How do i calculate the concentration of carbonic acid?I am doing a chemistry experiment investigation that models the formation of acid rain.
The experiment involved producing carbon dioxide and bubbling it through distilled water to produce dilute carbonic acid. To produce the carbon dioxide i reacted sodium carbonate with hydrochloric acid. I have complete the following calculations so far:

Balanced molecular:

2HCl (aq) + Na2CO3 (s) -> 2NaCl (aq) + CO2 (g) + H2O (l)

Ionic equation:

2H+ (aq) + Na2CO3 (s) -> 2Na+(aq) + CO2(g) + H2O (l)

Initially the number of moles of sodium carbonate and hydrochloric acid must be calculated to determine the limiting reagent:

n (Na2CO3) = ?

m= 9g

M= (22.99 x 2) + 12.01 + (16x3)

= 105.81 g.mol-1

n=

=

=0.08505812305 mol

n (HCl)= ?

m= 50mL

1mL = 1g

∴m=50g

M = 1.008 +35.45

=36.458 g.mol-1

n=

=

= 1.37144111 mol

The stoichiometric ratio between the hydrochloric acid and sodium carbonate is as follows:

HCl: Na2CO3

2:1

Therefore approximately…

0.08505812305mol x2 of HCl is required to react with Na2CO3

= 0.1701162461mol

The hydrochloric acid is in excess therefore the sodium carbonate limits the amount of product produced and is the limiting reagent.

Therefore the number of moles of carbon dioxide produced can be calculated as follows:

n(CO2)= ?

= n(Na2CO3) (as the stoichiometric ratio is 1:1)

= 0.08505812305 mol

I was wondering waht to do next if i am to calculate the concentration of carbonic acid?

Expert Answers

| Certified Educator

Hi there.

There are some concerns regarding this experiment.

1. The chemical equation you have written is correct. You can further form carbonic acid from H2O and CO2. Take a look at this:

Na2CO3 + 2HCl ---> 2NaCl + H2O +CO2 eq1

H2O + CO2 ---> H2CO3 (carbonic acid) eq2

-------------------------------------------------

Na2CO3 + 2HCl ---> 2NaCl + H2CO3 eq 3

You can use the equation 3 to solve for the concentration of carbonic acid.

2. The calculation for the number of moles of Na2CO3 is correct. We have concerns for the concentration of HCl. Please specify the concentration of the HCl reagent that you used. You cannot simply assume 50ml = 50 grams. Remember that you used a solution of HCL meaning that 50 mL HCl solution has concentration. Please ask your instructor what is the concentration of HCL that has been used in the experiment.

If you have the concentration already, let say it is in molarity, you can just get the number of moles by multiplication.

moles HCl = (concentration of HCL reagent) x (50 mL)

Now from here you can proceed in selecting the limiting reagent.

3. Solving for the concentration of the carbonic acid can be accomplished using the formula:

moles carbonic acid/ L solution

Moles of carbonic acid can be solve using stoichiometry. Just be sure item 2 is solved. The total volume of the solution is needed as well.

hope this helps :)

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