Name AP Unit 9: Acids and Bases Everything you should know already Naming Acids: Acids are named using a unique classification system. There are 3 general guidelines: If the anion ends in ide name the acid as hydro(root)ic acid If the anion ends in ate name the acid as (root)ic acid If the anion ends in ite name the acid as (root)ous acid Complete the following table: Acid Formula Anion formula Anion name Acid name HCl Cl -1 Chloride Hydro chlor ic acid HI I -1 Iodide Hydroiodic acid H2SO3 SO3 2- Sulfite Sulfurous acid H2Se Se 2- Selenide Hydroselenic acid HF F -1 fluoride Hydrofluoric acid HBr Br -1 bromide Hydrobromic acid HBrO3 BrO3-1 Bromate Bromic acid H2SO4 SO4 2- Sulfate Sulfuric acid HCN CN -1 Cyanide Hydrocyanic acid HClO ClO -1 hypochlorite Hypochlorous acid H2CO3 CO3 2- carbonate Carbonic acid Naming Bases: Bases are named just as any other ionic compound. Name the metal first, then the name of anion. Name the following compounds: Acid Formula HC 2H 3O 2 ioh HMnO4 Fe(OH) 2 HClO4 H 2Cr 2O 7 Acid Name Acetic acid ithium hydroxide Permanganic acid Iron(II) hydroxide Perchloric acid Dichromic acid
What kinds of compounds are acids and bases??? There are 3 general types of bonding that determine the type of label given to a particular compound/substance. These types are summarized below: Compound/Substance Type Bonding between atoms Particle Type Ionic Compound Ionic bonds Metal Cations and Non-metal Anions Metallic Substance Metallic bonds Metal Cations Molecular Compound Covalent bonds Molecules (non-metals only) So where do acids belong on this table? Most acids are actually molecular compounds with covalent bonds between atoms. ike other molecules, ewis structures can be drawn. Try drawing ewis structures for the simple acid molecules shown below. The rules for drawing ewis structures have been provided for reference. ewis Structures: 1. Arrange atoms symmetrically and count the total 1. HF 2. HCl number of valence electrons available for use in bonding. 2. Add single bonds between atoms. 3. Give octets to outer atoms first. 4. Extra electrons are placed on the central atom last. 5. If the central atom does not have octet, bring in lone pairs from outer atoms to make double/triple 3. H2S 4. H2O bonds. Analysis Questions: Formal Charge: FC = VE s [PE s + ½(BE s)] VE s = valence electrons the atom had PE s = lone pair electrons around the atom BE s = bonding electrons around the atom a. Evaluate the polarity of HF, HCl and H2S molecules. All are polar due to differences in electronegativity of the atoms and the asymmetrical arrangement of the polar bonds. HF is most polar however, because the difference in electronegativity between H and F is the greatest. b. Predict which molecule is more soluble in water and why. Be sure to discuss intermolecular forces in your answer. HF should be most soluble in water because it is the most polar. All of the substances are polar, so all will form dipole-dipole interactions with water molecules and be soluble. HF will form the strongest dipole-dipole forces and will therefore be the most soluble. Now try drawing ewis structures for more complex acids involving polyatomic ions. Normally, the hydrogen atoms attach to the oxygen atoms which surround the central atom, as shown in the example. Example: H2SO4 5. HNO2 6. HNO3 (2 possible resonance, 1 acceptable structure) (3 possible resonance, 2 acceptable structures)
7. H2CO3 8. H3PO4 (3 possible resonance, 1 acceptable structure) (no resonance, but be sure all FC s are 0) 9. H3PO3 10. HClO3 (no resonance) (no resonance, but be sure all FC s are 0) 11. HClO2 12. HCN (on your own) (on your own) 13. HClO 14. H2SO3 (on your own) (on your own) So where do bases belong on this table? Many bases are ionic compounds, composed of a metal cation bonded to the polyatomic ion hydroxide, OH -1. Example: sodium hydroxide, NaOH, and zinc hydroxide, Zn(OH)2 Some bases however, are actually molecules, composed of non-metal atoms bonded covalently. Draw ewis structures for the molecular bases shown below. 1. NH3, ammonia 2. CH3NH2, methyl amine
Arrhenius Definition of Acids and Bases: Acids and bases can be defined in many ways. The simplest definition is the Arrhenius version, which describes how an acid and/or a base will dissociate upon addition to water. For each of the following compounds, describe how it will dissociate in water according to Arrhenius AND label it as an acid or a base. HF H + + F - H2CrO4 2H + + CrO4-2 Al(OH)3 Al +3 + 3OH -1 H3PO4 3H + + PO4-3 Acid or base? (circle one) Acid or base? (circle one) Acid or base? (circle one) Acid Chlorous acid HClO2 H + + ClO2 - Copper(II) hydroxide Cu(OH)2 Cu +2 + 2OH -1 Hydrobromic acid HBr H + + Br -1 H3PO3 Ni(OH)2 Properties of Acid/Base solutions: For each of the following solutions, answer the questions based on the expected solution properties. 100 m of 3.00 M HCl solution a. What color change would be expected with the addition of phenolphthalein? No change b. If you were not following proper safety procedures and accidentally got some of this solution in your mouth, how would it taste? sour c. Would you expect this solution to conduct an electric current? yup 100 m of 3.00 M NaOH solution a. What color change would be expected on red litmus paper dipped in the solution? blue b. What color change would be expected with the addition of phenolphthalein? pink c. If the HCl solution was added to this solution and then the ph was checked, what would the expected ph be? A neutral ph would be expected, 7 Acidity: There are many ways that a solution s acidity or alkalinity could be evaluated, but the most common way is by analyzing the amount of H + ions that are present in the solution. Many H + ions = highly acidic Fewer H + ions = less acidic (more alkaline) A solution that is termed alkaline contains a base, rather than an acid. The amount of H + ions in solution is kept track of using Molarity, or M, or [H + ].
