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Kesetimbangan ion dalam Asam dan Basa. Senyawa paling banyak diproduksi. Sulfuric acid = H 2 SO 4 = Asam sulfat Hydrochloric acid = HCl = Asam Klorida Nitric acid = HNO 3 = Asam Nitrat Sodium Hydroxide = NaOH = Basa Natrium hidroksida
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Senyawa paling banyakdiproduksi • Sulfuric acid = H2SO4 = Asamsulfat • Hydrochloric acid = HCl = AsamKlorida • Nitric acid = HNO3 = AsamNitrat • Sodium Hydroxide = NaOH = BasaNatriumhidroksida • Calcium hydroxide = Ca(OH)2 = BasaKalsiumhidroksida • Ammonia = NH3 = bakalBasa NH4OH
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Indikator • Vinegar (cuka) = bersifat asam • Lemon juice (air jeruk) = bersifat asam • Air teh = cenderung basa • Sari jerukmengubah sifat basa air teh • Buktinya warna air tehdaricoklatmenjadi kuning
Senyawa spt dalam teh yang bisaberubah dari coklat menjadi kuning, ketika terjadi perubahan ke-asam/basa-an, bisa disebut sebagai indikator • Indikator menjadi penanda bahwa telah terjadi perubahan kimia dalam larutan • Indikator sintetis: phenolphtalein, methylene blue, bromokresol, dll.
Contoh asam yang populer • Cuka = larutan yang mengandung acetic acid = CH3COOH = HC2H3O2 = asam cuka
Sifat Asam • Dalam air melepaskan ion H+ • CH3COOH CH3COO- + H+ • Asam + Logam Garam + Hidrogen • CH3COOH + Mg (CH3COO)2Mg + H2 • Sifat mampu melepaskan Hidrogen ini yang mendasari sifat asam • Asam mengubah kertas litmus menjadi merah
Citric acid = Asam Sitrat • Air jeruk = larutan mengandung citric acid = H3C6H5O7= asam sitrat
Sifat Basa • Dalam air melepaskan ion OH- • NaOH Na+ + OH- • Basa + Asam Garam + Air • NaOH + CH3COOH CH3COONa + H2O
Teori awal Asam Basa • Tahun 1800-an awal: tiap molekul asam mengandung minimal satu atom H. • Th 1887 Svante Arrhenius (Bapak teori ionisasi): atom H berhubungan dengan sifat keasaman. Asam = donor H+ • HCl Cl- + H+ • CH3COOH CH3COO- + H+(dalam H2O) • CH3COOH CH3COO- + H3O+
Listrik Walau Terlarut CH3COOH maupun HCl Pelarut = Benzene = C6H6 Nonelectrolyte
Listrik Terlarut 0,5 M CH3COOH Asam Lemah Pelarut = Air Larutan ion dalam air = electrolyte
Listrik Terlarut 0,5 M HCl Asam Kuat Pelarut = Air Larutan ion dalam air = electrolyte
Asam sbg elektrolit • HCl Cl- + H+ • HCl dalam H2O (air) = strong electrolyte • CH3COOH CH3COO- + H+ • CH3COOH dalam H2O (air) = weak electrolyte • HCl dalam C6H6 (benzene) = non electrolyte
