“Which component of urine (“fake”) may have the greatest effect on the absorbing power of a hydrogel polymer?”

Variables

Risks and Safety Precautions

Background Information

Dependent Variable

Controlled variables:

Independent Variable (possibilities)

What are Hydrogels?
Hydrogels are polymers that have a hydrophilic nature and are able to store water and other solvents into their large covalent lattices (Ahmed E.M, 2015). To understand this definition completely it is important to conduct research on various aspects of the definition, like conducting research into what polymers are and how substances have a hydrophilic or hydrophobic nature.

Hydrophilic/Hydrophobic Nature
A substance is hydrophilic or hydrophobic based on how it dissolves in water (2 Minute Classroom, 2016). A Hydrophobic substance cannot form any interactions with water, these molecules are typically non-polar molecules with no charges whatsoever (2 Minute Classroom, 2016). However, hydrophilic substances can dissolve and absorb water, leading them to be either covalent polar molecules or ionic lattices (2 Minute Classroom, 2016). In the case of hydrogels, it will be the covalent polar molecules that will be observed to have a hydrophilic nature.

What are Polymers?
Polymers are large covalent lattices that contain a repeating pattern of molecules, the individual unit of the repeating molecule is called a monomer (Ted-ed, 2014). Monomers in a repeating chain are all identical to one another and can repeat over a thousand times, a key characteristic of monomers is that they need to be able to bond to other molecules from both ends of its structure (Crash course, 2014).

Polymers are made through a process known as polymerisation (Cognito, 2020). There are two methods of polymeriation, addition polymerisation and condesation polymeristion (cognito, 2020).

Common examples of polymers
Polymers are seen almost everyday in human lives, they are found naturally and can be made synthetically through chemical reactions. Here are some examples of common polymers that are well known (Ted-ed, 2014):

  • DNA (Monomer: repeating nucleotides)
  • polyethylene or plastic (Monomer: ethylene)
  • Nylon (Monomers: Dicarboxylic acid and diamenes)
  • proteins (Monomers: amino acids)
  • bark from trees (monomer: cellulose)
  • fingernails (monomer: keratin)

Condensation Polymerisation
Condensation polymerisation is far more complex and requires more complex mononmers to accomplish (Cognito, 2014). Condenation polymers are created through two seperate molecules making a dimer and then eventually turning into a repeating unit of their own (Cognito, 2014). Important things about these molecules is that they both need to have two or more functional groups present their structure and the functional groups of the two molecules cannot be the same. During this process the two functional groups are broken down with free radicals in order to combine with one another (Cognito, 2014). During the creation of this bond an ester functional group is formed and a small molecule (like water) is released. The formation of the ester functional group causes all molecules formed through the condensation polymerisation to be called polyesters (Cognito, 2014).

Addition Polumerisation
In addition polymerisation the first requirment is to have an unsaturated molecule, or a molecule with one or more double/triple bonds present within it's structure (Cognito, 2020). Next the unsaturated bond is broken through the presence of what is known as a free radical, a free radical is a highly reactive molecule that contains one valence electron, allowing it to aggresively react to anything when it comes in contact (Crash course, 2014). Once the unsaturated bond is broken the carbon molecule present will now have free valence electrons on both sides of the molecule allowing it to keep bond to other nearby monomers creating a long polymer (Cognito, 2020).

How are polymers made more hydrophilic? (Crash Course, 2014)


  • Increasing the surface area to volume ratio, a higher surface area to volume ratio allows for more contact with the solvent and a higher ability to absorb it.


  • Ionic Modifications: Introduce ionic groups into the hydrogel structure. This can be achieved by copolymerizing with monomers containing charged groups (e.g., sulfonic acid groups) or by incorporating ions into the hydrogel network, which can enhance water absorption due to ion-water interactions.


Cross Linking in Polymers
Cross-Linking: Crosslinking is the process by which polymers bond to one another to create a large 3-dimensional structure (Cognito, 2020). Crosslinking allows two polymers to combine through covalent intramolecular forces rather than secondary dispersion forces (Cognito, 2020). Typically, two polymers create a three-dimensional structure through weak dispersion forces between the molecules, however, when crosslinking, an ionised beam removes hydrogen atoms attached to the carbon chain to make a direct covalent bond between the two carbon atoms that are now lacking hydrogens. The use of a covalent bond in crosslinking over the regular dispersion forces provides numerous benefits for the polymer by enhancing many physical properties, as the overall strength and cohesion of the atom are significantly increased.