1. Solution A has an [H + ] = 5.4x10-3 while Solution B has [H + ]=6.7x10-13. Which solutions is more acidic? Solution A has more H + ions, so it is more acidic. 2. Solution C has an [H + ]=2x10-6 while solution D has an [H + ]=3.5x10-8. Which solutions is more acidic? Solution C has more H + ions, so it is more acidic. 3. If 500. m of solution A is measured, how many moles of hydrogen ions are present in the solution? If 500. m of solution B is measured, how many moles of hydrogen ions are present in the solution? Does this agree with your prediction about which is more acidic? M = mol 5. 4x10 3 M = mol 0.5 moles = 0.0027 M = mol 6. 7x10 13 M = mol 0.5 moles = 3. 4x10 13 4. 0.009 grams of HI is dissolved in water to produce a 750 m solution. What is the molarity of hydrogen ions present in this solution? 0. 009 g x M = moles 1mole HI 1mole H x 127.9g = 7.04x10 5 0.75 1mole HI = 7. 04x10 5 moles H = 9. 38x10 5 5. 6.6 grams of NaOH is dissolved in water to produce a 550 m solution. What is the molarity of hydroxide present in this solution? 6. 6 g x 1moleNaOH 40g M = mol x 1moleOH 1 = 0. 165 moles OH 1moleNaOH 0.165 moles = = 0. 3 M 0.55 ph Scale: ph is a number system that expresses the amount of hydrogen ions (or hydronium ions, depending on the definition) that are present in the solution. The ph scale will be discussed at great length in class, but here is a review of the basics. The ph formula will need to be used for some of the questions below. abel the following on the ph scale to the right. a. Acidic range b. Alkaline range c. Neutral d. Strong acid range e. Strong base range Strong Acidic range Neutral Alkaline range Strong 2. If a solution has an [H + ] = 1.0x10-3, what is the ph? Is it an acidic or basic solution? ph = 3 3. If a solution has an [H + ] = 1.0x10-9, what is the ph? Is it an acidic or basic solution? ph = 9 4. If a solution has a ph of 7.2, what is the [H + ]? 10 7.2 = 6. 3x10 8 M
5. According to the chart above, what is the approximate [H + ] in orange juice? 1x10 3 M 6. How many times greater is the [H + ] in pure water than in sea water? How does this help to explain the ph scale being a logarithmic scale? 10 times greater! On a logarithmic scale, every number is ten times greater than the previous. poh poh is a separate scale that is used to express the amount of hydroxide ions, OH -, present in an aqueous solution. It is found using the same formulas a ph, except with [OH - ] instead of [H + ]. A simple formula is used to interconvert between [OH - ] and the poh value: poh = -log[oh - ] If the formula reveals that a high concentration of hydroxide is present, the solution is less acidic and more alkaline. The opposite is true if a low concentration of hydroxide is present. Many OH - ions = highly alkaline Fewer OH - ions = less alkaline (more acidic) 1. If a solution has an [OH - ] = 5.1x10-3, what is the poh? Is it an acidic or basic solution? log(5. 1x10 3 ) = 2. 29 This is a basic solution because of the high OH - concentration 2. If a solution has a poh = 8.9, what is the [OH - ]? 10 8.9 = 1x10-9 3. On the poh scale below, label what range indicates an acidic solution and what range indicates a basic (alkaline) solution. Alkaline range Acidic range Acid/Base Neutralization Reactions: If equimolar amounts of acid and base react, the two compounds are both used up (both are limiting reagants) and only a salt and water remain. This reaction usually takes the form of a double replacement reaction, following the general guideline shown below. AX + BY BX + AY H2SO4 + NaOH Na2SO4 + HOH Acid Base Salt water The equation needs to be balanced to satisfy the law of conservation of mass 1 H2SO4 + 2 NaOH 1 Na2SO4 + 2 HOH