Basa sebagai elektrolit • NaOH Na+ + OH- • NaOH dalam H2O (air) = strong electrolyte • NH4OH NH4+ + OH- • NH4OH dalam H2O (air) = weak electrolyte • NH4OH dalam C6H6 (benzene) = non electrolyte
Konsep Asam dan Basa • Svante Arrhenius (1887): Asam = pemberi H+ Basa = penerima H+ • Gilbert N. Lewis (1916): Asam mendapatkan muatan – Basa mendapatkan muatan + • Johannes N. Bronsted & Thomas M. Lowry (1923): Asam = pemberi proton Basa = penerima proton
Arrhenius: HCl asam • Lewis: HCl juga asam • Bronsted & Lowry: HCl = juga asam • Yang berbeda alasannya • Saling melengkapi
Konstanta Ionisasi : Asam (Ka) dan Basa (Kb) • HCl H+ + Cl- [H+] [Cl-] Ka = 107 >102 [HCl] • Maka HCl digolongkan Strong Acid (asam kuat)
Ka Asam Lemah • CH3COOH CH3COO- + H+ [CH3COO-] [H+] Ka = = 1,8 x 10-5 [CH3COOH ] 10-8 < Ka CH3COOH < 10-3 • Maka CH3COOH digolongkanWeak Acid (asam lemah)
Strong Acid (Ka > 102) • Perchloric acid = HClO4 • Sulfuric acid = H2SO4 • Iodide acid = Hydrogen Iodide = HI • Bromide acid = Hydrogen Bromide = HBr • Chloride acid = Hydrogen Chloride = HCl • Nitric acid = HNO3
Weak Acid (10-8 < Ka < 10-3) • Acetic acid = CH3C00H • Carbonic acid = H2CO3 • Hydrogen Sulfide = H2S • Nitrous acid = HNO2 • H3PO4 , H2SO3
Ka Meningkat seiring Bil. Oksidasi Catatan: Ka HCl 107
Ka Air • H2O H+ + OH- [H+] [OH-] Ka = = 1 x 10-14 Pada [H2O]=1 mole/L, Didapatkan [H+] [OH-]= 1 x 10-14 mole/L Karena [H+] = [OH-] maka[H+] [OH-] = [H+] [H+] = [H+]2 Jadi[H+]2 = 1 x 10-14 dan[H+]= (1 x 10-14) = 1 x 10-7 dipermudah penulisannya: - log 1 x 10-7 = - log 10-7 = -(-7) = 7 Maka pH air murni = 7 [H2O]
Selanjutnya Ka (a=acid) Air menjadi Kw (w=water) [H+]2 = 10-14 [H+] [H+] [OH-] [H+] Kw Kw = = = 10-14 = 10-14 [H+] = 10-7 pH = -Log[H+] = -Log(10-7) pH air = 7 Kesetimbangan ion-ion dalam larutan didasarkan pada Kw air ini
Ka Air Kw • Air murni terurai sebagian H+ maupun OH- • Dalam suatu larutan ------dengan pelarut air, • ada juga ion H+ maupun OH- • Jika [H+] > [OH-], sifat asam, pH < 7 • Jika [H+] = [OH-], sifat netral, pH = 7 • Jika [H+] < [OH-], sifat basa, pH > 7 • Range pH • pH=1....................pH=7....................pH=14 • Asam...................Netral...................Basa
pH (Power of Hydrogen) • pH = - log [H+] • Problem: • Suatu larutan, volume 200 mL, diukur dg alat pH-meter ternyata pH-nya = 5 • Jika larutan diencerkan 10 x menjadi 2000 mL, berapa pH-nya sekarang?
