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1、电导法测定弱电解质电离常数电导法测定弱电解质电离常数及难溶盐溶解度及难溶盐溶解度DeterminationofWeakElectrolyteIonizationConstantandsolubilityofHardlyDissolvedSaltbyConductivityMethods Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd. ContentPurposes and Demands PrincipleApparatus and Rea
2、gent procedureData Records and Processing QuestionsAttentions DemonstratedEvaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Purposes and Demands1. To determine the ionization constant of acetic acid.2. To determine the solubility of calcium sulphate
3、.3.Master the operation of conductivity detector.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Principle1） Determination of weak electrolyte ionization constant. At certain temperature, the equilibrium of acetic acid ionization in water can be w
4、ritten as follow HAc = H+ + AcInitial c 0 0eg c(1-) c cEvaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.So, ionization constant could be expressed as:Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyL
5、td.Ionization degree in formula is related with molar conductivity. That is: molar conductivity when concentration is c 0ultimate molar conductivity if solution is diluted illimitably0=L+L（the sum of positive and negative ion molar conductivity) can be lookup on literatures.Evaluationonly.Createdwit
6、hAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.K conductivity (s/cm or ms/cm ors/cm). It can be determined through experiment.C concentration (molL-1 or N L1)Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Adding equat
7、ion . into ., we obtain thatDraw a graph of cm against 1/ and get a beeline of which slope is:slope = 0 2 KcLook for 0 on literatures, and account out Kc.实验原理Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.2）Determination of hardly dissolved salts
8、 solubility Kc = Ksolution KH2OKsolution conductivity of solutionKH2O conductivity of waterEvaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Apparatus and ReagentConductivity detector 1Super thermostatic trough 1Conical flask （250ml） 2Conical flask
9、（50ml） 3Pipette (20ml) 2Beaker (100ml) 10.1000M HAc solutionCaSO4(A.R)Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Procedure 1） Determination of weak electrolyte ionization constant 1. Regulate the temperature of thermostatic trough at 250.1. P
10、ut two conical flasks one of which is filled with 120-130ml conductive water and another with 40ml HAc(0.1M) into thermostatic trough, and maintain the temperature at this level for 20 min.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.2. Clean a
11、 platinum black electrode with distilled water and blotted it up by the use of filter paper (dont touch platinum -black). Put the electrode into the conical flask filled with 40ml HAc and detect the conductivity.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011
12、AsposePtyLtd.Remove l of HAc solution and complement with 20ml conductive water that has been kept temperature constant, shaking up. After temperature is kept constant for 5 min, determine the conductivity of the solution above. Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.C
13、opyright2004-2011AsposePtyLtd.Repeat the same dilution procedure to confect other five HAc solution of different concentration showed in the table below.Determine six conductivities of these solutions and complete the table.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyri
14、ght2004-2011AsposePtyLtd. 2）Determination of hardy dissolved salts solubility1. Weigh 1g CaSO4 solid, put it into 100ml beaker and dissolve with distilled water. Heat the solid-liquid mixture up to boiling point. Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-201
15、1AsposePtyLtd.Drop off superstratum liquid. Repeat the same procedure twice and think about the meaning of this operation.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.2. Dissolve the solid adequately with 80ml distilled water and heat it up to
16、boiling point. Cool the liquid down to room temperature, collect clear topper liquid and take it to thermostatic trough. Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Fill the beaker with 40ml distilled water. Repeat the above procedure twice. W
17、hen the temperature keeps constant, measure the conductivity of these three saturated CaSO4 solutions.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.3. Get 40ml of conductive water which has been kept temperature constant and measure its conducti
18、vity. Figure out the conductivity of CaSO4 by the formula we have learned.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.（1） Determination of weak electrolyte ionization constant by conductivity methodsData Records and ProcessingEvaluationonly.Cr
19、eatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Draw a graph of cm against 1/ and calculate its slope.And as we know: +0（ literatures） 349.8 40.9390.7(-1cm-1mol-1)Then, Kc would be figure out, that is Kc =Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProf
20、ile5.2.0.0.Copyright2004-2011AsposePtyLtd.实验数据记录和处理2 2）Determination of solubility of hardly dissolved salt Determination of solubility of hardly dissolved salt 1. Conductivity of water1. Conductivity of watertimes123averagerConductivityofwater（Scm-1）Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5
21、ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.实验数据记录和处理2. conductivity of CaSO4 saturated solutiontimes123averageconductivityofCaSO4（Scm-1）Kcaso4=Ksolution-KwaterEvaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Questions1. Why should we use t
22、he thermostatic trough in the experiment?2. Why cant we determine conductivity of solution with direct current?3. Why do we have to wash CaSO4 solid and use superstratum liquid for determination in the preparation process of CaSO4 saturated solution?Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5C
23、lientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Attentions1. Conductance electrode must be below liquid-level.2. Determination must be operated in constant temperature.3. Conductivity detector must be proofread before each determination.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfi
24、le5.2.0.0.Copyright2004-2011AsposePtyLtd.Outline in the use of DDS-11A conductivity detector1. Switch on the electrical source and allow it warm-up for several min (until pointer turns stable).2. Turn the constant knob to be electrode constant (its been checked and determined by the factory).Evaluat
25、iononly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.3.Emendation. Determine conductivity of H2O on low round and HAc is on high round. Turn the knob, driving the pointer point to full scale namely 1.0.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientPr
26、ofile5.2.0.0.Copyright2004-2011AsposePtyLtd.4. Determination. Choose proper measuring range from large range to small one and try to control the pointer pointing to the full scale in order to get accurate data. That just is: 1041031021010.1 Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProf
27、ile5.2.0.0.Copyright2004-2011AsposePtyLtd.5. Reading and record. The data marker is in the form of 10x10-6(s/cm). X stands for 4 , 3 or 2 and 1 in the measuring range.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.Evaluationonly.CreatedwithAspose.Slidesfor.NET3.5ClientProfile5.2.0.0.Copyright2004-2011AsposePtyLtd.
