CHEMISTRY Chapter 14 ACID-BASE CHEMISTRY 2 ACID-BASE • Definition of Acids and Bases • Acid Strength: Weak or Strong • pH scale • Calculating pH • Base strength • Acid-base of salts • Buffers •...

this is an exams a general chemistry exams chm 112 and its timed 1 hour 30 min I will be taking pictures of the exmas and send it whiles the expert work on it and send me the answers and show of work its only 20 questions the expert gotta be fast and accurate because once the time ran out the exams closes the exams is due july 23 2021 at 12:30



CHEMISTRY Chapter 14 ACID-BASE CHEMISTRY 2 ACID-BASE • Definition of Acids and Bases • Acid Strength: Weak or Strong • pH scale • Calculating pH • Base strength • Acid-base of salts • Buffers • Titrations BASIC DEFINITIONS • We will use several definitions of acids and bases • The simplest is an acid is a substance that has a H+ to donate • A base has a OH- to donate • We will expand on those definitions as we go on 3 4 COMMON ACIDS 5 COMMON BASES 6 STRUCTURE OF ACIDS oxy acids have acid hydrogens attached to an oxygen atom H2SO4, HNO3 7 STRUCTURE OF BASES most ionic bases contain OH ions • NaOH, Ca(OH)2 some contain CO3 2- ions • CaCO3 NaHCO3 molecular bases contain structures that react with H+ • mostly amine groups 8 INDICATORS chemicals which change color depending on the acidity/basicity many vegetable dyes are indicators anthocyanins litmus • from Spanish moss • red in acid, blue in base phenolphthalein • found in laxatives • red in base, colorless in acid This chart illustrates the ranges of color change for several acid-base indicators. 9 10 THEORY: ARRHENIUS bases dissociate in water to produce OH- ions and cations • ionic substances dissociate in water NaOH(aq) → Na+(aq) + OH–(aq) acids ionize in water to produce H+ ions and anions •because molecular acids are not made of ions, they cannot dissociate • they must be pulled apart, or ionized, by the water HCl(aq) → H+(aq) + Cl–(aq) • in formula, ionizable H written in front HC2H3O2(aq) → H +(aq) + C2H3O2 –(aq) 11 HYDRONIUM ION the H+ ions produced by the acid are so reactive they cannot exist in water H+ ions are protons instead, they react with a water molecule(s) to produce complex ions, mainly hydronium ion, H3O + H+ + H2O → H3O + 12 PROBLEMS WITH ARRHENIUS THEORY • does not explain why molecular substances, like NH3, dissolve in water to form basic solutions – even though they do not contain OH– ions • does not explain how some ionic compounds, like Na2CO3 or Na2O, dissolve in water to form basic solutions – even though they do not contain OH– ions • does not explain why molecular substances, like CO2, dissolve in water to form acidic solutions – even though they do not contain H+ ions • does not explain acid-base reactions that take place outside aqueous solution 13 THEORY: BRØNSTED-LOWRY in a Brønsted-Lowry Acid-Base reaction, an H+ is transferred • does not have to take place in aqueous solution • broader definition than Arrhenius acid is H+ donor, base is H+ acceptor • base structure must contain an atom with an unshared pair (lone pair) of electrons in an acid-base reaction, the acid molecule gives an H+ to the base molecule 14 BRØNSTED-LOWRY ACIDS Brønsted-Lowry acids are H+ donors • any material that has H can potentially be a Brønsted-Lowry acid • because of the molecular structure, often one H in the molecule is easier to transfer than others HCl(aq) is acidic because HCl transfers an H+ to H2O, forming H3O + ions • water acts as base, accepting H+ HCl(aq) + H2O(l) → Cl –(aq) + H3O +(aq) acid base 15 BRØNSTED-LOWRY BASES Brønsted-Lowry bases are H+ acceptors • any material that has atoms with lone pairs can potentially be a Brønsted-Lowry base • because of the molecular structure, often one atom in the molecule is more willing to accept H+ transfer than others NH3(aq) is basic because NH3 accepts an H + from H2O, forming OH –(aq) • water acts as acid, donating H+ Memorize these! 