Acid and Base Concepts
September 11, 2022 | Author: Anonymous | Category: N/A
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Acid and Base Concepts
1. Theory of Acid and Bases according to Arrhenius The acid acid soluti solution on and the basic basic soluti solution on are electro electrolyt lytee compou compounds nds.. Acid Acid base base compounds are commonly found in everyday life, such as orange juice, mango, pineapple, vinegar, soap, ammonia. Svante Arrhenius proposes the following basic acidic concepts c oncepts Acid is a compound if dissolved into water will give hydrogen ions ( !" in a solution, a base is a compound which, when dissolved into water, will give hydro#ide ions ($ %" in a solution. &n this case, the nature of the acid is the ! ion and the carrier of the basic property is the $% ion. The ionisation reaction occurring in Arrhenius acids and bases is generally written as follows. x− ¿
Z (aq ) ( acid ) +¿
H ( aq )+ ¿ H X Z ( aq) → x ¿ −¿
xOH ( xaq+)¿( base ) M ( aq) + ¿ M ( OH ) x ( aq) → ¿ '. Bronsted%owry Acid Base Theory &n 1)'*, +ohannes . Bronsted and Thomas . owry proposed the concept of acid base based on proton removal (!". According to Bronsted%owryAcid Species that can provide proton or proton donor ( !". Bases species that can accept proton or proton acceptor (!".
−¿ ¿ + ¿ +OH ¿ N H 3+ H 2 O ⇌ N H 4 * acts as a base, after receiving the proton transforms into / ! ions which act as acids by passing protons to $ %. '" acts as an acid, after handing the proton of * turns into $%. The $ ion acts as a base after receiving the proton from the /! ion. The acid% base pair after the proton handover is called the conjugate acid base. An acid after releasing a proton will form a species called a conjugate base of the base. The sessions are a base because they can absorb proton and re%form the original acid.
+ust as with acid, bases can also form a species called conjugate acids of the base. &t is an acid because it can remove one proton and reshape the base. &n a chemical reaction, the Bronsted%owry acid base can form two pairs of conjugate base acids. 0ouples consisting of acids with a conjugate base are characteried by acids 1 and base 1. 0ouples consisting of bases with conjugate acid differ differ only one proton (!". 2#ample-
−¿
H ( aq)
−¿ + H 2 O(l ) ⇌ H 2 CO 3( aq) + O ¿ ¿
HCO3 (aq ) Base
1
Acid ' Acid 1
Base '
%
%
So as to obtain the constituent acid base pair 0$ * and '0$* and '$ and $ . 3ith % '0$* as conjugate acid and $ as the conjugate base. Several provisions of acid%base as follows a. The acid%base acid%base properties properties of the substance substance are are determined determined by by the solven solvent. t. b. The easier it is to release protons, the stronger the acidity, the easier it will be to bind protons, the more powerful they become. The Bronsted% Bronsted%owry owry acid%base concept concept is broader broader than Arrhenius4s Arrhenius4s acid%base concept. concept. This is due to the following. a. The acid%b acid%base ase concep conceptt of Bronst Bronsted% ed%ow owry ry is not limited limited in water solvent solvents, s, but also describes acid%base reactions in other solvents or even solventless reactions. b. Bronsted%owry acid and base are not only molecules but also cations and anions. The acid%base concept of Bronsted%o Bronsted%owry wry can e#plain, e#plain, for e#ample, e#ample, the /0l acid ! properties. &n /0l, the acidic is the / ion, because the /0l in water releases the proton. Based on the concept of acid%base Bronsted%owry water can be as acid (proton donor" and as a base (proton acceptor". Such substances have amphiphic (amphoteric" properties, meaning they can act as bases and act as acids. *. ewis Acid Base Theory
−¿ ¿ +¿ + Cl ¿ N H 3+ HCl ⇌ N H 4
&n the above reaction, ! ions released by 0l can be bound by * molecules. Based on the Bronsted%owry acid%base theory, this proton binding ability is nothing else because it has a free electron pair used to form covalent covalent coordination coordination bonds, meaning meaning the free electron ! pair on * is used together with the ion. The coordinated covalent bond by 5ilbert . ewis is described as follows.
