system
Given the following post, respond as if you're commenting on Reddit:
human
Why is sodium such a good preservative?
gpt
You mean salt not sodium. Sodium is a very reactive metal. Sodium chloride is salt. In water, it separates into two particles, sodium ion and chloride ion. So two particles for every salt molecule, and so twice as much osmotic "suck", the negative pressure that pulls water out of cells. 58.5 grams of salt is one mole and in water gives two "OSMOLES'. Sugar, another common preservative, weighs 360 g/mole and only gives one particle in water (non-ionic). So, to get the same osmotic pressure it takes more than 12 times as much sugar by weight. Experiments with bacterial cells show that when the osmotic pressure surrounding the cell exceeds 8 osmolar, cell division stops, and thus does bacterial growth. This happens because water is pulled out, making the cell shrink. When it shrinks too much the DNA replication reaction doesn't have room to spin the DNA strand, necesary for chromosome duplication. Add water back, and the gyrase can work again. Cell not dead, just in suspended animation. Salt leaves food tasting salty, sugar leaves food tasting very sweet. Salt cod vs candied ginger, as familiar examples of foods preserved osmotically. Excess salt promotes high blood pressure and excess sugar promotes obesity. No free lunch, ever.