Acids and Bases

Topic: Acids& Bases in a chemical reaction Unit: Acids and Bases Topic: Acids& Bases in a chemical reaction Objectives: To understand the definition of an acid and a base To learn how to identify acids and bases in a chemical reaction To learn how to identify the conjugate acid and conjugate base in a chemical reaction

Quickwrite Answer one of the questions below in 1-2 sentences: What do you know about acids??? What are some acids you have heard of??? What do you know about bases??? What are some bases you have heard of??

Acids and Bases Acids are very important substances All rain is that falls from sky comes to us slightly acidic They cause lemons to be sour In fact, acids were first recognized as substances that taste sour Vinegar tastes sour because acetic acid Lemons taste sour because of citric acid Bases or alkalis, are characterized by their bitter taste and slippery feel

The Arrhenius Model The first person to notice the nature of acids was Svante Arrhenius with his experiments with electrolytes Arrhenius postulated that acids produce hydrogen ions (H+) in aqueous solution and bases produce hydroxide ions (OH-) in solution H+ H+ H+ H+ H+ H+ OH- OH- OH- OH- OH- OH-

The Arrhenius Model For Example, when hydrogen chloride gas is dissolved in water, each molecule produces ions as follows: HCl(g)  H+(aq) + Cl-(aq) This solution is the strong acid known as hydrochloric acid On the other hand, when sodium hydroxide is dissolved in water NaOH(s)  Na+(aq) + OH-(aq) This solution called a strong base

What’s the difference between an Arrhenius acid and a base? Acids produce ______ions (H+) when dissolved in water and bases produce _____(OH-) ions when ______in water Ex: HCl(g)  H+(aq) + Cl-(aq) NaOH(s)  Na+(aq) + OH-(aq hydrogen Answer Bank Donor hydrogen Proton hydroxide Cl – Added hydronium Acceptor dissolved NH4+ hydroxide dissolved

The BrØnsted-Lowry Model The Arrhenius concept of acids and bases is limited because it only involves the hydroxide ion - only 1 kind of base - those that produce hydroxide ions A more general definition of acids and bases was suggested by the Danish chemist Thomas Lowry In the BrØnsted-Lowry model, an acid is a proton (H+) donor and a base is a proton acceptor The general reaction is: HA(aq) + H2O(l)  H3O+(aq) + A- Acid Base Conjugate Acid Conjugate Base

The BrØnsted-Lowry Model HA(aq) + H2O(l)  H3O+(aq) + A- According to the Bronsted-Lowry model, the general reaction that occurs when an acid is dissolved in water can best be represented as an acid (HA) donating a proton to the base (a water molecule) Notice, the water molecule accepts the proton and does not produce a +1 charge

The Bronsted-Lowry Model Cl- Cl- H H H H+ H+ H H H H H H H H HCl(aq) + H2O(l)  H3O+(aq) + Cl- Acid Donates proton Base Accepts proton

What is the difference between Bronstead-Lowry acid and base? A Bronstead-Lowry acid is a proton (H+) _____and a Bronstead-Lowry base is a proton______ HA(aq) + H2O(l)  H3O+(aq) + A- Water acts as a base even though it does not produce ______ ions (OH-) When water accepts a protons it forms the ________ion (H3O+) donor Answer Bank Donor hydrogen Proton hydroxide Cl – Added hydronium Acceptor dissolved NH4+ acceptor hydroxide hydronium

The Bronsted-Lowry Model An easy way to identify the acid and base in an acid-base reaction is to count the number of hydrogen atoms in each reactant and product Consider the reaction below: HCl + NH3  NH4+ + Cl- HCl has 1 hydrogen atoms and loses one to become Cl- NH3 has 3 hydrogen atoms gains one to become NH4+ 4 H atoms 4 H atoms 4 H atoms 4 H atoms 4 H atoms 4 H atoms 4 H atoms 1 H atoms 4 H atoms 3H atoms 3H atoms 3H atoms 3H atoms 3H atoms 3H atoms 3H atoms 3H atoms 3H atoms 4H atoms 0H atoms

The Bronsted-Lowry Model Recall, a Bronstead-Lowry acid is a proton (H+) donor and a Bronstead-Lowry base is a proton acceptor Using this definition you can see that HCl donates one H+ to NH3 so, HCl is the acid and NH3 is the base HCl + NH3  NH4+ + Cl- Donates a H+ Acid Accepts a H+ Base