pH (Power of Hydrogen) • pH = - log [H+] • 5 = - log [H+] • 5 = - (-5) • 5 = - (log 10-5) • Jadi [H+] = 10-5 mole/Liter
Diencerkan 10 x, • [H+] menjadi 10-5 x 10-1 mole/Liter • = 10-6 mole/Liter • pH sekarang = - (log 10-6) = -(-6) = 6 • Pengenceran membuat pH mendekati netral
pH Asam Kuat • Berapa pH dari larutan 0,01 M HCl? • HCl H+ + Cl- • Dalam air, Asam Kuat diasumsikan terdisosiasi sepenuhnya menjadi ion-ion, maka: • [H+] = [HCl] = 0,01 mole/L = 10-2 mole/L • pH = -Log(10-2) = -(-2) = 2
pH Basa Kuat • Berapa pH dari larutan 0,01 M NaOH? • NaOH Na+ + OH- • Dalam air, Basa Kuat diasumsikan terdisosiasi sepenuhnya menjadi ion-ion, maka: • [OH-] = [NaH] = 0,01 mole/L = 10-2 mole/L
Rumus kesetimbangan ion dalam air: • Kw = [H+] [OH-] = 10-14 • [H+] (10-2) = 10-14 • [H+] = 10-14/(10-2) = 10-12 • pH = -Log(10-12) = -(-12) = 12
The importance of pHPentingnya pH • The effectiveness of enzymes depends very much on pH • Efektivitas enzim- sangat tergantung pada pH tertentu • Plants grow best in soil in the right pH range (slightly basic or acidic) depending on the plant • Tanaman tumbuh baik pada kisaran pH tertentu (bisa basa maupun asam)
The rate of deterioration of metals, stone and concrete is determined largely by pH of the water to which they are exposed • Laju kerusakan logam, batu dan batu beton sangat ditentukan oleh air yang menerpa mereka • Rain water has been becoming more acidic because of increasing pollution of the atmosphere by SO2, NO2, etc. • Air hujan menjadi lebih asam karena polusi gas-gas SO2, NO2, dll.
pH Asam Lemah • Acetic acid CH3COOH memiliki Ka 1,75 x 10-5 • Jika konsentrasinya 0,1 M, berapa pHnya? • CH3COOH CH3COO- + H+ • (0,1-y) y y [CH3COO-] [H+] Ka = = 1,75 x 10-5 [CH3COOH]
(y2) = 1,75 x 10-5 (0,1 – y) Karena diasumsikan y sangat kecil, maka (0,1-y) dianggap = (0,1-0) = 0,1 sehingga (y) (y) Ka = = 1,75 x 10-5 (0,1 – y) y2 = 1,75 x 10-6
y = (1,75 x 10-6) 1/2 y = (1,751/2 x 10-6/2) -Log (y) = -Log(1,751/2 x 10-6/2) -Log (y) = -Log1,75) ½ + (-Log10-6/2) pH = -Log1,75½ + 3 pH = -Log1,322875656 + 3
pH = - Log1,322876 + 3 pH = - 0,121519024 + 3 pH = - 0,1 + 3 pH = 2,9
pH Basa Lemah • Ammonia NH4OH memiliki Kb 5,65 x 10-10 • Jika konsentrasinya 0,2 M, berapa pHnya? • NH4OH NH4+ + OH- • (0,2-y) y y [NH4+ ] [OH-] Kb = = 5,65 x 10-10 [NH4OH]
= 5,65 x 10-10 (y2) = 5,65 x 10-10 (0,2– y) Karena diasumsikan y sangat kecil, maka (0,2 - y) dianggap = (0,2 - 0) = 0,2 sehingga (y) (y) Kb = (0,2 – y) y2 = (5,65 x 10-10) 0,2
y2 = (1,13 x 10-10) y = (1,13 x 10-10)1/2 y = (1,13 1/2) x (10-5) y = 1.063014581 x 10-5 Karena NH4OH =Basa, maka y = [OH-] [OH-] = 1.063014581 x 10-5
[H+] [OH-] Kw = = 10-14 10-14 [H+] = [OH-] 10-14 [H+] = 1.063014581 x 10-5 [H+] = (1/1,063014581) x 10-14-(-5)
[H+] (0,940720869) x 10-9) =
pH = - Log(0,940720869) - Log(10-9) pH = - (-0,026539221) + 9 pH = +0,0 + 9 pH = 9,0
Self-Test: • Find the pH of solution in which [H+] = 6.38 x 10-6 mol/L. • Calculate [H+] for a solution of pH 8.37 • Calculate the pH of a strong base 1.0 x 10-3 M NaOH • Calculate the pH of a strong base 5.0 x 10-3 M Ba(OH)2 • Calculate the pH of a weak acid 2.0 x 10-3 M H2CO3 (Ka = 5.64 x 10-11)
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