Urine

The main audience for this deconstruct are babies upto the age of 3 or so (as they use nappies). Since babies are the target audience it is important to grasp how their urine differs to adult urine.

The components of urine (Ahmed et al, 2022)

Urea

Water

Creatine

Glucose

Uric Acid

Sodium Chloride (NaCl)

Inorganic salts

Ammonia

Ions (Na, K, S and many others)

Risks and Emergency Procedures

Spilling chemicals into someone's eyes. This can cause irritation and pain, if severe (for example with a highly concentrated substance) there would be even chance for blidness (Nih,2020).

Glassware breaking, causing sharp glass to be spread across the classroom. The glass can cause major cuts and bruises (Nih, 2020).

Improper disposal of chemicals. For example Hydrogel and Acids cannot be in the sink as they can cause clogging and pipe damage (Korrect Pulmbing, 2020)

Precautions

Ensure that the acids are diluted heavily with water before putting them down the sink to ensure that the solution is somewhat neutralised before being disposed (Atdsr 2022). Aside from that Hydrogels need to be dispoed in rubbish bin, not a sink, in order to prevent clogging.

If any chemical has fallen into someone's eyes, run water in your eyes to try to flood the chemicals. If you have contact lenses remove them as fast as possible and seek help from the teacher or any nearby adult (betterhealth, 2014).

If glassware has been broken ensure not to go near it, keep students away from it. If someone has been cut immediately bring this up to the teacher, or try to provide general first aid till an adult arrives

Handle all chemicals with delicacy and care. make sure not to rush as spillages and contact with skin create large amounts of swelling and pain.

Maintain a clean working environment to prevent the risk of contamination.

Same applies for handling glassware, make sure to handle with care and take things slowly in order to assure that there are no breaks and hazards

Wear Protective gear to make sure that one is safe against all kinds of spillages and breakages. Make sure that the equipment wore is not too small or worn out as it will not protect you adequately

Limitations and errors

After blood has absorbed nutrients from small intestine in the digestive system, it is transported via the renal artery into the Kidney wehre Nephrons secrete the waste product and send it down the ureter and bladder as urine (Alila Medical Media, 2020).

Firstly, baby urine is far more pure than adult urine, as adults build up certain nutrient and chemical imbalances which are reflected in their urine (Alila Medical Media, 2020)

Additionally, babies of this age have a diet that primarily consists of milk (Alila Medical Media, 2020). Since, milk is an alkaline substance with a pH of 6.5 to 6.7 the urine of babies tend to be alkaline as well (Anne Marie, 2022)

The dependent variable being measured in this case is the amount of fake urine the hydrogel can absorb.

This can be done by measuring the weight of the hydrogel after the hydrogel has been drained

Or it can be done by measuring the drained voume of hydrogel and subtracting it from the total volume added to it

Extraneous Variables

Multiple variables need to be controlled to ensure that only the independent variable is affecting the results or to ensure a fair test. These include controlling:

  • Type and source of Hydrogel powder
  • Amount of Hydrogel
  • Temperature (if not being tested)
  • pH (if not being tested)
  • The fake urine's composition
  • All the apparatus (Beakers, Sieves, measuring cylinders etc.)

The main extraneous variables are linked to environmental conditions (something that cannot be controlled). This includes:

  • Temperature in the lab (not to be confused with independent variable of temperature)
  • Humidity
  • Light exposure

Diffusion
Diffusion is the primary method in which solutions enter and exit the hydrogel (Medicosis Perfectionalis, 2019). Diffusion is the process by which substances from areas of high concentration to areas of low concentration, all through a semi-permeable layer (Medicosis Perfectionalis, 2019). In this case, the hydrogel will be the semi-permeable layer in which the fake urine will go into until equilibrium in concentration is achieved.

