Science Buddies: "Ask an Expert"

So I am doing this chemistry project for grade 9. It is called a cool pack.
Here are the materials.
Sodium bicarbonate (baking soda) - 5ml
Citric acid -5ml
Teaspoon (to measure 5ml)
Zip-lock plastic bag
Water - 5ml
So basically I am mixing Baking soda and citric acid in a ziplock bag. First step is to mix those 2, record what is happening and what it feels like. I add a little bit of water, and i observe and touch the bag again.
Can anyone help me clarify what the reactants and products are.
ReactantsCitric acid, Baking soda
ProductsCarbon dioxide and sodium citrate
I have done some research and it says water is formed in experiment. So is water a reactant and a product or one of those 2 or neither at all?
Thank you.

Hi,

When you add water, you allow the baking soda (sodium bicarbonate) to disassociate into its constituent ions, Na+ and HCO3-, since sodium bicarbonate is soluble. This allows the reaction between the baking soda and the citric acid to proceed. Therefore, when you add water, you are basically making a sodium bicarbonate solution, so in the chemical equation the reactant would be represented as NaHCO3(aq) - aq stands for aqueous, another word for in solution. Water, however, is formed during the reaction, so it is a product. I hope this helps!

Elena

cumulonimbus wrote:Hi,

When you add water, you allow the baking soda (sodium bicarbonate) to disassociate into its constituent ions, Na+ and HCO3-, since sodium bicarbonate is soluble. This allows the reaction between the baking soda and the citric acid to proceed. Therefore, when you add water, you are basically making a sodium bicarbonate solution, so in the chemical equation the reactant would be represented as NaHCO3(aq) - aq stands for aqueous, another word for in solution. Water, however, is formed during the reaction, so it is a product. I hope this helps!

Elena

Hi, thanks for the reply. So water is a product, but is water a product too?
Thank you.

Hi AngekNoakPardk,

Water has an important function in this chemical reaction: the solvent. It's the medium in which the reactants and products move around. And, as Elena noted, it lets the ionic "pieces" of the reactants move around.

For example, Imagine Na+ in water. This ion is stabilized by the oxygen parts of water. Water is polar, the oxygen end has a partial negative charge. These little partial negative charged parts surround the positive Na ion, stabilizing it. The ones closest to the Na+ are considered to be the "solvation shell" of the sodium ion.

As for the reaction, you'll need to consider writing the equation:

NaHCO3 + H[citrate] --> Na[citrate] + CO2 + HOH

Yes, the HOH is water... but I wrote it HOH so that you can see where it came from. The bold H is from the citric acid. Take away a CO2 from HCO3 and that leaves OH. H + OH = HOH

That's why water is a product. We usually won't write the solvent as a product or reactant since it's just "hosting" the reaction and will appear in equal quantities on each side. (So it just cancels out.) However, in this case, you can see above how we're actually generating more water.

Hope this clears it up a bit.

-John