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AS Chemistry planning excercise - any hints? Kinda urgent...

"Baking powder contains sodium hydrogencarbonate, NaHCO3.

Describe a procedure that does NOT involve a titration, by which you can determine the % by mass of sodium hydrogencarbonate in baking powder.

Your procedure must make use of the reaction of NaHCO3 with sulphuric acid".


I'm the only guy in the class retaking this, so I'm having to come up with this all by myself.


The idea I had was to neutralise a certain volume of H2SO4(aq) with the NaHCO3(s) - I'd know when this happens because it'd stop giving off CO2 (carbonate + acid = salt + water + CO2) and from the balanced equation I'd be able to work out the mass needed, and therefore %age composition, pretty easily.


But... There's acid in the baking soda... That's how it works, you get it wet, the NaHCO3 reacts with the acid, you get a neutral salt and CO2 that rises the dough. It doesn't say what this acid is. That's what I'm worried about... Is my method OK, or would the acid in the baking soda interfere with the reaction I described above? This has to be in by Friday :s
Reply 1
u have to use sulphuric acid...hw much acid u gna use and hw much of the baking soda r u gna use in ur experiment
Well, I worked out if you had, say, 100ml of 1mol/dm3 sulphuric acid solution, you'd need about 25g NaHCO3 to neutralise it, but since I don't know the percentage NaHCO3 makes of the total baking powder mass, I could need anything up to 100g of it?


It's not really important, I just need to describe the experiment. But if I add the baking powder directly to the H2SO4, surely the acid in the baking powder's gonna neutralise some of the NaHCO3 in the baking powder? How do I get round that?
Reply 3
look forget about the neutralising stuff...u add the baking powder to the sulphuric acid... 2NaHCO₃+ H₂SO₄ ------>Na₂SO₄ + 2H₂O + 2CO₂.....so u get CO2 gas given off. which comes from the NaHCO3...so u measure hw much off that u get in da measurin cylinder...n den u work from der
Okay. But the baking powder contains an acid, so when I put the baking powder into the sulphuric acid solution, wouldn't it dissolve and combine with the NaHCO3 and give off its own CO2? Wouldn't that be a major source of error?
Reply 5
ok noo the baking powder doesnt have an acid....if it did then it wud have reacted wit the NaHCO3 already....just look u dnt need to kno wat else is in the baking powder...dey r jus impurities....u just concerned about the NaHCO3and the CO2 since the CO2 came from the NaHCO3...i just dnt kno hw to do the calculations...da method n da rest of the stuff is easy
But baking powder consists of the NaHCO3 along with an acid, so when it gets wet, the base and the acid dissolve and react... That's how baking powder works, and that's what's giving me a headache :biggrin:
Reply 7
but the other acid doesnt contain Carbon.....so any carbon present must have come from NaHCO3
Good point. Cheers for the assistance fella :smile:

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