16STRONG ACIDS AND BASES 17 AMPHOPROTIC SUBSTANCES amphoprotic substances can act as either an acid or a base • have both transferable H and atom with lone pair water acts as base, accepting H+ from HCl HCl(aq) + H2O(l) → Cl –(aq) + H3O +(aq) water acts as acid, donating H+ to NH3 NH3(aq) + H2O(l) ⇔ NH4 +(aq) + OH–(aq) 18 CONJUGATE PAIRS In a Brønsted-Lowry Acid-Base reaction, the original base becomes an acid in the reverse reaction, and the original acid becomes a base in the reverse process each reactant and the product it becomes is called a conjugate pair the original base becomes the conjugate acid; and the original acid becomes the conjugate base CONJUGATE ACID BASE PAIRS Water is the acid, OH- is its conjugate base Ammonia is the base, NH4 + is its conjugate acid 19 20 IDENTIFY THE BRØNSTED-LOWRY ACIDS AND BASES AND THEIR CONJUGATES IN THE REACTION H2SO4 + H2O ⇔ HSO4 – + H3O + acid base conjugate conjugate base acid H2SO4 + H2O ⇔ HSO4 – + H3O + When the H2SO4 becomes HSO4 −, it lost an H+ − so H2SO4 must be the acid and HSO4 − its conjugate base When the H2O becomes H3O +, it accepted an H+ − so H2O must be the base and H3O + its conjugate acid FIGURE 14.7 This diagram shows the relative strengths of conjugate acid-base pairs, as indicated by their ionization constants in aqueous solution. 21 22 POLYPROTIC ACIDS often acid molecules have more than one ionizable H – these are called polyprotic acids • the ionizable H’s may have different acid strengths or be equal • 1 H = monoprotic, 2 H = diprotic, 3 H = triprotic • HCl = monoprotic, H2SO4 = diprotic, H3PO4 = triprotic polyprotic acids ionize in steps • each ionizable H removed sequentially removing of the first H automatically makes removal of the second H harder • H2SO4 is a stronger acid than HSO4 − 23 ACID IONIZATION CONSTANT, KA acid strength measured by the size of the equilibrium constant when react with H2O HAcid + H2O ⇔ Acid -1 + H3O +1 the equilibrium constant is called the acid ionization constant, Ka • larger Ka = stronger acid 24 AUTOIONIZATION OF WATER Water is actually an extremely weak electrolyte • therefore there must be a few ions present about 1 out of every 10 million water molecules form ions through a process called autoionization H2O ⇔ H + + OH– H2O + H2O ⇔ H3O + + OH– all aqueous solutions contain both H3O + and OH– • the concentration of H3O + and OH– are equal in water • [H3O +] = [OH–] = 10-7M @ 25°C 25 ION PRODUCT OF WATER the product of the H3O + and OH– concentrations is always the same number the number is called the ion product of water and has the symbol Kw [H3O +] x [OH–] = Kw = 1 x 10 -14 @ 25°C • if you measure one of the concentrations, you can calculate the other as [H3O +] increases the [OH–] must decrease so the product stays constant • inversely proportional 26 ACIDIC AND BASIC SOLUTIONS all aqueous solutions contain both H3O + and OH– ions neutral solutions have equal [H3O +] and [OH–] • [H3O +] = [OH–] = 1 x 10-7 acidic solutions have a larger [H3O +] than [OH–] • [H3O +] > 1 x 10-7; [OH–] < 1="" x="" 10-7="" basic="" solutions="" have="" a="" larger="" [oh–]="" than="" [h3o="" +]="" •="" [h3o="" +]="">< 