+¿
+ ¿ → N H 4 ¿ ¿ H 3 N :: + H
Based on the transfer of the electron pair, ewis defines the acid base as follows. Acid- a species acting as a receiver of electron pairs (electron acceptor" Bases- a species that acts as an electron%pairing (electron donor" &n the e6uation, the * molecule is a base, because * can give the pair of electrons, while the ! ion is an acid because it can accept the pairs of electrons. The advantage of ewis4s theory is that it can recognie substances as an acid that does not contain hydrogen, but has acidic properties such as ordinary hydrogen. 2#ample-
−¿
−¿ → HSO 4¿ ¿ SO3+ OH acid
base
ewis4ss acid%ba ewis4 acid%base se concep conceptt can e#plain e#plain acid%b acid%base ase reactio reactions, ns, althoug although h they they do not ! involve protons ( ions". Thus all Arrhenius acidic acids and Bronsted%owry acid bases meet ewis4s acid%base definition.
Derajat keasaman (pH)
p atau derajat 7easaman diguna7an untu7 menyata7an ting7at 7easaman (7ebasaan yang dimili7i oleh larutan". 8easaman yang dima7sud adalah 7onsentrasi ion hydrogen ( !" dalam pelarut air. ilai p ber7isar 9 hingga 1/. Suatu larutan di7ata7an netral apabila
memili7i nilai p :. ilai p ; : menunju77an larutan memili7i sifat basa, sedang7an pal7alis". ilai p 7urang dari : menunju7an ling7ungan masam sedang sed ang7an 7an nilai nilai p diatas diatas : menunj menunju77 u77an an ling7u ling7unga ngan n basa basa (al7alin (al7alin". ". Sedang Sedang7an 7an p: p: disebut sebagai netral. ?lu7tuasi p air sangat ditentu7an oleh al7alinitas air tesebut. Apabila al7alinitasnya tinggi ma7a air tersebut a7an mudah mengembali7an pnya 7enilai semula, dari setiap @gangguan terhadap pengubahan p. engan demi7ian 7unci dari penurunan p terleta7 pada penanganan al7alinitas dan ting7at 7esadahan air. Apabila hal ini telah di7uasai ma7a penurunan p a7an lebih mudah dila7u7an. dila 7u7an. egree of acidity (p" The p or degree of acidity is used to e#press the level of acidity (the basicity possessed by the solution". s olution". The acidity in 6uestion is the concentration of hydrogen ions ( !" in the water solvent. The p value ranges from 9 to 1/. A solution is said to be neutral if it has a p value of :. The p value; : indicates the solution has an al7aline property, whereas p base solution. The resulting color is strongly influenced by the p levels in the solution. ot all creatures can withstand p value changes, for it has provided a uni6ue mechanism for change not to occur but in a slow way. This defense system is 7nown as the
buffer4s capacity. capacity. p is very important as a water 6uality parameter because it controls the type and rate of reaction rates of some materials in water. Besides fish and other a6uatic creatures live on a certain p interval, so that by 7nowing the value of p then we will 7now whether wheth er the water is suitable suitable or not to support their lives. The p ranges range from 9 (very acidic" to 1/ (very al7aline > al7aline". A p value of less than : indicates a sour environment whereas a p value above : indicates an al7aline environment. 3hile p : is referred to as neutral. ?luctuations in water p are strongly determined by the al7alinity of the water. 3 3hen hen al7al al7alin init ity y is high high th then en th thee water water wi will ll ea easil sily y re resto store re its or orig igin inal al p va valu lue, e, from from an any y CdisturbanceC to p alteration. Thus the 7ey to the decrease in p lies in the handling of al7alinity and water hardness. &f this has been mastered then the decrease in p will be easier to do. Larutan penyangga.
