Re: Which could be the applications of adding salt to water?

Hi Maria,

Salt water, of course, makes up about 71% of the Earth’s surface – all 
those oceans are salty!  This has some very important consequences for all 
life on earth.  You’ve already found out that by adding salt to water you 
increase its boiling point – but what does this mean for life?

Water can exist in 3 states or phases (see this phase diagram).  By this I mean 
that we commonly find water in a gaseous phase (steam), a liquid phase (water) 
and a solid phase (ice).  It takes energy to cause liquid water to change into 
gaseous water – energy supplied when you heat up water.  Heat is a common form 
of energy.  When you heat water enough, water changes into steam. 

If you look at it another way, say you are collecting pennies in your 
piggy bank. You know that your piggy bank holds 100 pennies. You also know 
that if you collect 100 pennies that equals a dollar.  So you slowly add 
pennies until the bank is full.  Then you can take you piggy to your Mom 
and she’ll give you a dollar.

When you add heat to water, it is like adding pennies to the bank.  After 
a certain point (the boiling point) you’ve added enough heat to cause the 
water to change into gas (steam) (or enough pennies to change into a 
dollar).  

When you add salt to your water it’s like increasing the size of your 
piggy bank, slightly (by two or three pennies).  Which means that it takes 
more heat to make the water boil (as you found out).  In the oceans (where 
there is a lot of water), it means you can store a lot more heat, before 
it turns into gaseous water (steam).  Heat storage in the ocean is linked 
to weather – which in turn affects all life.

Here is a great site to practice what the weather would be like if by 
affecting salt water:

http://www.pbs.org/wgbh/nova/elnino/anatomy/earthsweather.html 

Salt water is not always beneficial to life.  A problem for animals living 
in salt water is known as osmosis.  Osmosis is the movement of water back 
and forth across a membrane.  A membrane is anything that controls the 
flow of something.  For example, if you wanted to pour a pitcher of water 
and ice through a dish towel, only the water would go through – not the 
ice.  The ice doesn’t go through because it is too big to pass through the 
membrane – the dish towel.  Salt water causes water to flow out of an 
organism into the water – making the organism shrivel – which isn’t so 
great if you are an animal.  Look at this web site about os
mosis: the blue dots are water molecules that move across the membrane (the 
black line) to balance the green dots that are salt.  You can see that the 
container on the left ends up with much more water than it began with, leaving 
the container of water on the right very low.  When an organism doesn’t have 
enough water – it is dehydrated, which means the animal won’t work right.
So, adding salt to water can be a very good thing, especially for weather, 
but it can also be a dangerous thing for an animal – causing dehydration.

Here’s another experiment with salt water – add salt water to ice and add 
fresh water to ice – which melts fastest?  Be sure to predict what you 
think might happen first.  Then try it!