how much salt must I put into a 100mls of water to stop it freezing when left overnight in a home freezer
That depends upon the temperature setting of your freezer. It is adjustable, you know. A recommended setting is 0 F (-18 C)
I suggest you calculate the freezing point depression of a fully saturated solution of NaCl. That will tell you how high the temperature setting will have to be, to prevent freezing.
It turns out that you can reduce the freezing point to as low as -21 C with a fully saturate salf solution.
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To determine the amount of salt you need to add to prevent the water from freezing when left overnight in a home freezer, we need to understand that salt lowers the freezing point of water. In other words, it makes it harder for the water to freeze.
The exact amount of salt required depends on the concentration of the salt solution. The more salt you add, the lower the freezing point of the water will become. Here's a basic guide to get you started:
1. Find the desired freezing point: Determine the temperature at which you want the water to remain unfrozen. Let's assume you want it to stay liquid at -10°C.
2. Look up the freezing point depression constant: This constant varies based on the type of salt you use. For sodium chloride (table salt), the constant is approximately 1.86°C/m, meaning that for every 1 gram of salt dissolved in 1 kilogram of water, the freezing point is lowered by 1.86°C.
3. Calculate the molality: Molality is the number of moles of solute (salt) per kilogram of solvent (water). To calculate the molality, divide the mass of salt (in moles) by the mass of water (in kilograms).
4. Convert milliliters (ml) to kilograms (kg): There are 1000 grams in a kilogram, so divide the volume of water (in milliliters) by 1000 to get the mass in kilograms.
5. Determine the mass of salt needed: Multiply the molality by the mass of water in kilograms to get the mass of salt required.
Once you have all these values, you can calculate the amount of salt needed to prevent the water from freezing at the desired temperature. Remember, this is just a rough guide, and actual results may vary based on factors such as impurities in the water and the efficiency of your freezer.
Alternatively, you can use online salt concentration calculators or consult scientific references to determine the specific amount of salt needed to achieve your desired freezing point.