Kesetimbangan ion dalam Asam dan Basa

Senyawa paling banyak diproduksi Sulfuric acid = H2SO4 = Asam sulfat Hydrochloric acid = HCl = Asam Klorida Nitric acid = HNO3 = Asam Nitrat Sodium Hydroxide = NaOH = Basa Natrium hidroksida Calcium hydroxide = Ca(OH)2 = Basa Kalsium hidroksida Ammonia = NH3 = bakal Basa NH4OH

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Indikator Vinegar (cuka) = bersifat asam Lemon juice (air jeruk) = bersifat asam Air teh = cenderung basa Sari jeruk mengubah sifat basa air teh Buktinya warna air teh dari coklat menjadi kuning

Senyawa spt dalam teh yang bisa berubah 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+

Pelarut = Benzene = C6H6  Nonelectrolyte 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

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 [CH3COO- ] [H+ ] Ka = = 1,8 x 10-5 [CH3COOH ] CH3COOH  CH3COO- + H+ [CH3COO- ] [H+ ] Ka = = 1,8 x 10-5 [CH3COOH ] 10-8 < Ka CH3COOH < 10-3 Maka CH3COOH digolongkan Weak 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 Bilangan Oksidasi Acid Formula Oxidation Number Ka Hypochlorous HClO 1+ 5 x 10-8 Chlorous HClO2 3+ 1 x 10-2 Chloric HClO3 5+ 1 x 1010 Perchloric HClO4 7+ 1 x 1011 Ka= Konstanta ionisasi asam. Catatan: Ka HCl  107

Ka Air H2O  H+ + OH- Ka = [H+] [OH- ] [H2O] = 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

Selanjutnya Ka (a=acid) Air menjadi Kw (w=water) [H+] [OH- ] = 10-14 Kw = [H+] [H+ ] = 10-14 [H+ ]2 = 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) 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

pH beberapa zat Nama Zat pH Gastric juice (cairan lambung) 1 – 3 (Sangat asam) Lemons (bangsa Jeruk) 2,2 – 2,4 (Sangat asam) Vinegar (Cuka) 2,4 – 3,4 Wine (Anggur) 2,8 – 3,8 Apples 2,9 – 3,3 Oranges (bangsa Jeruk) 3-4 Beer 4-5 Urine (air kencing) 5-8 Water saturated with CO2 (bangsa minuman Sprite) 6 Cow’s milk (susu sapi) 6,3 – 6,6 Saliva (Air liur) 6,5 – 7,5 (netral) Blood (darah) 7,3 – 7,5 Household ammonia (NH4OH) 12 (Sangat basa)

The importance of pH Pentingnya 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 Ka = [CH3COO-] [H+ ] [CH3COOH] = 1,75 x 10-5 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 Ka = [CH3COO-] [H+ ] [CH3COOH] = 1,75 x 10-5

Ka = (y) (0,1 – y) = 1,75 x 10-5 (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 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]

Kb = (y) (0,2 – y) = 5,65 x 10-10 (y2) = 5,65 x 10-10 (0,2 – y) y2 Karena diasumsikan y sangat kecil, maka (0,2 - y) dianggap = (0,2 - 0) = 0,2 sehingga 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

Kw = [H+] [OH- ] = 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)