Solubility Rules. Electrolytes, Weak and Strong. Examples. Another Example:

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1 Electrolytes, Weak and Strong Electrolytes are compounds that ionize in water to produce aqueous solutions that conduct an electric current. Nonelectrolytes are substances that do not ionize, remain as molecules, and do not conduct an electric current. Strong electrolytes are molecules that ionize 100% (or nearly so) and conduct an electric current well. Weak electrolytes barely or partially ionize; most molecules remaining unionized, and conduct an electric current poorly. Examples Nitric acid (HN 3 ) is a strong electrolyte. HN 3 H +1 + N 3 If 1.00 mole of HN 3 is dissolved in water, it will ionize to produce 1.00 mole of H +1 and 1.00 mole of N 3. There will not be any HN 3 left, unionized. By contrast, one mole of a weak electrolyte will produce much less than 1.00 mole of its constituent ions. ne mole of acetic acid HC 2 H 3 2 H +1 + C 2 H 3 2 might produce 0.05 moles of H +1 and 0.05 moles of C 2 H 3 2 and still contain 0.95 moles of the original acetic acid. Another Example: Calculate the concentrations of ions in a M Ba(H) 2 solution. Ba(H) 2 is a strong electrolyte. Hint: What is the valency of Ba? What ion will it form? Where will the extra electrons go? Solubility Rules Soluble Compounds Sodium, potassium, and ammonium compounds Acetates and nitrates Halides (chlorides, bromides, and iodides) Sulfates Exceptions Lead(II), silver, and mercury(i) halides are insoluble Calcium, strontium, barium, and lead(ii) sulfates are insoluble 1

2 Insoluble Compounds Carbonates and phosphates Hydroxides Sulfides Exceptions Solubility Rules Sodium, potassium, and ammonium carbonates and phosphates are soluble Alkali hydroxides and barium hydroxide is soluble whereas strontium and calcium hydroxide are slightly soluble Sodium, potassium, calcium, and ammonium sulfides are soluble Precipitation is the pposite to Dissolution Whenever the concentration of a substance in solution exceeds its solubility, precipitation occurs. Can cause precipitation of a solution by remove solvent add solute change solvent change temperature Acids and Bases Three main definitions for acids and bases: After Arrhenius After Lewis After BronstedLowry Arrhenius Acids and Bases Autoionization or selfdissociation of water is an intrinsic property and cannot be suppressed Arrhenius Acids and Bases An Arrhenius Acid is a substance that, when dissolved in water, delivers hydrogen ions H + (aq) to the solution, i.e., it increases the concentration of hydrogen ions. HCl(g) H + (aq) + Cl (aq) An Arrhenius Base is a substance that, when dissolved in water, delivers hydroxide ions H (aq) to the solution, i.e., it increases the concentration of hydroxide ions. NaH(s) Na + (aq) + H (aq) 2

3 Hence Water is both, an Arrhenius Acid and an Arrhenius Base! Such a substance that acts as both acid and base is called amphoteric. In pure water, the concentration of hydroxide ion equals the concentration of hydrogen ion so that [H (aq)] = [H + (aq)] The Neutralization Reaction is the reaction between an acid excess H + (aq) and a base excess H (aq) leading to the formation of neutral H 2 and a salt that can either precipitate or stay in solution depending on its solubility. HCl(aq) + NaH(aq) H + (aq) + Cl (aq) + Na + (aq) + H (aq) Net: NaCl(aq) + + Cl (aq) + Na + (aq) Acids Monoprotic Acids HCl(g) H + (aq) + Cl (aq) HN 3 (g) H + (aq) + N 3 (aq) Diprotic Acids H 2 S H + (aq) + HS 4 (aq) HS 4 (aq) H + (aq) + S Triprotic Acids H 3 P 4 (l) H 2 P 4 (aq) HP H + (aq) + H 2 P 4 (aq) H + (aq) + HP H + (aq) + P 3 A binary acid is formed by hydrogen with a second element. For binary acids use the prefix hydro, attach it to the name of the element, and end with ic. Examples: HF hydrofluoric acid HCl hydrochloric acid f course, these also have names as covalent compounds 3

4 An oxoacid is formed by hydrogen with an oxoanion. For oxoacids, if the oxoanion ends in ate, replace ate with ic and add the word acid. If the oxoanion ends in ite, replace ite with ous, and add the word acid. The prefix per (meaning largest number of oxygen atoms in the oxoacid) and hypo (meaning smallest number of oxygen atoms in the oxoacid) is used when more than one possibility exists. Examples: hypochorite anion H hypochlorous acid 2 chlorite anion H 2 chlorous acid 3 chlorate anion H 3 chloric acid 4 perchlorate anion H 4 perchloric acid S 3 sulfite anion H 2 S 3 sulfurous acid S 4 sulfate anion H 2 S 4 sulfuric acid An organic acid has one or more CH groups. The naming is not systematic but involves the ate anion becoming the ic acid. Examples follow: HC formate anion HCH formic acid CH 3 C acetate anion CH 3 CH acetic acid CH 3 CHHC lactate anion CH 3 CHHCH lactic acid R C R C + H + H Strong acids Dissociate virtually completely HCl HN 3 H 2 S 4 H 4 Discuss H 2 S 4 in more detail. Weak acids Produce H + in aqueous solution to limited extent HF CH 3 CH (acetic acid) HCH (formic acid) 4

5 Typical Bases Strong bases Easily soluble in water NaH KH Ba(H) 2 Weak bases Dissolve only slightly in water but can neutralize acids Mg(H) 2, NH 3 Mg(H) 2 + HCl(aq) + MgCl 2 (aq) 5