1="" x="" 10-7;="" [oh–]=""> 1 x 10-7 27 PH the acidity/basicity of a solution is often expressed as pH pH = -log[H3O +] [H3O +] = 10-pH • exponent on 10 with a positive sign • pHwater = -log[10 -7] = 7 • need to know the [H+] concentration to find pH pH < 7="" is="" acidic;="" ph=""> 7 is basic, pH = 7 is neutral 28 pH=1 pH=14pH=7 Strong acid Neutral Strong Base Weak acid Weak base FIGURE 14.5 (a) A universal indicator assumes a different color in solutions of different pH values. Thus, it can be added to a solution to determine the pH of the solution. The eight vials each contain a universal indicator and 0.1-M solutions of progressively weaker acids: HCl (pH = l), CH3CO2H (pH = 3), and NH4Cl (pH = 5), deionized water, a neutral substance (pH = 7); and 0.1-M solutions of the progressively stronger bases: KCl (pH = 7), aniline, C6H5NH2 (pH = 9), NH3 (pH = 11), and NaOH (pH = 13). (b) pH paper contains a mixture of indicators that give different colors in solutions of differing pH values. (credit: modification of work by Sahar Atwa) 29 30 https://www.google.com/imgres?imgurl=http://images.slideplayer.com/37/10684531/slides/slide_7.jpg&imgrefurl=http://slideplayer.com/slide/10684531/&docid=DygT9b76iO0ryM&tbnid=--v-EAqiP7ox4M:&vet=1&w=960&h=720&hl=en&bih=581&biw=1231&q=14%20on%20the%20ph%20scale&ved=0ahUKEwirhYmavJjSAhVJ6YMKHSU7DpAQMwgcKAAwAA&iact=mrc&uact=8 FIGURE 14.4-HOW WE MEASURE PH (a) A research-grade pH meter used in a laboratory can have a resolution of 0.001 pH units, an accuracy of ± 0.002 pH units, and may cost in excess of $1000. (b) A portable pH meter has lower resolution (0.01 pH units), lower accuracy (± 0.2 pH units), and a far lower price tag. (credit b: modification of work by Jacopo Werther) 31 FIGURE 14.3-ACID RAIN (a) Acid rain makes trees more susceptible to drought and insect infestation, and depletes nutrients in the soil. (b) It also is corrodes statues that are carved from marble or limestone. (credit a: modification of work by Chris M Morris; credit b: modification of work by “Eden, Janine and Jim”/Flickr) 32 PRACTICE What is the pH of a solution with a hydronium concentration of 2.4 X 10 -6? pH = -log[H3O +] pH = -log(2.4 X 10 -6) pH=5.62 33 34 POH another way of expressing the acidity/basicity of a solution is pOH pOH = -log[OH−], [OH−] = 10-pOH • pOHwater = -log[10 -7] = 7 • need to know the [OH−] concentration to find pOH pOH < 7="" is="" basic;="" poh=""> 7 is acidic, pOH = 7 is neutral 35 RELATIONSHIP BETWEEN PH AND POH the sum of the pH and pOH of a solution = 14.00 • at 25°C • can use pOH to find pH of a solution POH pH+ pOH = 14.0 With bases easier to calculate pOH and then find pH. Always measure pH 36 FIGURE 14.2 The pH and pOH scales represent concentrations of [H3O +] and OH−, respectively. The pH and pOH values of some common substances at standard temperature (25 °C) are shown in this chart. 37 38 PK a way of expressing the strength of an acid or base is pK pKa = -log(Ka), Ka = 10 -pKa pKb = -log(Kb), Kb = 10 -pKb the stronger the acid, the smaller the pKa • larger Ka = smaller pKa • because it is the –log 39 FINDING THE PH OF A STRONG ACID there are two sources of H3O + in an aqueous solution of a strong acid – the acid and the water for the strong acid, the contribution of the water to the total [H3O +] is negligible • shifts the Kw equilibrium to the left so far that [H3O +]water is too small to be significant •
Jul 22, 2021
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