Practice: Using your Brontead-Lowry definition of acid and bases, Identify the acid and base in following equations: 1) HCl + NH3  NH4+ + Cl – 2) HNO3 + H2O  H3O+ + NO3- acid base HCl NH3 acid base HNO3 H2O

Conjugate Acids & Bases The reaction below is reversible: HCl + NH3  NH4+ + Cl – But what happens when the reverse reactions takes place? The ions, NH4+ and Cl- act as the acid and base NH4+ becomes the conjugate acid by donating a proton Cl - becomes the conjugate base by accepting the proton

Conjugate Acids & Bases HCl + NH3  NH4+ + Cl – A conjugate acid is the molecule or ion formed when a proton is added to a base, in this case NH4+ A conjugate base is what remains of an acid molecule or ion after a proton is lost , in the is case Cl – Acid Base Conjugate Acid Conjugate Base

What is the difference between a conjugate acid and base? HCl + NH3  NH4+ + Cl – A conjugate acid is the molecule or ion formed when a _____ is added to a base, in this case____ conjugate base is what remains of an acid molecule or ion after a proton is _____, in the is case____ proton Answer Bank Donor hydrogen Proton hydroxide Cl – Added lost hydronium Acceptor dissolved NH4+ NH4+ lost Cl-

Conjugate Acids & Bases HCl + NH3  NH4+ + Cl – The acid HCl and conjugate base Cl – form what is called the conjugate acid-base pair The base NH3 and conjugate acid NH4+ form what is called the conjugate base-acid pair

Conjugate Acids and Bases conjugate acid-base pair HCl(aq) + NH3 (l)  NH4+ aq) + Cl- conjugate base-acid pair

Practice: Using the bronstead lowry definiton, identify the acid, base, conjugate acid and conjugate base in the reactions below NH3 + H2O ↔ NH4+ + OH- Acid Base Conjugate Acid Conjugate base NH4+ OH- H2O NH3

Summarize: An acid is any substance that donates a _______ A base is a proton______ Given the equation: HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq), H2O may be classified as a ______ because it accepts a proton In the above equation, HCl is an ____ because it is donating a proton Answer Bank Hydrogen(H+) base Hydroxide(OH–) Donates acceptor hydronium proton

Topic: Acid Concentration and pH Unit: Acids and Bases Topic: Acid Concentration and pH Objectives: To understand what determines the strength of an acid and base To understand ion product constant (K) for water To learn how to calculate the hydrogen and hydroxide concentration given the product constant for water To learn how to calculate pH or pOH given K

Quickwrite Answer one of the questions below in 1-2 sentences: Have you ever bitten into a lemon, what did it taste like??? Have you ever felt bleach?? What did it feel like????

Acid Strength Acid strength is determined by the amount or concentration of Hydrogen ions [H+] in solution Strong acids completely disassociate and ionize (dissolves) to produce H+ ions Versus, a weak acids only slightly disassociate and ionize (dissolve) to produce H+ ions

+ Weak Acids like HF only slightly disassociate ad ionize (dissolve) In other words, weak acids will produce less hydrogen ions when dissolved in water HF H F H+ H F H F F- F- F- H+ H+ H F F H F- HF F- H+ +

+ Strong acids Completely dissolve or disassociate and ionize in water In other words, strong acids will completely more hydrogen ions when dissolved in water HCl Cl- H+ Cl- Cl- Cl- H+ H+ H+ H+ Cl- Cl- Cl- H+ H+ HCl Cl- H+ +

What’s the difference between a weak acid and a strong acid? Acid strength is determined by the amount of ________ ions in solution Strong acids ________disassociate and ionize (dissolves) to produce H+ ions Versus, a weak acids only _____disassociate and ionize (dissolve) to produce H+ ions Hydrogen (H+) Answer Bank Hydrogen (H+) Greater than H2SO4 completely equal H2CO3 slightly Concentration Less than completely slightly

Strong and Weak Acids Strong acids Weak Acids HCl Hydrochloric Acid HC2H3O2 Acetic Acid H2SO4 Sulfuric Acid H3PO4 Phosphoric Acid HNO3 Nitric Acid H2CO3 Carbonic Acid

