Waves and Sound - Loudoun County Public Schools



UNIT 13Acids, Bases and SaltsArrhenius definition of acids and bases:Acid: a chemical compound that increases the concentration of hydrogen ions (H+) in aqueous solutionHCl (aq) → H+ (aq) + Cl- (aq)Base: a substance that increases the concentration of hydroxide ions (OH-) in aqueous solutionNaOH (aq) → Na+ (aq) + OH- (aq)Properties of AcidsProperties of Bases Acids:Bases:HCl + H2O ? H3O+ + Cl-NaOH + H2O → Na+ + OH-feel slippery? taste sourtaste bitter? corrosivecorrosive? electrolytes (strong)electrolytes (strong)? react with indicators to change colorreact with indicators to change colorCommon acids Common bases Four most important industrial acids:1 – ammonia - most widely used1 - sulfuric acidNH3 + H2O → NH4+ + OH- → NH4OHformula: H2SO4formula: NH3uses: car batteriesuses: clenaers, rayon/nylonproduction2 - phosphoric acid2 - calcium hydroxide - “caustic lime” formula: H3PO4formula: Ca(OH)2uses: detergentsuses: mortar, plaster3 - nitric acid3 – sodium hydroxide – “lye”formula: HNO3formula: NaOHuses: fertilizer, explosives (TNT)uses: soap, drain cleaner4 – hydrochloric acid (muriatic acid)formula: HCluses: cleaner, gastric juicesBr?nsted- Lowry definition of acids and bases:Acid: proton (H+) donorBase: proton (H+) acceptorLabel the parts of the general reaction for a Br?nsted- Lowry acid and water:HA (aq) + H2O (l) ? H3O+ (aq) + A- (aq) acid base conj acid conj baseConjugate Base: Everything that remains of the acid molecule after a proton (H+) is lost.Conjugate Acid: The base with the transferred proton (H+).Conjugate Acid/Base Pair: two substances related to each other by the donating and accepting of a single proton.Example: Finish each equation and identify each member of the conjugate acid/base pair.H2SO4 (aq) + H2O (l) ? HSO4- + H3O+ acid base conj base conj acidCO32- (aq) + H2O (l) ? HCO3- + OH-base acid conj acid conj baseThe hydronium ion, H3O+, forms when water behaves as a base.(The two unshared pair of electron on the O bond covalently with the H+)Example: Write the conjugate base for each of the following:HClO4 → ClO4-H3PO4 → H2PO4-CH3NH3+ → CH3NH2 Diprotic Acid: an acid that can provide two protonsH2SO4 (aq) → HSO4-HSO4-(aq) → SO42-Water as an Acid and a BaseAmphoteric: a substance that can behave as either an acid or a base (water is the most common)Ionization of water:H2O (l) + H2O (l) ? H3O+(aq) + OH-(aq)In the shorthand form:H2O (l) ? H+(aq) + OH-(aq)There are three possible situations:A neutral solution where [H+] = [OH-] An acidic solution where [H+] > [OH-] A basic solution where [H+] < [OH-] Ion-product constant: Kw refers to the ionization of waterKw = [H+] [OH-]At 25 ?C, Kw = [H+] [OH-] = [1.0 x 10-7] [1.0 x 10-7] = 1.0 x 10-14If [H+] increases, [OH-] decreases, two the product of the two is still 1.0 x 10-14Example:Calculate [H+] or [OH-] as required for each of the following at 25 ?C.For each solution state whether it is neutral, acidic or basic. 1.0 x 10-5 M OH-2) 1.0 x 10-7 M OH-3) 10.0 M H+ 1.0 x 10-9 M H+ 1.0 x 10-7 M H+ 1.0 x 10-15 M OH- basic neutral acidicpH scale – because the [H+] in an aqueous solution is typically small, logarithms are used to express solution acidity.Mental math: calculating pH:substanceconcentration (M)pHacid, base or neutral?