Thread: y NaCl is more effective than sucrose in lowering Aw?

why is salt more effective than sugar in lowering water activity?
All the webby kept saying that salt have higher water binding capacity.. but doesn't states why.. I've been searching the net for like an hr.
cause a+ binds to 6 H20 and Cl- binds with 5.. and they are ionic bond... that's what i find out only.. but how to compare with sucrose?

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Explain what you mean by "water activity."

Water activity or aw is a measurement of the energy status of the water in a system. It is defined as the vapor pressure of water divided by that of pure water at the same temperature.
There are several factors that control water activity in a system. Colligative effects of dissolved species (e.g. salt or sugar) interact with water through dipole-dipole, ionic, and hydrogen bonds. Capillary effect where the vapor pressure of water above a curved liquid meniscus is less than that of pure water because of changes in the hydrogen bonding between water molecules. Surface interactions in which water interacts directly with chemical groups on undissolved ingredients (e.g. starches and proteins) through dipole-dipole forces, ionic bonds (H3O+ or OH-), van der Waals forces (hydrophobic bonds), and hydrogen bonds. It is a combination of these three factors in a food product that reduces the energy of the water and thus reduces the relative humidity as compared to pure water. These factors can be grouped under two broad categories osmotic and matric effects.
Basically, water activity is one of the determinants in the shelf life of a food product base on available water for the possible chemical, biological and physical reaction or damage to the food like enzymatic browning, lipid oxidation, hydrolytic reaction, moisture content Isotherm etc etc..

Colligative effects of dissolved species (e.g. salt or sugar) interact with water through dipole-dipole, ionic, and hydrogen bonds

well NaCl has strong ionic bonds and so perhaps this will effect the water activity more than glucose

If it's a colligative property like you said, NaCl will have more of an effect since it breaks into two particles and sucrose stays one.