[bcabanayan]

We've been assigned a lab in which we have to determine the percentages by mass of two solids in a mixture. The two solids in the mixture are sodium chloride and sodium bicarbonate. Available to us are common laboratory equipment, as well as 1 M hydrochloric acid and 1 M sulfuric acid. In addition, we also have the pure solids themselves.

I've tried to do some chemical equations (specifically, taking each solid in the mixture and then reacting them with either HCl or H2SO4), but I'm still relatively clueless as to how to isolate each component within the mixture.

Also, is bicarbonate similar to carbonate in that it reacts with an acid to produce carbon dioxide, water, and a salt?

Thanks for any help you can give me.

[Alberto_Kravina]

Well, after having set up an equation you can realize that sodium chloride does not react with HCl. It reacts only with bicarbonate (set up an equation for this reaction as well). Assuming that you have only NaCl and NaHCO₃ in your mixture you can just calculate w(NaHCO₃).
NaCl is the rest.

[bcabanayan]

So, my equation is...

2NaHCO₃ + H₂SO₄ -> Na₂SO₄ + 2H₂CO₃ ?

Also, I'm not totally sure what by what you mean by "w(NaHCO₃)."

Thank you!

[Alberto_Kravina]

2NaHCO3 + H2SO4 -> Na2SO4 + 2H2CO3 ?

Correct - although carbonic acid (H₂CO₃) decomposes in carbon dioxide and water.

Also, I'm not totally sure what by what you mean by "w(NaHCO3)."

w = percentages by mass  so  w(NaHCO₃) = percenage by mass of sodium bicarbonate

[bcabanayan]

Well, if I dissolved the mixture in HCl, wouldn't I still have Na₂SO₄ with the NaCl in the water (I'm assuming that the CO₂ evaporates as a gas...)? How would I separate the NaCl from the Na₂SO₄?

[Yggdrasil]

The purpose here is not to separate the two component, but to titrate a solution of your mixture with HCl to determine the amount of sodium bicarbonate in your mixture.  From the amount of HCl which reacts with your compound, you can figure out the amount of sodium bicarbonate in your mixture.

For example, lets say you disolve 2g of your mixture in water, and titrate.  From the titration, you find that there were 1.5g of sodium bicarbonate in your solution.  This means that your mixture contains 1.5g of sodium bicarbonate and 0.5g NaCl per 2g, or a 1:3 ratio of NaCl:sodium bicarbonate.

[Borek]

Either titration or gravimetry - weight sample, add excess HCl, dry, weight solid. Mass difference gives information about bicarbonate present.

[bcabanayan]

In regards to the titration...

How would I titrate without knowing the concentration of the NaCl/NaHCO₃ in the water? Also, what type of indicator would I use?

Either titration or gravimetry - weight sample, add excess HCl, dry, weight solid. Mass difference gives information about bicarbonate present.

Exactly what type of information does the mass difference give?

[Borek]

How would I titrate without knowing the concentration of the NaCl/NaHCO₃ in the water?

You titrate to determine this concentration, you don't know it beforehand. You may estimate maximum concentration value assuming your sample (of known mass) is pure bicarbonate.

Also, what type of indicator would I use?

Any universal bicolor, like methyl orange, will do. See http://www.ph-meter.info/pH-measurements-indicators.

Either titration or gravimetry - weight sample, add excess HCl, dry, weight solid. Mass difference gives information about bicarbonate present.

Exactly what type of information does the mass difference give?

This example of stoichiometric calculation should give you a hint:
http://www.chembuddy.com/?left=balancing-stoichiometry-questions&right=stoichiometry-q8

[bcabanayan]

How would I titrate without knowing the concentration of the NaCl/NaHCO₃ in the water?

You titrate to determine this concentration, you don't know it beforehand. You may estimate maximum concentration value assuming your sample (of known mass) is pure bicarbonate.

Oh, duh...

So, if the sample contains sodium chloride and sodium bicarbonate, I can't use titration? I'm slightly confused. Sorry...

[Borek]

Titrating with HCl (or H₂SO₄) you can determine amount of bicarbonate, as NaCl will not react with the acid. See http://www.titrations.info/ for the very brief information.

[bcabanayan]

Would you be able to determine the amount of bicarbonate or sodium bicarbonate?

Sorry about all the questions.  We haven't really discussed titration since Honors Chemistry last year. 

[Borek]

Would you be able to determine the amount of bicarbonate or sodium bicarbonate?

Try to write reaction equations and think for youself. You may determine amount of bicarbonate in moles. Does it matter what kind of bicarbonate it is?

[chiralic]

Hi...

In this book:
L. F. Hamilton, S. G. Simpson, Calculations of Analytical Chemistry, you'll find in details
how to determinate NaHCO3 + NaCl....(also find a lot exercises, graphics, how to calculate...)

Regards,
Chiralic