Principles of Chem II
Principles of Chem II CHEM 1212
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This 3 page Class Notes was uploaded by Vesta Rippin on Monday October 12, 2015. The Class Notes belongs to CHEM 1212 at Georgia College & State University taught by Staff in Fall. Since its upload, it has received 17 views. For similar materials see /class/221958/chem-1212-georgia-college-state-university in Chemistry at Georgia College & State University.
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Date Created: 10/12/15
ICHEM 1212 Principles of Chemistry 11 Chapter 15 Applications of Aqueous Equilibria 151 Solutions of Acids or Bases Containing a Common Ion I in this section we discuss solutions that contain not only the weak acid HA but also its salt NaA I consider a solution containing the weak acid HF Ka 72 H 104 and its salt sodium uoride NaF I the reactions are HFaq ltgt Haq Fraq and NaFs gt Naaq F39aq I the common ion is the uoride ion when uoride is added to a solution containing HF the equilibrium is shifted to the left I this is known as the common ion effect 152 Buffered Solutions I the most important application of acidbase solution containing a common ion is for buffering I a buffered solution is on that resists a change in its pH when either hydroxide ions or protons are added I blood is buffered I a buffered solution may contain a weak acid and its salt or a weak base and its salt I by choosing the appropriate components a solution can be buffered at Virtually any pH Buffering How Does It Work HAaQ ltgt HaQ ATM I rst case what happens when a strong base is added HAaQ 0H39aQ gt H20aQ A39aQ I since A39aq is already present in the original solution in a much high amount than that of the base added the change in the HAA39 will be small RFGCSU Ch 15 Zumdahl 7th Eddoc Page 1 of 3 I second case what happens when a strong acid is added A39aQ t HaQ gt HAWI I since HAaq is already present in the original solution in a much high amount than that of the base added the change in the HAA39 will be small thus the H and the pH remain essentially constant I an important equation when dealing with buffers is the HendersonHasselbach equation pH pKa log A39HA or pH pKa log baseacid 153 Buffer Capacity I the buffering capacity of a buffered solution represents the amounts of protons or hydroxide ions the buffer can absorb without a signi cant change in pH I the capacity of a buffer is determined by the HA and A39 I the ratio A39 HA should be close to l for most efficient buffer I this means that the pKa of the weak acid to be used in the buffer should be as close as possible to the desired pH 154 Titrations and pH Curves read over 155 Indicators read over 156 Solubility Equilibria and the Solubility Product I solubility is important I sugar and salt dissolve in water used to avor foods I fact that calcium sulphate is less soluble in hot water than cold water causes it to coat tubes in boilers reducing thermal ef ciency I consider Can at first Cans gt Ca2aq F39aq I as dissolution proceeds build up of Ca2 and F39 then have Cans gt Ca2aq F39aq I ultimately have a dynamic equilibrium Cans ltgt Ca2aq F39aq I at this point no more solid dissolves the solution is said to be saturated Ksp Ca2F39 I Ksp is termed the solubility product for the equilibrium expression RFGCSU Ch 15 Zumdahl 7th Eddoc Page 2 of 3 I now calculate the solubility of an ionic solid from the Ksp value Relative Solubilities a salt s Ksp value gives information about its solubility however must be careful in using Ksp values to predict the relative solubilities of a group of salts two possible cases I l the salts being compared produce the same number of ions I consider CaSO4Ksp 61 x 10395 gt CuIsKsp 50 x 103912 gt AgIsKsp 15 x 103916 2 the salts being compared produce different numbers of ions Bi283 AgIs Ksp 11 x 103973 gt Angs Ksp 16 x 103949 gt CuSs Ksp 85 x 103945 I see Table 155 Common Ion Effect I equilibrium shifts to the left is there is a common ion present pH and Solubility I general rule is that if A39 is an effective base there will be an increase in solubility in acid example solubility of MgOHz A39 may be a weak base or a strong base conjugate or a moderately weak or a very weak acid if A39 is not a base is a conjugate ofa strong acid then pH will have no effect on the solubility 157 Precipitation and Qualitative Analysis I will a precipitate form when two solutions are mixed I first you must recognize what the potential precipitate is most of the example and problems in the text actually tell you use ion product Q defined in the same way as the reaction quotient Q and compare it to Ksp I ifQ gtK5p ppt forms I ifQ ltK5p no ppt 158 Equilibria Involving Complex Ions omit RFGCSU Ch 15 Zumdahl 7th Eddoc Page 3 of 3
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