Temperature
Temperature is a factor that can greatly impact the absorption of hydrgoel. Firstly, an increase in temperature means an increase in kinetic energy which in-trun means the fake urine will have a higher penetrating power, allowing it to enter the hydrogel more readily (van and Westerweel, 2008). Additionally the hydrogel itself will expand and thus further swell due to the increase in temperature, thus increasing its absorption power (van and Westerweel, 2008). Lastly, the increase in kinetic energy causes the viscosity or the resistance to the flow of a solvent to reduce, allowing a more steady absorption by the hydrogel. This will be done by increasing the temperature of the urine (below the boiling point) via a bunsen burner before addiing it to the hydrgoel.

pH
The pH of the fake urine can affect the diffusion taking place for the urine to get into the hydrogel. Firstly, if the urine was acidic it would pronate some components, causing it to have a positive charge (Wu and Shanks, 2004). This positive charged ion is attracted to the partial charges in the amide function group of the polyacrylamide (the hydrogel), creating an ion dipole secondary bond and also attracting the water into the hydrogel (Wu and Shanks, 2004). The same applies to alkaline urine where the urine is depronated and has negative charge attracting to the amide group. This will be done by increasing/decreasing the amount of acidic or alkaline components in the fake urine.

Concentration of solutes (Glucose or Salt)
There are two main solutes present in the urine composition - Glucose (C₆H₁₂O₆) and Salt (NaCl). By altering the composition of these two solutes in the fake urine, it will increase the concentration causing the hydrogel's absorption to be significantly impacted. In this case the increase of solutes will cause the concentrations of solutes outside the semi-permeable hydrogel to increase, leading to a major difference in concentration between the two. The higher concentration of the outside solution or hypertonic solution allows for diffusion to occur making it very easy for the hydrogel to absorb the urine (Medicosis Perfectionalis, 2019). This will be done by adding a higher amount of solutes into the solution when preparing the fake urine

Limitations

Limitations with the apparatus/environment
The only major limitations with the apparatus is that they are not precise to an extremely high degree, however they will be more than enough to complete the practical to a high standard. The only real concern is that the lab's temperature may fluctuate causing a variability in the results, if this were controlled through the use of high level facilities more precise and accurate results will be achieved.

Limitations with the prompt
The prompt has two major limitations. The first one being that the use of fake urine does not truly reflect how real urine would react with the hydrogel, as real urine is far more complex and intricate than the fake urine made in the lab. Additionally, the use fake urine does not take into account individual nutrient imbalances or hormonal changes that could in-turn change how the hydrogel absorbs the urine

errors

Random Errors

  • Human Errors: Random errors can occur due to human factors such as inconsistent stirring techniques, variations in pouring fake urine onto the hydrogel, or differences in timing the absorption period, causing the results to have a scatter.
  • Surface Area: If the surface area of the hydrogel is different between trials it means that one trial has more hydrogel contacting the urine than the other, resulting in imprecise results.
  • Time for absorption and sieving. If the time given for absorption and sieving is inconsistent then some hydrogels will be able to absorb more urine, or there will be some remaining urine in the beaker that was not sieved. This causes each trial to have different results, introducing a scatter and imprecise results.

Sytematic Errors

  • Limitations with apparatus: If a measuring scale was damaged and had its values displaced by a certain value, then all values will be affected by this same amount, a shift in the data and all trends
  • Contamination: Contamination of the hydrogel or fake urine with foreign substances (e.g., dust particles, residues from previous experiments) can introduce systematic errors by affecting the absorption behavior of the hydrogel. This causes all the results to be affected uniformly+

Why are Hydrogels able to absorb water
Hydrogels are able to absorb water and swell up because of two primary reasons.

Functional Groups
Hydrogels have polar functional groups that can either have dipole-dipole interactions with the solvent or if applicable conduct hydrogen bonding (Dr, Masjid, 2021). The introduction of these strong intermolecular forces implies a high solvent intake from the hydrogel and the ability to retain the solvents absorbed.

Large porous 3D structure
Another aspect of Hydrogels is that in their atomic structure there are large gaps present that give the ability for water to penetrate the semi-permeable and flow into these pores (Dr.Masjid, 2021). As these pores fill the hydrogel swells further and further until it's full. The reason solvents enter is because of the osmotic pressure between the solvent and the hydrogel itself (as the solvent would want to achieve equilibrium being of a higher concentration) (Dr.Masjid, 2021). Once the osmotic pressure between the hydrogel and the solution around it is balanced there won't be anymore urine absorbed. Furthermore, cross-linked hydrogels are able to absorb far more urine than regular hydrogels (Dr.Masjid, 2021). Crosslinking allows for primary bonds to hold together the many polymer chains rather the use of weak secondary bonds. This allows for the hydrogel to be able to absorb and retain more urine (Dr.Masjid, 2021).