Kimia. kesetimbangan asam dan basa
Transcript of Kimia. kesetimbangan asam dan basa
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KESETIMBANGAN ASAM & BASA
Oleh : Ahmad mulya
SMAN PINTAR KUANSING
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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
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• 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.
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Contoh asam yang populer
Cuka = larutan yang mengandung acetic acid = CH3COOH = HC2H3O2 = asam cuka
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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
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Citric acid = Asam Sitrat
• Air jeruk = larutan mengandung citric acid = H3C6H5O7= asam sitrat
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Sifat Basa
• Dalam air melepaskan ion OH-• NaOH Na+ + OH-
• Basa + Asam Garam + Air• NaOH + CH3COOH CH3COONa + H2O
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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+
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Listrik
Pelarut = Benzene = C6H6 Nonelectrolyte
Walau Terlarut CH3COOH maupun
HCl
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Listrik
Pelarut = Air Larutan ion dalam air = electrolyte
Terlarut 0,5 M CH3COOH Asam
Lemah
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Listrik
Pelarut = Air Larutan ion dalam air = electrolyte
Terlarut 0,5 M HClAsam Kuat
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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
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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
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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 protonBasa = penerima proton
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Arrhenius: HCl asamLewis: HCl juga asamBronsted & Lowry: HCl = juga asamYang berbeda alasannyaSaling melengkapi
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Konstanta Ionisasi : Asam (Ka) dan Basa (Kb)
HCl H+ + Cl-
Ka =[H+] [Cl-]
[HCl] 107
• Maka HCl digolongkan Strong Acid (asam kuat)
>102
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Ka Asam Lemah
CH3COOH CH3COO- + H+
Ka =[CH3COO- ] [H+ ]
[CH3COOH ]= 1,8 x 10-5
10-8 < Ka CH3COOH < 10-3
• Maka CH3COOH digolongkan Weak Acid (asam lemah)
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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
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Weak Acid (10-8 < Ka < 10-3)
Acetic acid = CH3C00HCarbonic acid = H2CO3
Hydrogen Sulfide = H2SNitrous acid = HNO2
H3PO4 , H2SO3
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Ka Meningkat seiring Bil. 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
Catatan: Ka HCl 107
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Ka AirH2O H+ + OH-
Ka =[H+] [OH- ]
[H2O]= 1 x 10-14
Pada [H2O]=1 mole/L,Didapatkan [H+] [OH- ]= 1 x 10-14 mole/LKarena [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) = 7Maka pH air murni = 7
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Kw = [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
Selanjutnya Ka (a=acid) Air menjadi Kw
(w=water)
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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
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pH (Potential of Hydrogen)
pH = - log [H+] Problem:Suatu larutan, volume 200 mL, diukur dg alat
pH-meter ternyata pH-nya = 5Jika larutan diencerkan 10 x menjadi 2000
mL, berapa pH-nya sekarang?
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• pH = - log [H+]
• 5 = - log [H+]
• 5 = - (-5)
• 5 = - (log 10-5)
• Jadi [H+] = 10-5 mole/Liter
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• 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
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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
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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
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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
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pH beberapa zatNama 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)
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The importance of 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)
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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.
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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
Ka =[CH3COO-] [H+ ]
[CH3COOH]= 1,75 x 10-5
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Ka =(y) (y)
(0,1 – y)= 1,75 x 10-5
(y2)
(0,1 – y)= 1,75 x 10-5
y2 = 1,75 x 10-6
Karena diasumsikan y sangat kecil, maka (0,1-y) dianggap = (0,1-0) = 0,1 sehingga
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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
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pH = - Log1,322876 + 3
pH = - 0,121519024 + 3
pH = - 0,1 + 3
pH = 2,9
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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
Kb =[NH4
+ ] [OH- ]
[NH4OH]= 5,65 x 10-10
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Kb =(y) (y)
(0,2 – y)= 5,65 x 10-10
(y2)
(0,2 – y)= 5,65 x 10-10
y2 = (5,65 x 10-10) 0,2
Karena diasumsikan y sangat kecil, maka (0,2 - y) dianggap = (0,2 - 0) = 0,2 sehingga
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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
[OH-] = 1.063014581 x 10-5
Karena NH4OH =Basa, maka y = [OH-]
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Kw = [H+] [OH- ] = 10-14
=[H+][OH- ]
10-14
=[H+]1.063014581 x 10-5
10-14
=[H+] (1/1,063014581) x 10-14-(-5)
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=[H+] (0,940720869) x 10-9)
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pH = - Log(0,940720869) - Log(10-9)
pH = - (-0,026539221) + 9
pH = +0,0 + 9
pH = 9,0
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Self-Test:
1.Find the pH of solution in which [H+] = 6.38 x 10-6 mol/L.
2.Calculate [H+] for a solution of pH 8.373.Calculate the pH of a strong base 1.0 x 10-3 M
NaOH 4.Calculate the pH of a strong base 5.0 x 10-3 M
Ba(OH)2 5.Calculate the pH of a weak acid 2.0 x 10-3 M
H2CO3 (Ka = 5.64 x 10-11)
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Semoga bermanfaatdaaaahhh....
ASSALAMU’ALAIKUM WR.WB