1 Salts, Acids, and Bases Chapter 11

2 Solutions Solutions are homogeneous mixtures Solute is the dissolved substance –Seems to “disappear” or “Takes on the state” of the solvent Solvent is the substance the solute dissolves in –Does not appear to change state –When both solute and solvent have the same state, the solvent is the component present in the highest percentage Solutions in which the solvent is water are called aqueous solutions –Water is often called the universal solvent

3 Solubility When one substance (solute) dissolves in another (solvent) it is said to be soluble –Salt is soluble in Water, –Bromine is soluble in methylene chloride When one substance does not dissolve in another they are said to be insoluble –Oil is insoluble in Water There is usually a limit to the solubility of one substance in another –Gases are always soluble in each other –Some liquids are always mutually soluble

4 Solutions & Solubility Molecules that are similar in structure tend to form solutions –Like dissolves like The solubility of the solute in the solvent depends on the temperature –Higher Temp = Larger solubility of solid in liquid –Lower Temp =Larger solubility of gas in liquid The solubility of gases depends on the pressure –Higher pressure = Larger solubility

5 The precipitation reaction that occurs when yellow potassium chormate, K 2 CrO 4 (aq), is mixed with a colorless barium nitrate solution, Ba(NO 3 ) 2 (aq)

6 The Solution Process - Ionic Compounds When ionic compounds dissolve in water they dissociate into ions –ions become surrounded by water molecules - hydrated When solute particles are surrounded by solvent molecules we say they are solvated

7 When solid sodium chloride dissolves, the ions are dispersed randomly throughout the solution

8 Polar water molecules interact with the positive and negative ions of a salt

9 Describing Solutions - Qualitatively A concentrated solution has a high proportion of solute to solution A dilute solution has a low proportion of solute to solution A saturated solution has the maximum amount of solute that will dissolve in the solvent –Depends on temp An unsaturated solution has less than the saturation limit A supersaturated solution has more than the saturation limit –Unstable

10 Solution Concentration Parts Per Million PPM = grams of solute per 1,000,000 g of solution PPM = mg of solute per liter of solution –1000 mg = 1 g Mass of Solution = Mass of Solute + Mass of Solvent

11 Chemical Packages - Moles We use a package for atoms and molecules called a mole A mole is the number of particles equal to the number of Carbon atoms in 12 g of C-12 One mole = x units The number of particles in 1 mole is called Avogadro’s Number 1 mole of C atoms weighs g and has 6.02 x atoms

12 One-mole samples of iron (nails), iodine crystals, liquid mercury, and powdered sulfur

13 Example #1 ¬Use the Periodic Table to determine the mass of 1 mole of Al 1 mole Al = g ­Use this as a conversion factor for grams-to-moles Compute the number of moles and number of atoms in 10.0 g of Al

14 ®Use Avogadro’s Number to determine the number of atoms in 1 mole 1 mole Al = 6.02 x atoms ¯Use this as a conversion factor for moles-to-atoms Example #1 Compute the number of moles and number of atoms in 10.0 g of Al

15 ¬Use Avogadro’s Number to determine the number of atoms in 1 mole 1 mole Al = 6.02 x atoms ­Use this as a conversion factor for atoms-to-moles Compute the number of moles and mass of 2.23 x atoms of Al Example #2

16 ®Use the Periodic Table to determine the mass of 1 mole of Al 1 mole Al = g ¯Use this as a conversion factor for moles-to-grams Compute the number of moles and mass of 2.23 x atoms of Al Example #2

17 Molar Mass The molar mass is the mass in grams of one mole of a compound The relative weights of molecules can be calculated from atomic masses water = H 2 O = 2(1.008 amu) amu = amu 1 mole of H 2 O will weigh g, therefore the molar mass of H 2 O is g 1 mole of H 2 O will contain g of oxygen and 2.02 g of hydrogen

18 Solution Concentration Molarity moles of solute per 1 liter of solution used because it describes how many molecules of solute in each liter of solution If a sugar solution concentration is 2.0 M, 1 liter of solution contains 2.0 moles of sugar, 2 liters = 4.0 moles sugar, 0.5 liters = 1.0 mole sugar, etc. molarity = moles of solute liters of solution

19 Properties of Acids Sour taste Change color of vegetable dyes React with “active” metals –Like Al, Zn, Fe, but not Cu, Ag or Au Zn + 2 HCl  ZnCl 2 + H 2 –Corrosive React with carbonates, producing CO 2 –Marble, baking soda, chalk CaCO HCl  CaCl 2 + CO 2 + H 2 O React with bases to form ionic salts –And often water

20 Properties of Bases Also Known As Alkalis Taste bitter Feel slippery Change color of vegetable dyes –Different color than acid –Litmus = blue React with acids to form ionic salts –And often water –Neutralization

21 Arrhenius Theory Acids ionize in water to H +1 ions and anions Bases ionize in water to OH -1 ions and cations Neutralization reaction involves H +1 combining with OH -1 to make water H + ions are protons OH - ions are called hydroxide ions Definition only good in water solution

22 Strength of Acids & Bases The stronger the acid, the more willing it is to donate H Strong acids donate practically all their H’s HCl + H 2 O  H 3 O +1 + Cl -1 Strong bases will react completely with water to form hydroxides CO H 2 O  HCO OH -1 Weak acids donate a small fraction of their H’s –The process is reversible, the conjugate acid and conjugate base can react to form the original acid and base HC 2 H 3 O 2 + H 2 O  H 3 O +1 + C 2 H 3 O 2 -1 Only small fraction of weak base molecules pull H off water HCO H 2 O  H 2 CO 3 + OH -1

