of the concentration of hydrogen ions (H+) in aqueous solution, and can be used to compare the strength of acid or base. The ph scale ranges from ph = 1 (strong acid), to ph = 14 (strong base). The value ph = 7 is neutral (neither acid nor base) 4

5 Salts are formed as a result of the reaction between an acid and a base. The reaction between an acid and a base results in the formation of salt and water. The type of salt formed would be determined by the type of acid and base that react in the neutralization reaction. ACID + BASE SALT + WATER Salts are essentially ionic compounds that produce neutral solutions. A salt does not necessarily mean sodium chloride. Consider the following reaction: ACID + BASE SALT + WATER HI (aq) + KOH (aq) KI (aq) + H 2 O Potassium Iodide: used with silver nitrate to make silver iodide (AgI) an important chemical in film photography a component in some disinfectants and hair treatment chemicals. 5