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Dialysis – Purification of Colloids, Dialysis, Electrodialysis, Practice Problems and FAQ

Dialysis – Purification of Colloids, Dialysis, Electrodialysis, Practice Problems and FAQ

We are aware that a functioning kidney cleans our blood and excretes extra fluid through urine. They also secrete a variety of hormones that are essential for our bodies to function normally.

What would occur if your kidneys were unable to remove enough fluid and waste from your blood?

This usually happens when your kidney function is about 10% to 15% or less. There may be a sizable number of waste products in your blood that are extremely harmful to your body.

What actions are appropriate in this situation?

Using a dialyser, a procedure known as "hemodialysis" is performed to purify your blood. The term "artificial kidneys" is frequently used. This therapy is based on the dialysis procedure.

On this concept page, we will get to know more about dialysis, electrodialysis and its uses.


  • Purification of Colloidal Solutions
  • Dialysis
  • Electrodialysis
  • Application of Dialysis in Kidney Failure
  • Practice Problems
  • Frequently Asked Questions – FAQ

Purification of Colloidal Solutions

Colloidal solutions contain excessive amounts of electrolytes and dissolved impurities that can cause the sols to become unstable. Therefore, colloidal solutions are stabilised by removing these contaminants. The removal of these contaminants or the purification of the colloidal solution can be done by the following methods.

  1. Dialysis
  2. Electrodialysis
  3. Ultrafiltration
  4. Ultracentrifugation


“The process of separating the particles of a colloid from crystalloids by means of diffusion through a suitable membrane is called Dialysis”

A material that forms a real solution and diffuses across a membrane through dialysis is referred to as a crystalloid. The idea behind it is that while ions from an electrolyte or crystalloids can travel through a barrier made of parchment or cellophane, colloidal particles cannot. The colloidal solution is carried in a cellophane or parchment bag. In fresh water, the bag is submerged. A purified colloidal solution is left behind as the contaminants gradually diffuse out of the bag.

The distilled water is replaced on a regular basis to avoid crystalloid aggregation, which could cause them to diffuse back into the bag. The HCl in the ferric hydroxide sol can be removed by dialysis.


Dialysis is a slow procedure; its speed is determined by the differences in particle size and the uneven diffusion rates between crystalloids and colloids.

“The dialysis procedure uses an electric field to speed up the purification process. It is known as electrodialysis”

Electrodialysis, which involves providing an electric field while the crystalloids are charged, can influence the rate of dialysis. The sort of dialysis in which electrodes are attached to the membrane's sides is known as electrodialysis. This membrane allows positively charged ions to pass through one side while permitting negatively charged ions to pass through the other. The process of dialysis is accelerated as a result.

Application of Dialysis in Kidney Failure

Dialysis is used to treat kidney damage via a technique called hemodialysis.

“Hemodialysis involves drawing blood, purifying it through dialysis, and then reinjecting it back into the body”

Salts, water, urea, and metabolic acids are all retained in kidney failure. The patient is then attached to a hemodialyzer, another name for a dialysis machine. Small channels composed of semipermeable membranes allow the blood to flow across them. To the sterile solution, substances like sugar and amino acids are added. The molecules pass through the membranes as they are on the other side of the dialysis solution. The molecules move through a region of low concentration from one of high concentration.

Practice Problems

Q1. Which of the following techniques are used for the purification of colloids?

A. Ultrasound
B. Ultrapeptization
C. Ultracentralisation
D. Ultrafiltration

Answer: D

Solution: Colloidal solutions can be stabilised by eliminating the excess electrolytes and the dissolved impurities. Dialysis, electrodialysis, ultracentrifugation, and ultrafiltration are the methods that are frequently used to purify colloidal solutions. Hence, out of the given option, ultrafiltration is the right one.

So, option D is the correct answer.

Q2. What kind of particles are able to cross the semi-permeable membrane used in the dialysis process?

A. Electrolytes
B. Crystalloids
C. Particle size distribution less than 1 nm
D. All of these

Answer: D

Solution: The process of separating the particles of a colloid from crystalloids by means of diffusion through a suitable membrane is called dialysis. While colloidal particles cannot pass through a barrier constructed of parchment or cellophane, ions from an electrolyte or crystalloids can. The particle size of the crystalloid is less than 1 nm. Hence, all the given options are correct.

So, option D is the correct answer.

Q3. What would happen to the colloidal solution if it experienced excessive purification?

A. The quality of the colloidal solution is increased to the next level
B. The excessive purification will change the particle size of the colloidal solution.
C. Excessive purification will lead to the coagulation of colloidal solution.
D. Purification is possible up to a point. After then, the solution won't respond to the process.

Answer: C

Solution: If the colloidal solution experience excessive purification, it will remove the minimum of electrolyte too and hence, the colloidal solution becomes unstable and leads to coagulation.

So, option C is the correct answer.

Q4. Which kind of membrane should be used in the dialysis process?

A. Parchment Paper
B. Animal Membrane
C. Cellophane
D. All of these

Answer: D

Solution: Only membranes that allow a real solution made up of ions or smaller molecules and not colloidal particles to pass through them can be employed. Therefore, parchment paper, animal membrane (bladder), or cellophane sheets are employed for this purpose.

So, option D is the correct answer.

Frequently Asked Questions – FAQ

Q1.  Are osmosis and dialysis the same process?
No, osmosis and dialysis are similar processes but not the same process. The diffusion of a solvent through a semipermeable membrane in osmosis and the diffusion of crystalloids or electrolytes through a semipermeable membrane in dialysis is the similarity. But, the difference is in the diffusion of different particles.

Q2. Does hemodialysis actually help a patient with kidney failure?
Hemodialysis is a procedure that benefits a lot of kidney failure patients because kidney failure puts the patient at considerable risk since total renal failure requires a kidney transplant within two weeks or the patient will die. The hemodialyzer is extremely beneficial in the battle against death until the patient finds a suitable kidney for donation.

Q3. Can you resume kidney function after dialysis?
Acute kidney failure needs to be treated right away and is frequently reversible. Following the treatment of the actual reason, the kidneys typically begin to function normally again within a few weeks to months. There must be dialysis until then. Therefore, prompt medical attention and hospitalisation may help restore kidney function if you experience acute kidney failure. But kidney transplantation is the only option if you have a situation of complete kidney failure.

Q4. Which membrane is utilised in dialysis?
Dialyzers are currently produced using three different membrane types: synthetic noncellulose, substituted cellulose, and cellulose. Cuprophan, the most common form of produced cellulose, is a polysaccharide-based membrane made from pressed cotton.

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