Re: how much salt is needed for water not to freeze?

G'day Jennifer.

You cannot totally stop water from freezing by adding salt -- you can only make it harder to 
freeze. What salt does is to lower the freezing temperature of water. The more salt you add, the 
lower the temperature. Here are a few values to give you the general picture:

Ordinary water freeezes at 0.0 deg C
1% salt solution (10.1 g of salt per litre of solution) freezes at -0.6 deg C
3% salt solution (30.6 g of salt per litre of solution, approximately equal to ocean water) freezes at 
-1.8 deg C
5% (51.7 g/L) freezes at -3.0 deg C
10% (107.1 g/L) freezes at -6.6 deg C
15% (166.3 g/L) freezes at -10.9 deg C
20% (229.6 g/L) freezes at -16.5 deg C
23% (269.6 g/L -- saturated) freezes at -20.7 deg C

These data are taken from the CRC Handbook of Chemistry & Physics, Edition 56, pages D252-
253.

It doesn't take much salt to stop things freezing in Sydney. On a good cold winter's day in parts of 
Canada or Siberia, no amount of salt will help much!