Notes of Acid ,base and salt

Topic                  SLOs /  Content References 8.1Acids, Bases and Amphoteric Substances 8.1.1-Define acids, bases and amphoteric compounds; Theory Acid Base Arrhenius generates [H+] in solution generates [OH-] in solution Example NaOH                                     Na+ + OH- HCl                                    Cl- +   H+ Bronsted-Lowery anything that donates a [H+] (proton donor) anything that accepts a [H+] (proton acceptor Example HNO2          + H2O        →   NO2-        +        H3O+ (Porton donor)       (Proton acceptor )        Lewis accepts an electron pair donates an electron pair Example  Cl-      + FeCl3→[FeCl4]- (Base)      (Acid)  NH3 +   H+   →  NH4+ (Base)      (Acid) 8.1.2-explain the significance of acid base reactions in daily life 1- Food preservation             Acid such as vinegar ,lemon  lime juice  will preserved food because the pH is to high bacteria  to serviced 2- Allergic Reaction Acid solution prevent all allergic reaction HCl and NH4Cl used in cough syrups. Aunt biting  transfer  Formic acid (HCOOH) which inching  in the body 3- Gastric acidity when  a heart burn is experienced , actually concentration of HCl is sensation of burning When this people often Anta acid which contain base such as Al(OH)3 and Mg (OH)2 The stomach acid  react with  anat acid to produce  a salt and water  4-Curdling of milk:             Milk is comprised of several compounds, primarily fat, protein, and sugar. The protein in milk is normally suspended in a colloidal solution, which means that the small protein molecules float around freely and independently. These floating protein molecules refract light and give milk its white appearance.             Normally these protein molecules repel each other, allowing them to float about without clumping, but when the pH of their solution changes, they can suddenly attract one another and form clumps. This is exactly what happens when milk curdles. As the pH drops and becomes more acidic, the protein (casein) molecules attract one another and become "curdles" floating in a solution of translucent whey.             This clumping reaction happens more swiftly at warmer temperatures than it does at cold temperatures. 5-Improtantce of Iodine in salt             Human  body need iodine for thyroid to produce couple of essential hormones - thyroxie  and tri iodothgronie    The deficiency of iodine the decrease the intelligence (IQ) of person. it use full to remove toxic element such as bromine (Br) ,fluorine ( F)  and Lead(Pb) , Mercury(Hg)   8.1.3- Calculate  molarity, molality 8.2 Lowry - Bronsted Concept of Acids and Bases 8.2.1-Define acids and bases according to Lowry – Bronsted theory; In chemistry, the Brønsted-Lowry theory is an acid-base theory, proposed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923. In this system, Brønsted-Lowry acids and Brønsted-Lowry bases are defined as follows: an acid is a molecule or ion that is able to lose, or "donate," a hydrogen cation (H+, a proton); a base is a species with the ability to gain, or "accept," a hydrogen cation (a proton).  It follows that, if a compound is to behave as an acid by donating a proton, there must be a base to accept the proton. So the Brønsted-Lowry concept can be defined by the reaction: Acid + Base                    Conjugate base + Conjugate acid The conjugate base is the ion or molecule remaining after the acid has lost a proton, and the conjugate acid is the species created when the base accepts the proton. The reaction can proceed in either the forward or backward direction; in each case, the acid donates a proton to the base. Brønsted-Lowry acid-base theory has several advantages over Arrhenius theory. Consider the following reactions of acetic acid (CH3COOH), the organic acid that gives vinegar its characteristic taste: CH3COOH  + H2O ó  H3O+  + CH3COO- CH3COOH  + NH3 ó  NH4+  + CH3COO- Both theories easily describe the first reaction: CH3COOH acts as an Arrhenius acid because it acts as a source of H3O+ when dissolved in water, and it acts as a Brønsted acid by donating a proton to water. In the second example CH3COOH undergoes the same transformation, in this case donating a proton to ammonia (NH3), but this cannot be described using the Arrhenius definition of an acid because the reaction does not produce hydronium. https://www.boundless.com/chemistry/aqueous-reactions/acid-base-reactions/bronsted-acids-and-bases/ 8.3 Conjugate Acids and Bases 8.3.1-Define conjugate acid and conjugate base; Conjugate acid: A strong acid ionizes completely in an aqueous solution by losing one proton, according to the following equation:          HA (aq)                   H+ (aq) + A− (aq) where HA is a protonated acid, H+ is the free acidic proton, and A- is the conjugate base. Conjugate base of weak acid are strong for example             CH3COOH   ó  H+  + CH3COO- The CH3COO- ion is strong Conjugate base Conjugate base : A strong base  ionizes completely in an aqueous solution by accepting  one proton, according to the following equation:            BOH (aq)                   B+ (aq) + OH− (aq) where BOH is generate OH- is the free OH-, and   B+ is the conjugate acid . Conjugate acid of weak base are strong for example              NH4 OH ó  NH4+  + OH- The NH4+ ion is strong Conjugate acid   8.3.2 -Compare the strength of conjugate acids and bases; Strong acids yield weak conjugate bases. Strong acids completely dissociate into free protons and their conjugate base in water.            HCl   ó  H+  + Cl- The Cl- is weak conjugate  base   Conjugate base of weak acid are strong for example        CH3COOH   ó  H+  + CH3COO- The CH3COO- ion is strong Strong bases yield weak conjugate acid. Strong base completely dissociate into free OH- and their conjugate acid in water.            