Why does the mass of a polysaccharide increase when linking monosaccharides?

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Discussion Overview

The discussion focuses on the mass change of polysaccharides, specifically starch, when linking monosaccharides like glucose. It explores the chemical process involved in polymerization, including the removal of water molecules and the resulting mass calculation.

Discussion Character

  • Technical explanation

Main Points Raised

  • One participant explains that the final mass of a polysaccharide is calculated as n times its empirical formula plus a water molecule, referencing the example of starch from glucose.
  • Another participant clarifies that the water from each monosaccharide is already accounted for in the initial formula, suggesting that one additional water molecule should be added due to the structure of the polymer.
  • A third participant emphasizes the importance of counting atoms in understanding the mass change.

Areas of Agreement / Disagreement

Participants provide differing perspectives on the mass calculation, indicating that there is no consensus on the exact reasoning behind the mass increase when linking monosaccharides into polysaccharides.

Contextual Notes

The discussion does not resolve the assumptions regarding the initial mass of the monosaccharides or the implications of the structural changes during polymerization.

Shakattack12
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Hey guys. When a polysaccharide (e.g. starch) is made I understand that monosaccharides are linked together and a water molecule is removed. In the final product the polysaccharide has a mass of n times its empirical formula plus a water molecule. Like the mass of 300 starches from 300 glucose molecules is 300(C6H10O5) + H2O. Why is this?
 
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I think you mean why a starch molecule from 300 glucose molecules is 300(C6H10O5) + H2O.

Because the water from each molecule has already been subtracted [the molecule of monomer was initially (C6H12O6)]. You must add one water molecule because the polymer has an -OH in the one end and -H in the other end.
 
It is all in the structure - just count the atoms:

starch.png
 

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Thanks guys you were extremely helpful!
 

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