Net ionic equations (NaOH; HCl; H2O)

[berry2]

Hi,

I completed a Grade 12 experiment and now I am doing some calculations about it but I am confused.

Here is the question: "Write the net ionic equation for each reaction, and note the value of ΔH for each reaction. e.g. H⁺(aq) + OH^-(aq) --> H₂O(l)
ΔH = -45 kJ/mol HaOH
I had three reactions.
1. Heat of dissolution of NaOH; 200 mL of labelled water + 5.5 g of crystal NaOH

2. Heat of reaction between aqueous NaOH and aqueous HCl; 100 mL of 1.0 mol/L HCl + 100 mL of 1.0 mol/L NaOH

3. Heat of reaction between solid NaOH and aqueous HCl; 200 mL of 1.0 mol/L HCl + 5.5g of crystal NaOH

These were the instructions also given: "Since all the solutions are dilute, then the density of each solution can be assumed to be 1.00 g/mL. So, 100 mL has a mass of 100 g."

So for the first reaction, would the net ionic equation be something like this:
1. 200 g H₂O(l) + 5.5 g NaOH(s) --> I don't know what the product would be?
2. 100 g HCl(aq) + 100 g NaOH(aq) --> NaCl + H₂O?
3. 200 g of HCl(aq) + 5.5 g NaOH(s) --> NaCl + H₂O?

Any help would really be appreciated!
Thanks

 

[Borek]

Whenever you are told to write the net ionic reaction you should start by writing every dissociated substance as ions - so not NaOH(aq), but Na⁺(aq) + OH^-(aq) and so on. Then cancel ions whenever they appear in the same quantity on both sides of the balanced equation.

In the first reaction you have NaOH(s) on the left, so the reaction is just that of a dissociation. Two other reaction equations are OK.

Other than that it is difficult to help, as you didn't give us complete information, and the information you gave is a bit confusing: you wrote you had "reactions", but apparently the experiment was about enthalpy changes, so you are either expected to calculate expected temperature change, or you measured the temperature change and you are expected to use the data to calculate ΔH. Note that these are actually limiting reagent problems - masses given suggest you are expected to calculate amount of substances that reacted.