NaOH   ó  Na+  + OH- Conjugate acid of weak base are strong for example              NH4 OH ó  NH4+  + OH- The NH4+ ion is strong Conjugate acid  8.4 Strengths of Acids and Bases 8.4.1-Explain the ionization constant of water (Kw); H2O ó  H+  + OH- According to equilibrium constant l The concentration of water in water is 55.55 mol/dm3 The equilibrium constant is 1.x10 -16  Kw  =1x 10-14 =[ H+][OH-] Kw = [H+][OH-]   OR 1x 10-14 =[ H+][OH-] 1x 10-14 =[ H+][OH-] As we know that  when water dissociate it from equal H+ and OH- ions ,           [H+] = [OH-]  Suppose the concentration of H+  and  OH- ion is   X mol/dm3 1x 10-14 = X  .  X 1x 10-14 = X2  Taking square root on both side X= 1x 10-7 [H+]=1x 10-7 [OH-] = 1x 10-7 Therefore the pH and pOH is 7 According to dissociation of water Kw =1x 10-14 1x 10-14 =[ H+][OH-] Apply log on both side log 1x 10-14 = log [ H+] + log [OH-] Multiple by (-) on both side  -log 1x 10-14 ={ -log [ H+] }+{ -log [OH-]} As we know that pH = - log [ H+]                  ,   pOH = -log [OH-]   and  -log 1x10-14=14  pH +pOH =14 8.4.2-compare the strength of acids and bases using pH and pOH;             Acidic Strength increase                                                     Acidic Strength decrease   [H+] 100 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14 pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 [OH-] 10-14 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 10-14 pOH 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0                 Basic strength decrease                                                               Basic strength increase                                                                                                           Decrease  the concentration of OH-  will increase the pOH of solution,                Decrease  the concentration of H+  will increase the pH of solution, Increase  the concentration of OH-  will decrease the pOH of solution, Increase  the concentration of H+-  will increase the pH of solution                                     Acidic Strength increase   Ka 100 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14 pKa 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Kb 10-14 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 10-14 pKb 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0                                                                                                          Basic strength increase   To calculate a pH value, it is easiest to follow the standard "Start, Change, Equilibrium" process. Example Problem: Determine the pH of a 0.25 M solution of HBr. Answer:                               HBr                                H+          +         Br -   Initial                 0.25M                                Nil                    Nil    Equilibrium      (0.25M -0.25 M)                +0.25M         +0.25M  pH = -log [H+]       =   -log (0.25)       = 0.60   http://www.uiowa.edu/~chemrev/chem-basic/acid_base.htm 8.4.3- Derive the dissociation constants of acid, base and water  (Ka, Kb and  Kw); Dissociation of Acid CH3COOH  + H2O ó  H3O+  + CH3COO- Dissociation of Base NH3  + H2O ó  NH4+  +OH- Show That  Kw =Ka x Kb  CH3COOH  + H2O ó  H3O+  + CH3COO- CH3COO-   + H2O   ó CH3COOH + OH- Ka x Kb =     x Ka x Kb =     x Ka x Kb= [H3O+][OH-] According to dissociation constant of water Kw = [H3O+][OH-]   Since Kw = Ka x Kb 8.4.4- Calculate the H O3+ concentration by using the given Ka and molar concentration of weak acid; Example Problem: Determine the pH of .30 M acetic acid (              (CH3COOH) with the Ka of 1.8x10-5. Answer : Write the equilibrium equation for the acid CH3COOH  + H2O ó  H3O+  + CH3COO- Write the equilibrium expression and the Ka value : Ka =1.8x10-5                           CH3COOH  + H2O ó  H3O+  + CH3COO- At initial time      0.30M                       Nil           Nil At Equilibrium    0.30-x                          x            x Substitute the variable (disregard the “-x” because  it is so small compared to the 0.30 and solve for [H+] Ka =1.8x10-5 = x.x ÷  (0.30 –x)         1.8 x10-5= x2  ÷ (0.30 –x)                    x = 2.3x10-3 pH = - log [H+] http://www.uiowa.edu/~chemrev/chem-basic/acid_base.htm                                                                                  8.4.5- Explain the term ‘leveling effect’; 8.5 Lewis Concept of Acids and Bases 8.5.1-Define Lewis acids and bases along with examples; In 1923 G. N. Lewis suggested another way of looking at the reaction between H+ and OH- ions. In the Bronsted model, the OH- ion is the active species in this reaction  it accepts an H+ ion to form a covalent bond. In the Lewis model, the H+ ion is the active speciesit accepts a pair of electrons from the OH- ion to form a covalent bond. In the Lewis theory of acid-base reactions, bases donate pairs of electrons and acids accept pairs of electrons. A Lewis acid is therefore any substance, such as the H+ ion, that can accept a pair of nonbonding electrons.  In other words, a Lewis acid is an electron-pair acceptor. A Lewis baseis any substance, such as the OH- ion, that can donate a pair of nonbonding electrons.  A Lewis base is therefore an electron-pair donor. The Lewis theory suggests that acids react with bases to share a pair of electrons, with no change in the oxidation numbers of any atoms. Many chemical reactions can be sorted into one or the other of these classes. Either electrons are transferred from one atom to another, or the atoms come together to share a pair of electrons. http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch11/lewis.php 8.5.2-Classify the given compounds (e.g. NH3, AlCl3, BF3, etc.) as Lewis acids or bases;