Close the system and insulate this very well. That or make the surroundings as hot as the cup.
a styrofoam cup. i tried it on my science project
paper
Polystyrene is a plastic. I think you meant "polystyrene foam", which would be correct.
The hot plate would heat up the salt water and cause the water to evaporate, leaving salt crystals behind. If the water vapour was led off and condensed back into water by cooling, the water would be suitable for drinking.
use insulation to keep the water hot for 40 minutes
A hot-water bottle and a cup of hot water with a slice of lemon.
syrofoam
Because heat makes plastic expand in hot water.
Well, yes, but the water must be very hot. Not just like the water temperature that we shower in.
white
No, it wouldn't. a sugar cube would melt a lot faster in a cup of Hot water. the hot water helps it desolve more evenly than cold water.
Most thermal cups are made of stainless steel or plastic. Stainless steel cups/mugs are more likely to keep drinks hot or cold longer, and are also less likely to break. They contain a layer of insulation, which may be a vacuum, or some kind of foam.