What are some strong and weak acids? Strong acids Weak Acids HCl Hydrochloric Acid HC2H3O2 Acetic Acid ________ Sulfuric Acid H3PO4 Phosphoric Acid HNO3 Nitric Acid _________ Carbonic Acid Answer Bank Hydrogen (H+) Greater than H2SO4 completely equal H2CO3 slightly Concentration Less than H2SO4 H2CO3

Water as an Acid and a Base A substance is said to be amphoteric if it can behave as an acid or as a base Water is the most common amphoteric substance The following reactions illustrates this point: H2O(l) ↔ H+(aq) + OH-(aq) Pure water only contains the hydrogen and hydroxide ions--in small amounts!

[OH-] = (1.0 x 10-7 M) [H+] = (1.0 x 10-7 M) Water as an Acid & a Base Pure water contains H+ ions in it This concentration is [H+] = 1.0 x 10-7 M Pure water contains OH- ions in it This concentration is [OH-] = 1.0 x 10-7 M It is important to realize that these concentration values are constant and equal [OH-] = (1.0 x 10-7 M) [H+] = (1.0 x 10-7 M) H+ OH- OH- H+ H+ OH- OH- H+ OH- H+ OH- H+

Water as an Acid & a Base = 1.0 x 10 -14 M We can find this constant by multiplying the concentrations of H+ & OH- Or, [H+] [OH-] = (1.0 x 10-7 M)(1.0 x 10-7 M) = 1.0 x 10 -14 M [H+] [OH-] = (1.0 x 10 -14 M) H+ OH- H+ OH- H+ H+ OH- OH- H+ OH- H+ OH-

Water as an Acid and a Base We call this constant Kw, or the ion product constant for water So now we can simply the expression into: [H+] [OH-] = (1.0 x 10 -14 M) = Kw The constant Kw is always equal to 1.0 x 10 -14 M

Water as an Acid and a Base This means that if the [H+] concentration goes up, then [OH-] concentration goes down, resulting in an acidic solution Or if we add more base [OH-], this will cause the hydrogen ion concentration [H+] to go down, resulting in a basic solution [H+] [OH-] = (1.0 x 10 -14 M) = Kw

What is the ion-product constant? Kw is the ion product constant for water It is the ___________of [H+] [OH-] ions in water It is equal to: Kw = (1.0 x 10 -14 M) = [H+] [OH-] Answer Bank Hydrogen (H+) Greater than H2SO4 completely equal H2CO3 slightly Concentration Less than concentration

the solution is neutral Water as an Acid & a Base If [H+] = [OH-] then the solution is neutral If [H+] > [OH-] then the solution is acidic If [H+] < [OH-] then the solution is basic If [H+] > [OH-] then the solution is acidic If [H+] < [OH-] then the solution is basic If [H+] = [OH-] then the solution is neutral H+ H+ H+ OH- OH- OH- H+ H+ OH- OH- OH- H+ H+ H+ H+ H+ H+ OH- OH- OH- OH- OH- OH- H+ H+ H+ H+ OH- OH- OH- OH- OH- OH- H+ H+ H+

What determines whether a solution will be acidic or basic? equal If [H+] is ______ to [OH-] then the solution is neutral If [H+] is ______ _____ [OH-] then the solution is acidic If [H+] is _____ _____ [OH-] then the solution is basic greater than Answer Bank Hydrogen (H+) Greater than H2SO4 completely equal H2CO3 slightly Concentration Less than less than

Practice: Solution: Because 1.0 x 10 -5 M > 1.0 x 10 -9 M A solution contains a hydrogen ion concentration of 1.0 x 10 -9 M ( [H+] = 1.0 x 10 -9 M ) and a hydroxide ion concentration of 1.0 x 10-5 M ( [OH-] = 1.0 x 10 -5 M ) Is the solution basic or acidic? Solution: Because 1.0 x 10 -5 M > 1.0 x 10 -9 M In other words, because [OH-] is greater than [H+], the solution is basic