[H3O+]1 x 10-99base[H3O+]1 x 10-66acid[H3O+]1 x 10-22acid[H3O+]1 x 10-1111base[H3O+]1 x 10-77neutral[OH-]1 x 10-9 (pOH = 9)5acid[OH-]1 x 10-6 (pOH = 6)8base[OH-]1 x 10-2 (pOH = 2)12base[OH-]1 x 10-11 (pOH = 11)3acid[OH-]1 x 10-7 (pOH = 7)7neutralpH = -log [H+]pOH = -log [OH-]pH = -log [H+]pOH = -log [OH-]graphing calculator steps:Press the +/- keyPress the log keyEnter the [H+]Significant figure rule for pH: the number of places to the right of the decimal for a log must be equal to the number of significant figures in the original number. [H+] = 10-pH [OH-] = 10-pOHgraphing calculator steps:Press 2nd function, then logPress the +/- keyEnter the pHSince Kw = 1.0 x 10-14, pH + pOH = 14Fill in the missing information in the table below:pH[H3O+] or [H+]pOH[OH-]Acid or Base?3.166.92 x 10-410.841.45 x 10-11Acid.9791.05 10-1 M13.09.52 x 10-14Acid10.285.25 x 10-113.721.91 x 10-4Base7.881.30 x 10-86.127.53 x 10-7 MBase7.951.12 x 10-86.058.91 x 10-7Base9.324.72 x 10-10 M4.672.12 x 10-5Base2.672.14 x 10-311.334.68 x 10-12Acid12.01.02 x 10-122.019.77 x 10-3 MBase10.682.09 x 10-113.324.79 x 10-4Base7.039.23 x 10-8 M6.971.08 x 10-7BaseNeutralizationReaction of an acid and a base will always produce water and “a salt,” as shown belowacidbasewatersaltHCl+NaOH→HOH+NaClHBr+KOH→HOH+KBrWhen equal amounts of an acid and a base react, there is an exact neutralization with no remaining H+ or OH-. We can use the equation below to determine how much of an acid or a base is needed to completely neutralize an acid or a base.Macid Vacid = Mbase VbaseExample: What volume of 0.30 M HCl solution is needed to completely react with 1.2 L of 0.85 M NaOH?Macid Vacid = Mbase Vbase(0.30) V = (0.85) (1.2)V = 3.4 L Neutralization with multiprotic acidsH2SO4 is a diprotic (2 protons) acid. If you have 4.0 M H2SO4 solution, what would be the [H+] in the acidic solution?H3PO4 is a triprotic (3 protons) acid. If you have 2.0 M H3PO4 solution, what would be the [H+] in the acidic solution?Example: What volume of a 0.075 M KOH solution is required to react with 0.135 L of 0.45 M H3PO4?Macid Vacid = Mbase Vbase(0.45) (0.135) = (0.075) VV = 0.81 L TitrationExperimentally, we will find the amount of acid in a solution by determining how many moles of base are required to neutralize it.Use the neutralization formula: Ma Va = Mb VbExample: The total acidity in water samples can be determined by titration with a standard sodium hydroxide solution. What is the total concentration of hydrogen ion, H+, present in awater sample of 100. mL if the sample requires 7.2 mL of 2.5 x 10-3 M NaOH to be neutralized?438839256013Macid Vacid = Mbase VbaseM (100) = (2.5 x 10-3) (7.2)M = 1.8 x 10-4 M 0Macid Vacid = Mbase VbaseM (100) = (2.5 x 10-3) (7.2)M = 1.8 x 10-4 M IndicatorsThe most common method to get an idea about the pH of solution is to use an acid base indicatorIndicator: organic molecule that has a different color at different pHsLitmus paper: red below 4.5 and blue above 8.2. Blue LitmusRed LitmusAcidturn redstay redBasestay blueturn bluebase = blueOther commercial pH papers are able to give colors for every main pH unit.Universal indicator is a mixture of indicators that is able to provide a full range of colors for the pH scale pH curveDuring an acid-base titration, the pH changes in a characteristic way. A pH curve is found by plotting the pH of the solution being titrated against the volume of solution added.The equivalence point is the point at which equivalent molar amounts of acid [H+] and base [OH-] have been mixed. When a strong bases is mixed with a strong acid, the equivalence point is right around pH = 7.An indicator (phenolphthalein) is often used in a titration to visually show when the equivalence point is reached. Choose an indicator that changes color near the equivalence pointExamples: At what pH are the equivalence points in the pH curves shown above? 