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Postby Jaime_Chamberlain_3G » Thu Oct 06, 2016 10:12 pm

Could someone please help explain how to start off G5 from the review? The question is: A student prepared a solution of sodium carbonate by adding 2.111g of the solid to a 250.0 ml volumetric flask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student transfer into a flask to obtain (a) 2.15 mmol Na+; (b) 4.98 mmol Co3^-2; (c) 50.0mg Na2CO3? I already figured out the molarity, but I'm not sure what to do next.

Sydmon Nguyen-Tran 1N
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Re: G5

Postby Sydmon Nguyen-Tran 1N » Thu Oct 06, 2016 10:49 pm

So you're trying to find the volume and you have the moles for Na (for part a) and the molarity. Using stoichiometry, start with 2.15mmol Na divided by the molarity you found (.07967M) and then multiply that by the ratio of moles of Na2CO2 (1 mol) to Na (2 mol), giving you 13.5mL. You repeat this formula for part b, but replace the givens and mole ratio.

Ashley T 2H
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Postby Ashley T 2H » Thu Oct 06, 2016 11:41 pm

Also, for part C, convert the 50.0 milligrams of sodium bicarbonate to grams and multiply it by the 250.0mL volume/2.111gram solid originally given. This will give the volume (in mL) of solution you want to transfer into the flask.

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