Great question, Lyana!  There are several different ways you can produce heat:

1.       You can focus the sun’s rays using a magnifying glass, but watch where you point the focused beam of light because it can set things on fire!

2.       You can use friction—by rubbing two objects together, the friction between them creates heat.  You can prove this to yourself just by rubbing your hands together; as you rub them together they will begin to feel warm.

3.       You can use chemicals to create heat.  As some chemicals dissolve in water, they give off heat.  This is called an exothermic reaction.  One such chemical is magnesium sulfate (MgSO4), which you can purchase inexpensively on the internet (http://www.ebay.com/itm/like/280605941369?lpid=82)

I would suggest you use the chemical approach, and ask your parents to help you purchase some MgSO4, and dissolve about ½ cup of it in 1-2 cups of water in a plastic bottle.  Shake the bottle well to dissolve the MgSO4.  Have your teacher and classmates touch the bottle, and feel how warm it gets (be careful—it could get very warm!).


For more information about exothermic chemical reactions, please visit http://en.wikipedia.org/wiki/Exothermic_reaction

Great question!  There are a lot of really good chemical reactions that a 9-10 year old could demonstrate to a class safely.  The question is which one is likely to be new to the crowd.  For your daughter I'd recommend the "Invisible Ink" reaction:

http://discoveryexpress.weebly.com/homeblog/invisible-ink-how-acid-and-heat-can-reveal-messages

You will use lemon juice (acid) and a clothes iron set at its highest setting (heat) to demonstrate how the acid in the lemon juice breaks down the cellulose in the paper to more combustible compounds.  She could even go on to use other compounds, as suggested in the exercise.

A few others you could try:

http://discoveryexpress.weebly.com/homeblog/what-is-solubility

http://discoveryexpress.weebly.com/homeblog/use-vinegar-and-baking-soda-to-blow-up-a-balloon

That's a great question, Vansh.  First we have to discuss how water is purified.  There are several different ways to purify water--that is, to take any salts, solids, microorganisms, or anything else you would not want to drink out of the water.  One way is to filter it, or to pass it through a physical barrier which allows the water through, but holds most of the bad things back.  Depending on the filter, some things in the water may be small enough to pass through, like salts or viruses.

Another way is to add chemicals, like chlorine or ozone, to the water, or bombard the water with ultraviolet radiation.  These methods will kill microorganisms that could make you sick.  This will make most water safe to drink, but will not remove large solids like dirt.

Another way to clean up water for drinking is to distill it, or to cause it to vaporize away from the other things contaminating it.  In this process you heat up the water, causing it to form steam.  The steam rises away from the other things in the water like salts or microorganisms (which do not vaporize).  When the steam lands on something cold it will condense to form water again, but this water does not carry the same solids as the water before.  If you can collect this water in a container like a bowl or bottle, it should be much cleaner than the original water, and hopefully safe to drink! 

NOTE:  If you try this with water from your kitchen sink, the filtered or distilled water will very likely be good to drink.  However, if you try this with murky lake or pond water, I don't recommend drinking it after only one filtration or distillation!!  Sometimes water can hold dangerous viruses that a filter will not remove, and some of the dirty water could splash during distillation, putting some microorganisms in your clean water. 


We found a great website that shows how to make a filter that uses cotton, gravel and sand, and an empty plastic water bottle.  Please visit Instructables.com to see how they made their simple water filter.  This one would be very good for a school project!

We also tried making a water distillation system ourselves using a pot of boiling water on a stove, a large pot lid, a bowl, and a bag of ice.  You assemble the system as in the figure below:

Put the pot on the stove to boil the water, place the lid on the top at an angle, so the lid slopes downward to the bowl.  Put the bag of ice on top of the lid, and watch as clean water drips into the bowl! 

We tried this, and it worked well!  Please watch our YouTube video and see!

First off, molarity is just a way of expressing the concentration of a solution.  The molarity is the number of moles per liter of solution.  A mole is defined as 6.022 x 1023 (also called Avogadro’s constant) molecules—that’s basically a six with 23 numbers behind it!    

Secondly, every element or molecule has a molecular weight, or a mass per molecule of that compound. 
For example, sodium chloride—NaCl—has a molecular weight of 58.443 grams per mole.  This is, conveniently, also the number of grams per mole of this compound. Therefore, one mole of sodium chloride will weigh 58.443 grams.  

Finally, if you know how much of your sodium chloride is in the solution, and you know how much liquid it is dissolved in, you can find the molar concentration.  
 
Here’s an example:  
 
You have 26 grams of NaCl dissolved in 0.6 liters of water.  What is the molarity?


We know that NaCl is 58.443 grams per mole, and that we have 0.6 liters of water.  We need to find
how many moles of NaCl there are per liter of water to get the molarity.  Here is how we set the problem
up:

So the final answer is 0.742 molar (M) NaCl.

A: Thanks for the question James!  Ice floats because when water freezes (that is, when the temperature drops below 32 degrees Fahrenheit or 0 degrees Celsius) it becomes less dense than when it is in its liquid form.  That is, if you had a cup of water and a cup of ice, there would be less “stuff”—fewer water molecules—in the cup of ice than the cup of water.  The reason this happens is because of water’s hydrogen bonds.

Each molecule of water is made of one oxygen atom and two hydrogen atoms which look like this. This is why we can also write ‘water’ as ‘H2O’.

The oxygen atom of one molecule will be attracted to a hydrogen atom on another molecule.  This attraction is called a hydrogen bond, because once it is formed it is not too easy to pull the molecules far away from each other (and, of course, because it involves hydrogen!).

When the water is a liquid, these hydrogen bonds are fairly flexible, allowing
the water molecules to slide past each other.  However, when the water freezes
the hydrogen bonds become less flexible, and they hold the water molecules
farther away from each other than they would if they were liquid. Because the
molecules are held farther away from each other, there are fewer of them in a
cup than there would be in a cup of liquid water. This is what makes the ice
less dense, and is the reason why the ice floats on top of liquid water!