The Preparation of Colloid and

Electrophoresis退出

ContentContent

• Purposes and Demands • Principle• Apparatus and Reagent • procedure• Data Records and Processing • Questions• Attentions • Demonstration

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Purposes and DemandsPurposes and Demands

• Command the principle and technique of electrophoresis used to determine ζ potential.

• Determine ζ potential of Fe(OH)3 colloid by electrophoresis method.

PrinciplePrinciple

• Nearly all the colloid is electriferous. When colloid is in an electric field, electriferous particles would move to certain direction and this phenomena is called electrophoresis.

There are three reasons why colloids are electriferous.

Firstly, Colloids ionize or adsorb ions. Other reason is that triboelectricity is generated by friction between colloids and disperse medium.

Eletric potential difference between colloids and disperse medium is called ζ potential.

Obviously, in a electric field, colloids’s motion speed is related toζ potential, which is also called electrokinetic potential.

Besides, instability of colloids’s coagulation is related to ζ potential. So, ζ potential is very important for us to acquire properties of a colloid.

Given same eletric field and temperature, there is a relationship between moving rate U of colloid and ζ:

Where η is viscosity of medium, L stands for distance between two electrodes and ε is dielectric constant of medium.

• We shall be concerned with the moving boundary method to determine electrophoretic rate. If boundary between colloid and solution take t time to move distance l, we obtain:

• U ＝ l’/t

and, Eq. ① can be written in the form:ζ ＝（ ηll' ） / （ εVt ） Where l, l‘, t and V can be determined towards the exp

eriment, η can be looked up from appendix and ε can be figured out from the following formula:

T is thermodynamic temperature.

Apparatus and ReagentApparatus and Reagent

• Electrophoresis detector • Direct-current main• Stopping-watch• Funnel 1• Conductivity detector• FeCl3 （ 0.1M ）• NaCl

ProcedureProcedure• 1.     Preparation of pure Fe(OH)3

colloid.

Mete about 65 ml of Fe(OH)3 solution

and heat it nearly to boiling point. After the colloid is cooled to room temperature, distribute it into two osmotic bags,

put bags in beaker which is full of distilled water and make sure that the colloid is immersed in liquid entirely. Exchange distilled water three times and a time per 20 minutes.

2.Determination of the electrophoresis speed U and potential grads

a.Wash the electrophoresis detector with chromic acid. Scrawl the stopcock with vaseline.

b.Confect NaCl solution of which conductivity is equal to Fe(OH)3 colloid.

C. With a funnel transfer colloid to U tube until the level is above “o” scale, turn off the stopcock and then pour out splith left in U tube. Add NaCl liquor to two arms of U tube until the level is about 15 cm in height.

Carefully and slowly revolve the stopcock and make a clear boundary place between the two liquids. Put two electrodes into two arms of U tube and make sure that the electrodes height in liquids are the same.

b. Set direct-current main at 30V-50V. Mark down the position of boundary. Take records per 10 min.

d. Mete the distance between two electrodes 3-5 times and figure out an average value. (It is not the horizontal distance)

Sketch-maps of Sketch-maps of EquipmentsEquipments

Data Records and Processing• Kinds of colloid:• η ： 0.001002Pa·S• Time of eletrophoresis:• Voltage:• Distance between two electrodes:• Moving distance of boundary:• Rate of colloid:• ζ = • What charge did the colloid carry?

QuestionsQuestions

• 1.What factors does the colloid motion speed depend on?

• 2.What’s the result if the electrophoresis was not wash cleanly and some electrolyte stay on tube wall.

3.Why should conductivity of NaCl liquor be close to the colloid’s?

AAttentionttentionss

• 1.Colloid need to be osmosized as possible as pure.

• 2.Conductivity of the assistant liquor is closed to colloid’s.

3.Operate carefully and make sure the boundary is clear.