Practice: 1.0 x 10 -5 M [OH-] solution: Calculate the [H+] ion concentration for a 1.0 x 10 -5 M [OH-] solution: Recall: Kw = (1.0 x 10 -14 M) = [H+] [OH-] We know that Kw = (1.0 x 10 -14 M) = [H+] [OH-] so we need to calculate and solve for [H+] [H+] = 1.0 x 10 -14 = 1.0 x 10 –9 M 1.0 x 10-5 We know that Kw = (1.0 x 10 -14 M) = [H+] [OH-] so we need to calculate and solve for [H+] 1.0 x 10 -14 M = [H+] [OH-] 1.0 x 10 -5 M

Practice: 10 M [H+] solution: Calculate the [OH-] ion concentration for a 10 M [H+] solution: Recall: Kw = (1.0 x 10 -14 M) = [H+] [OH-] 10 M [H+] Is the solution basic or acidic? We know that Kw = (1.0 x 10 -14 M) = [H+] [OH-] so we need to calculate [OH-] [OH-] = 1.0 x 10 -14 = 1.0 x 10 -14 = 1.0 x 10 –15 M [H+] 10 We know that Kw = (1.0 x 10 -14 M) = [H+] [OH-] so we need to calculate [H+] [H+] = 1.0 x 10 -14 = 1.0 x 10 -14 = 1.0 x 10 –9 M [OH-] 1.0 x 10-5

pH Scale Rather than use scientific notation, the pH scale was developed to simplify things pH is simple way to describe the very wide range of [H+] concentration pH is the negative logarithm of [H+] It is expressed as pH = -log [H+] pH values have no units However, to calculate pH, [H+] must be in molarity In other words, if you know [H+], you can find pH

pH Scale To calculate pH, you will need a calculator with a log button What is the pH of water? Remember, water has a molarity or [H+] concentration of 1.0 x 10-7 To calculate the pH of water, you would take the – log [H+] , or pH = – log (1.0 x 10-7) = 7 7 is a neutral pH Anything below 7 is acidic and anything above seven basic

pH

What’s the difference between acidic and basic? Acidic solutions have a pH _____ _____ 7 and basic solutions have a pH ____ ____ 7 (alkaline) Acids also have a ____ taste to them and bases have bitter taste smooth ______feel to them less than Answer Bank concentration Greater than(2) Basic sour pOH equal logarithm acidic Less than (2) slippery greater than sour slippery

Practice: Calculate the pH of a 0.0100 M HCl solution, [H+] = 0.0100 M pH = - log [H+] Remember, pH = - log [H+] So, pH = - log (0.0100) = 2

Practice: Calculate the pH of a 0.005 M HCl solution, [H+] = 0.005 M pH = - log [H+] Remember, pH = - log [H+] So, pH = - log [0.005] = ????

pOH We can also use the log scale to calculate pOH For example: pOH = - log [OH-] Therefore, a solution that has a molarity or hydroxide concentration of [OH-] = 1.0 x10 -12 M has a pOH of: -log [OH-] = -log(1.0 x10 -12 M ) = 12.00 Or pOH = 12

Remember, pOH = - log [OH-] Practice: Calculate the pOH for a solution that has hydroxide concentration of [OH-] of 1.0 x 10-3 M Remember, pOH = - log [OH-] So, pOH = - log (1.0 x 10-3 M) = 3.0

pH & pOH There is a convenient relationship between pH and pOH If you remember your Kw equation where Kw = [H+] [OH-] = 1.0 x 10-14 you can calculate pOH from pH By taking the negative log of both sides -log ( [H+] [OH-] ) = -log (1.0 x 10-14) We get –log [H+] –log [OH-] = -log (1.0 x 10-14) = 14 This gives us the equation pH + pOH = 14 So, this means that if you know either pH or pOH for a solution you can calculate the other

Practice: The pH of blood s about 7.4 (pH = 7.4) What is the pOH? pH + pOH = 14 We just learned that pH + pOH = 14 We know the pH of blood = 7.4 Plug this value into our equation we get: 7.4 + pOH = 14 pOH = 14 -7.4 = 6.6

Summarize: An acid is any substance that donates a _______ Acids have a ______ taste and produce______ ions in solution KOH is strong base because it easily releases _______ions HCl is a strong acid because it completely releases releasing _____ ions If [H+] is > [OH-] then the solution is_______ Answer Bank Hydrogen (H+) slippery sour Hydroxide (OH–) donates hydronium proton