23 Graphical representation of the behavior of acids in aqueous solution

24 Multiprotic Acids Monoprotic acids have 1 acid H, diprotic 2, etc. –In oxyacids only the H on the O is acidic In strong multiprotic acids, like H 2 SO 4, only the first H is strong; transferring the second H is usually weak H 2 SO 4 + H 2 O  H 3 O +1 + HSO 4 -1 HSO H 2 O  H 3 O +1 + SO 4 -2

25 Water as an Acid and a Base Amphoteric substances can act as either an acid or a base –Water as an acid, NH 3 + H 2 O  NH OH -1 –Water as a base, HCl + H 2 O  H 3 O +1 + Cl -1 Water can even react with itself H 2 O + H 2 O  H 3 O +1 + OH -1

26 Autoionization of Water Water is an extremely weak electrolyte –therefore there must be a few ions present H 2 O + H 2 O  H 3 O +1 + OH -1 all water solutions contain both H 3 O +1 and OH -1 –the concentration of H 3 O +1 and OH -1 are equal –[H 3 O +1 ] = [OH -1 ] = °C K w = [H 3 O +1 ] x [OH -1 ] = 1 x 10 25°C –K w is called the ion product constant for water –as [H 3 O +1 ] increases, [OH - ] decreases

27 Acidic and Basic Solutions acidic solutions have a larger [H +1 ] than [OH -1 ] basic solutions have a larger [OH -1 ] than [H +1 ] neutral solutions have [H +1 ]=[OH -1 ]= 1 x M [H +1 ] = 1 x [OH -1 ] [OH -1 ] = 1 x [H +1 ]

28 Example #2 ¬Determine the given information and the information you need to find Given [H +1 ] = 10.0 MFind [OH -1 ] ­Solve the Equation for the Unknown Amount Determine the [H +1 ] and [OH -1 ] in a 10.0 M H +1 solution

29 ®Convert all the information to Scientific Notation and Plug the given information into the equation. Given [H +1 ] = 10.0 M= 1.00 x 10 1 M K w = 1.0 x Example #2 Determine the [H +1 ] and [OH -1 ] in a 10.0 M H +1 solution

30 pH & pOH The acidity/basicity of a solution is often expressed as pH or pOH pH = -log[H 3 O +1 ]pOH = -log[OH -1 ] –pH water = -log[10 -7 ] = 7 = pOH water [H +1 ] = 10 -pH [OH -1 ] = 10 -pOH pH 7 is basic, pH = 7 is neutral The lower the pH, the more acidic the solution; The higher the pH, the more basic the solution 1 pH unit corresponds to a factor of 10 difference in acidity pOH = 14 - pH

31 The pH scale and pH values of some common substances

32 A pH meter

33 Indicator paper being used to measure the pH of a solution

34 Example #3 ¬Find the concentration of [H +1 ] Calculate the pH of a solution with a [OH -1 ] = 1.0 x M

35 ­Enter the [H +1 ] concentration into your calculator and press the log key log(1.0 x ) = -8.0 ®Change the sign to get the pH pH = -(-8.0) = 8.0 Example #3 Calculate the pH of a solution with a [OH -1 ] = 1.0 x M

36 ¬Enter the [H +1 ] or [OH -1 ]concentration into your calculator and press the log key log(1.0 x ) = -3.0 ­Change the sign to get the pH or pOH pOH = -(-3) = 3.0 ®Subtract the calculated pH or pOH from to get the other value pH = – 3.0 = 11.0 Calculate the pH and pOH of a solution with a [OH -1 ] = 1.0 x M Example #4

37 ¬If you want to calculate [OH -1 ] use pOH, if you want [H +1 ] use pH. It may be necessary to convert one to the other using 14 = [H +1 ] + [OH -1 ] pOH = – 7.41 = 6.59 ­Enter the pH or pOH concentration into your calculator ®Change the sign of the pH or pOH -pOH = -(6.59) ¯Press the button(s) on you calculator to take the inverse log or 10 x [OH -1 ] = = 2.6 x Example #5 Calculate the [OH -1 ] of a solution with a pH of 7.41

38 Calculating the pH of a Strong, Monoprotic Acid A strong acid will dissociate 100% HA  H +1 + A -1 Therefore the molarity of H +1 ions will be the same as the molarity of the acid Once the H +1 molarity is determined, the pH can be determined pH = -log[H +1 ]

39 Example #6 ¬Determine the [H +1 ] from the acid concentration HNO 3  H +1 + NO M HNO 3 = 0.10 M H +1 ­Enter the [H +1 ] concentration into your calculator and press the log key log(0.10) = ®Change the sign to get the pH pH = -(-1.00) = 1.00 Calculate the pH of a 0.10 M HNO 3 solution

40 Neutralization Reactions Acid-Base reactions are also called Neutralization Reactions Often we use neutralization reactions to determine the concentration of an unknown acid or base The procedure is called a titration. With this procedure we can add just enough acid solution to neutralize a known volume of a base solution –Or visa versa

41 Buffered Solutions Buffered Solutions resist change in pH when an acid or base is added to it. Used when need to maintain a certain pH in the system –Blood A buffer solution contains a weak acid and its conjugate base Buffers work by reacting with added H +1 or OH -1 ions so they do not accumulate and change the pH Buffers will only work as long as there is sufficient weak acid and conjugate base molecules present