Considering that most species are aqueous, and that most acids and base ionize when dissolved in water, a net ionic equation can be written Complete equation: 1 H2SO4 (aq) + 2 NaOH (aq) 1 Na2SO4 (aq) + 2 HOH (aq) Ionic equation: 2H + (aq) + SO4-2 (aq) + 2Na + (aq) + 2OH - (aq) 2Na + (aq) + SO4-2 (aq) + 2HOH(l) Cross off spectator ions Net ionic equation: 2H + (aq) + 2OH - (aq) 2HOH(l) Write complete, balanced equations for each of the following acid-base neutralization reactions. 1. HCl (aq) + NaOH (aq) HOH (l) + NaCl(aq) 2. 2 HBr (aq) + Mg(OH)2 (aq) 2 HOH (l) + MgBr2 (aq) 3. H2SO4 (aq) + 2 ioh (aq) 2 HOH (l) + i2so4 (aq) 4. 2 H3PO4 (aq) + 3 Ca(OH)2 (aq) 6 HOH (l) + Ca3(PO4)2 (aq) Write complete, balanced net ionic equations for each of the following. 5. HI (aq) + NaOH (aq) HOH (l) + NaI (aq) Na + and I - are specators Net: H + + OH - HOH 6. 2 HNO3 (aq) + Mg(OH)2 (s) 2 HOH(l) + Mg(NO3)2 (aq) NO3 - is a spectator Net: 2 H + + Mg(OH)2 2 HOH + Mg +2 7. H2SO4 (aq) + Ca(OH)2 (s) HOH (l) + CaSO4 (s) no spectators, so that IS the net 8. H3PO3 (aq) + 3 ioh (aq) 3 HOH (l) + i3po3 (aq) i + and PO3-3 are spectators Net: H + + OH - HOH Stoichiometry with acid/base neutralization reactions: Write complete, balanced reactions before solving the following stoichiometry problems. 1. What volume of 3 M hydrochloric acid solution must be added to completely react with 100 m of 1 M NaOH solution? HCl + NaOH HOH + NaCl 3 M 1M? 0.1 M = moles 1 M NaOH = moles NaOH 0.1 0.1 moles NaOH is present 0. 1 moles NaOH x 1 mol HCl 1 mol NaOH = 0. 1 moles HCl 0.1molesHCl 3 M HCl = iters 0.033 iters HCl
2. What volume of 6 M sulfuric acid solution must be added to completely react with 100 m of 1 M lithium hydroxide solution? H2SO4 + 2 ioh i2so4 + 2 HOH (l) 6 M 1 M? 0.1 1 M = molesioh 0. 1 = 0. 1 moles ioh 1 mole H2SO4 0. 1 moles ioh x = 0. 05 moles H2SO4 2 moles ioh 6 M H2SO4 = 0.05molesH2SO4 iters iters = 0.00833 of 6 M H2SO4 3. What volume of 0.05 M potassium hydroxide solution must be added to completely react with 500 m of 0.05 M phosphoric acid solution? 3 KOH + H3PO4 K3PO4 + 3 HOH 0.05 M 0.05 M? 0.5 0. 05 M = moles H3PO4 0. 5 = 0. 025 moles H3PO4 3 moles KOH 0. 025 moles H3PO4 x = 0. 075 moles KOH 1 moles H3PO4 0. 05 M KOH = 0.075 moles KOH iters iters = 1.5 of 0.05 M KOH 4. What ions are present in solution if 100 m of 2 M hydroiodic acid solution is mixed with 300 m of 5 M sodium hydroxide solution? HI(aq) + NaOH (aq) HOH (l) + NaI (aq) 2 M 5 M 0.1 0.3 Net: H + + OH - HOH (l) 2 M 5 M 0.1 0.3 0.2 mol 1.5 mol 1mol OH Find the R: 0. 2 moles H x = 1 mole OH needed 1. 5 moles OH actually present 1mol H So OH - is in excess and H + must be the R Since H + is the R, there will be none left in solution, so the only ions present are the excess OH - and the spectators which are Na + and I -