arutan aru tan pe peny nyan angg ggaa ad adal alah ah laru laruta tan n ya yang ng da dapa patt memp memper erta tahan han7a 7an n p. p. aru arutan tan penyangga disebut juga buffer atau dapar. Disalnya di dalam air murni (p:" ditambah7an sedi7it basa, ma7a p a7an nai7. Bila 7ita masu77an 9,91 D a$ 7e dalam air, ma7a p a7an menjadi 1'. emi7ian juga sebali7nya bila 7ita masu77an sedi7it asam 7e dalam air. p a7an turun. +adi air murni tida7 memili7i 7emampuan mempertahan7an p. Des7ipun 7edalam larutan penyangga ditambah7an sedi7it asam atau sedi7it basa atau dila7u7an proses pengenceran, pengenceran, ma7a p tida7 berubah. berubah. Sebali7nya, Sebali7nya, penambahan penambahan asam atau basa dalam larutan bu7an penyangga menyebab7an perubahan p larutan yang drastis. 0ontoh- ion asetat segera menang7ap ! dari asam dan ion $ % dari basa berea7si dengan asam asetat. Buffer solution. The buffer solution is a solution which can maintain p. The buffer solution is also called buffer or buffer. ?or e#ample in pure water (p :" is added slightly base, then p will rise. &f we enter 9.91 D a$ into water, then the p will be 1'. Similarly vice versa if we put a little acid into the water. p will go down. So pure water does not have the ability to maintain p. Although the buffer solution is added slightly or slightly al7aline or diluted, the p is unchanged. 0onversely, addition of an acid or base in a non%buffering solution causes a drastic change in p of the solution. 2#ample- Acetate 2#ampleAcetate ions immediately immediately catch ! from acid and $% ions from the base react with acetic acid.
+ ¿ →CH 3 COOH −¿ + H ¿ ¿
C H 3 COO
−¿ + H 2 O
−¿ → CH 3 COO¿ ¿ CH 3 COOH + OH +i7a larutan penyangga ditambah asam atau basa yang sangat besar (larutan penyangga habis berea7si", ma7a p larutan penyangga berubah drastic. p larutan penyangga dihitung berdasar7an berdasar7an sifat larutan penyangga. 1. arut rutan penyangga 7onjungasinya".
asa sam m
(larutan tan
peyan ang gga
dari
as asaam
lema emah
dan
basa
&f the buffer solution is added with a very large acid or base (the buffer solution runs out", the p of the buffer solution changes changes drastically. The p of the buffer solution is calculated based on the nature of the buffer solution. 1. Acid buffer solution (peyangga solution of wea7 acid and its conjunctive base".
+¿ ¿ −¿ + H CH 3 COOH
⇌
¿
C H 3 COO
H
¿ +¿
CH
−¿
¿
C H 3 COO
¿ ¿
[ ¿ ¿ 3 COOH ] ¿ ¿ ¿ a a pH =− K a . atau pH = p K a− log =−log K
( )
g '. arut rutan penyangga 7onjungasinya".
g basa (l (laarutan penyan ang gga
dar arii
basa lemah dan
Basic buffer solution (buffer solution of wea7 base and conjunctive acid".
−¿ ¿ + ¿ + OH ¿ N H 3+ H 2 O ⇌ NH 4
asam
O H
¿ −¿ NH
+¿ NH 4
¿
¿ ¿ [ ¿¿ 3] ¿ ¿ ¿
( )
p pO O H =− log K K b .
b b atau ata u p O H = p K b− log g g
8eterangana jumlah mol asam lemah b jumlah mol basa lemah g jumlah mol asam 7onjugasi>basa 7onjugasi &nformationa number of moles of wea7 acids b low mol amount of base g number of moles of conjugate acid > conjugate base
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