电导法测定弱电解质电离常数及难溶盐溶解度

So, ionization expressed as:
constant
could
be
Kc
c 1
2
Ionization degree α in formula ① is related with molar conductivity. That is: o
K 1 1000 c
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.
Conductivity detector Super thermostatic trough Conical flask （250ml） Conical flask （50ml） Pipette (20ml) Beaker (100ml) 0.1000M HAc solution CaSO4(A.R) 1 1 2 3 2 1
Λ——molar conductivity when concentration is c Λ 0——ultimate molar conductivity if solution
is diluted illimitably sum of positive and negative ion molar conductivity) can be lookup on literatures.
1 c Kc o Kc
2 o
④
Draw a graph of cΛ m against 1/Λ and get a beeline of which slope is: slope = Λ 0 2 × Kc Look for Λ out Kc.
0
on literaቤተ መጻሕፍቲ ባይዱures, and account
Content
Purposes and Demands Principle Apparatus and Reagent procedure Data Records and Processing Questions Attentions Demonstrated
Purposes and Demands
Procedure
1 ） Determination of weak electrolyte ionization constant 1. Regulate the temperature of thermostatic trough at 25℃±0.1℃. Put 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.
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.
Principle
1 ） Determination of weak electrolyte ionization constant. At certain temperature, the equilibrium of acetic acid ionization in water can be written as follow HAc = H+ + Ac－ Initial c 0 0 eg c(1-α ) cα cα
2 ） Determination of dissolved salt’s solubility
Kc = Ksolution – KH2O
hardly
Ksolution —— conductivity of solution
KH2O —— conductivity of water
Apparatus and Reagent
2. Clean a platinum black electrode with distilled water and blotted it up by the use of filter paper (don’t touch platinum -black). Put the electrode into the conical flask filled with 40ml HAc and detect the conductivity.
1. To determine the ionization constant of acetic acid. 2. To determine the solubility of calcium sulphate. 3. Master the operation of conductivity detector.
Λ0 = L++ L–（the
K —— conductivity (s/cm or ms/cm orμ s/cm). It can be determined through experiment. C —— concentration (mol•L-1 or N • L －1)
实验原理
Adding equation .② into .①, we obtain that