explain how salt affects the performance of sodium polyacrylate and how this relates to urine.
The correct answer and explanation is:
Correct Answer:
Salt reduces the absorbency of sodium polyacrylate by interfering with its ability to absorb water, which is relevant because urine contains salts that limit how much fluid sodium polyacrylate can retain.
Explanation (300 words):
Sodium polyacrylate is a superabsorbent polymer known for its ability to absorb and retain large amounts of water relative to its own mass. It is commonly used in products such as diapers and sanitary pads. This polymer works by using its hydrophilic (water-attracting) carboxylate groups, which allow it to absorb water and swell into a gel-like substance. The ability to absorb water is strongly influenced by the surrounding ionic environment.
When salt, such as sodium chloride, is introduced to the system, it affects the performance of sodium polyacrylate. The presence of sodium (Na⁺) and chloride (Cl⁻) ions in the solution competes with the water molecules for access to the polymer’s carboxylate groups. The ions reduce the osmotic pressure difference between the inside of the polymer and the surrounding solution. This diminished pressure difference lowers the driving force for water to move into the polymer, leading to reduced swelling and absorbency.
This is highly relevant in the context of urine, which contains dissolved salts, urea, and other waste products. The salt content in urine interferes with sodium polyacrylate’s normal water absorption process. Although sodium polyacrylate still absorbs urine, its performance is reduced compared to when it absorbs pure water. The efficiency of the polymer depends on the salt concentration: higher salt content means less water uptake and more limited swelling.
To compensate for this reduction in absorbency, commercial diaper manufacturers often use optimized formulations and additional layers to ensure effective fluid retention. Understanding how salt affects sodium polyacrylate helps in improving the design and efficiency of hygiene products in real-life biological conditions like human urination.