1. Determination of the Sol's CMC 退出

2. Contents  Purposes and Demands Purposes and Demands  Principle Principle  Apparatus and Reagent Apparatus and Reagent  Procedure Procedure  Data Records and Processing Data Records and Processing  Questions Questions  AttentionsAttentions 退出

3. Purposes and Demands  Acquire the method to coagulate a sol.  Acquire the method to protect a sol.  Master the determination of a sol ’ s CMC and some important rules.

4. Principle  A sol has enormous surface and strong capacity of adsorption. Fe(OH) 3 sol that is the hydrolysate of FeCl 3 in water solution could adsorb Fe 3+ ion to be positive.

5.  Kinds of sol in the same condition carry the same electric charges. A sol could exist steadily in solution because of the electrostatic repulsion.

6. Once a sol ’ s condition is changed, such as adding electrolyte, its electric charges will reduce and even eliminate. Because of the weakness of electrostatic repulsion, the sol particles will collide and coagulate with each other and become bigger. This process is called coagulation.

7. Under the certain temperature and pressure, the smallest concentration of electrolyte that can make a sol coagulate visibly is called CMC (abbreviation of Critical Micelle Concentration, the unit is mmol/L).

8. The coagulating value of CMC is due to the sol ’ s properties and states. CMC will be smaller depending on the raise of temperature, thus, sometimes we shall make a sol coagulate by rising the temperature.

9. As the temperature is certain, the value is due to the heteropolar valence of the ions that is adsorbed from the electrolyte. The heteropolar valence of the ions is higher, the value is smaller.

10. Also, the CMC of organic ions is much more bigger than the one of inorganic ions, because the adsorbing ability of the former is better than that of the latter. Adding the hydrophilic sol such as glutin can be used to keep the hydrophobe such as Fe(OH) 3 existing steady in solution.

11. Apparatus and Reagent Electric cooker glass-tube (20ml) Glass-tube frame graduated-flask (100ml) Pipette (10ml) graduate-flask (10ml) Pipette (1ml) pot bottle (150ml) Volumetric flask beaker (1000ml) FeCl 3 10% collodium NaCl 3 2.5M AgNO 3 0.1M NaSO 4 0.05M Gultin 1%

12. Procedure 1. Preparation of a sol Fill a 100ml volumetric beaker with 50ml of distilled water and heat it to boiling point.

13. Pipette 2.5ml of FeCl 3 solution to boiling water, immediately take the beaker from electric cooker to cool, and make the hydrolyzation Fe(OH) 3 prepared for standby.

14. 2. Determination of the CMC It consists of two steps in the determination. First, set out a glancing value of CMC, and then determine a further accurate value.

15. 1) Take six glass-tubes marked with “ 1 ， 2 ， 3 ， 4 ， 5 ” and “ contrast ”. Pipette 10ml of 2.5M NaCl into tube “ 1 ” and 9ml of distilled water into another five glass-tubes.

16. Then extract 1ml of liquid from tube “ 1 ” to “ 2 ”, Shaking up. And then operate up to “ 5 ” like this in turn. Exact 1ml liquid from “ 5 ” and drop.

17. Pipette 1ml of Fe(OH) 3 sol prepared into all of the six tubes hereinbefore. Shake up and record the time. Make the solution steady for 15min.

18.  Observe the coagulation in all the tubes. Compare the “ contrast ” with another five tubes and find out the coagulated tube at the latest. The concentration of this tube is the approximate value of CMC. Fill the data in the following table.

19.  Determination of CMC ’ s approximate value (C ’ ) number12345 constr ast 2.5M NaCl(ml)10.00 Distilled water(ml) 9.00 Shaking up1ml→ 1ml→ 弃去 Fe(OH) 3 sol (ml) 1.00

20. Found out the approximation of the CMC(C ’ ).

21. 2) Dilute the NaCl liquid of 2.5 mol/L to prepare the NaCl solution of C ’. Calculate the volume on the basis of the formula: C 1 V 1 =C ’ V ’. Pipette accurately V ’ ml of NaCl liquid and make up this solution in 50ml of volumetric flask.

22. 3) Take another four clean glass-tubes and mark down them with numbers “ Ⅱ、 Ⅲ、Ⅳ、Ⅴ ” and the tube of C ’ for “ Ⅰ ”. There will be a new row of six tubes including the tube of “ contrast ”.

23. Pipette in tubes of “ Ⅱ、Ⅲ、Ⅳ、Ⅴ ” respectively with 8 、 6 、 4 、 2ml of NaCl solution of C ’ and 1 、 3 、 5 、 7ml of distilled water and shake up. Pipette 1ml of Fe(OH) 3 sol into all the tubes, Shake up and make the solution steady for 15 min.

24. Then, find out the coagulated tube at the latest. Account the average value of the Cn of the latest coagulated solution with the Cn+1 of the nearby tube which has not coagulated, and the value is the CMC which can be expressed to be C=1/2(Cn + Cn+1). Finally fill in the table with experiment phenomenon and results.

25.  Determination of the CMC: number ⅠⅡⅢⅣⅤ const rast C ˊ NaCl(ml) 8.006.004.002.00 Distilled water(ml) 1.003.005.007.009.00 Fe(OH) 3 sol(ml) 1.00

26. 3. Repeat the complete procedure with electrolyte Na 2 SO 4.

27. Data Records and Processing  The CMC of Fe(OH) 3 sol coagulated with electrolyte NaCl: C ˊ = m mol/l C=1/2(Cn+ Cn+1)= m mol/l number １２３４５ⅠⅡⅢⅣⅤ C(NaCl) mmol/L coagulating

28.  The CMC of Fe(OH) 3 sol coagulated with electrolyte Na 2 SO 4 : C ˊ = m mol/l C=1/2(Cn+ Cn+1)= m mol/l The CMC ratio of using NaCl to Na 2 SO 4 is: number １２３４５ⅠⅡⅢⅣⅤ C(Na 2 SO 4) mmol/L coagulating

29. Questions  What ’ s the meaning of CMC?  What ’ s the key step in the experiment?

30. Attentions  Waste liquid is asked for callback together.  Pipettes should not be confused because each one has their respective use.

31.  Chart Ⅱ－ 20 － 1 ζpotential of Chart Ⅱ－ 20 － 2 influence of the concentration Diffuse double layer of electrolyte to ζpotential C4>C3>C2>C1 