7From the list provided, which is the best indicator for giving a color change at the equivalence point? phenolphthalein, phenol red, bromothymol blueStrength of acids and bases:Strong Acid: acid that ionizes almost completely in solution (electrolytes)HCl(g) + H2O(l) → H3O+(aq) + Cl- (aq)Weak Acid: acid that partially ionizes in solution (weak -non electrolytes)CH3COOH(l) + H2O(l) ? H3O+(aq) + Cl- (aq)Strong Base: dissociates completely in solution (alkaline)NaOH + H2O(l) → Na+(aq) + OH-(aq)Weak Base: partly dissociates in solutionNH3(g) + H2O(l) ? NH4+(aq) + OH- (aq)StrengthAcidBaseStrongHCl, H2SO4, HNO3, HClO4, HBr, HINaOH, KOH, LiOH, Ca(OH)2, Ba(OH)2WeakCH3COOH, H2CO3, H3BO3NH3, Al(OH)3, Fe(OH)3ChemistryName:________________________Acids and Bases WorksheetDate:__________________Water is amphoteric. What does this mean? act as acid or baseUse this equation for questions 1-4:HNO3 + H2O → H3O+ + NO3-The acid is: HNO3The base is: HOHThe conjugate acid is: H3O+The conjugate base is: NO3-Use this equation for questions 5-8:H2PO4- + H2O → H3PO4 + OH-The acid is: HOHThe base is: H2PO4-The conjugate acid is: H3PO4The conjugate base is: OH-In the reaction below, label the acid, base, conjugate acid and conjugate base:HCl + H2O → H3O+ + Cl- A B CA CBIn the reaction below, label the acid, base, conjugate acid and conjugate base:NH3 + H2O → NH4+ + OH- B A CA CBName 3 properties of acids: taste sour, corrosive, electrolytes (strong), react with indicators to produce color changeName 3 properties of bases: feel slippery, taste bitter, corrosive, electrolytes (strong), react with indicators to produce color changeWhat is the equation for expressing pH? pOH?pH = -log [H+]pOH = -log [OH-]What is the pH of 0.75 M hydrochloric acid solution?pH = 0.125What is the pH of 0.001 M barium hydroxide solution?pH = 11.30Find the pH of a strong base that has a [OH-] of 1.0 x 10-9 M.pH = 5What is the pOH if the pH is 12.05?pH = 1.95A solution has a pH of 8.5. What is the pOH?pOH = 5.5Describe strong acids and strong plete dissociation (electrolytes)Determine the conjugate acid for each: bases accept H+H2O H3O+h.F- HFHCO3- H2CO3i.SO42- HSO4- OH- H2Oj. PO43- HPO42-H2PO4- H3PO4k. Cl- HClClO4- HClO4l. CH3COO - CH3COOHSH- H2Sm. CN- HCNHSO4- H2SO4n. NH3 NH4+ Determine the conjugate base for each: acids donate H+H2O OH-h.HF F-HCO3- CO32-i.HSO4- SO42-OH- O2-j. HPO42- PO43- H3PO4 H2PO4-k. HCl Cl-HBrO2 BrO2-l. CH3COO H CH3COO-H2S HS-m. HOCN OCN-HSO4- SO42-n. NH3 NH2-Given the following reactions. Label the acid and base and draw an arrow between the conjugates. You may remove spectator ions and simply write the net ionic reaction.a. HCO3- + H2O → H3O+ + CO32- acid base CACBb. HCl + H2O → H3O+ + Cl- acid base CACBc. CH3CO2H + NaOH- → NaCH3CO2- + H2O acid base CB CAd. NH4+Cl + NaH2PO4- → NH3 + H3PO4 + NaCl acid base CB CA ................
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