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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Help a guy out on September 27, 2020, 05:29:23 PM

Title: Chem Hw Help Its been 3 years and man i do not remember at all!!
Post by: Help a guy out on September 27, 2020, 05:29:23 PM

A certain brine has 3.82% NaCl by mass. A 75.0−mL sample weighs 76.7 g
How many liters of this solution should be evaporated to dryness to obtain 730 kg NaCl?

I have been trying to use M1v1 = m2v2 But I have to use the mass percent that is given to me and mole fraction I think. I not sure if I am to convert the massese given to me as moles using the density also or just use the mass given to me? I am over thinking this WAY TOO MUCH Help me dear god! and thank you for time!

Title: Re: Chem Hw Help Its been 3 years and man i do not remember at all!!
Post by: Borek on September 27, 2020, 06:39:23 PM

No need for molarities here.

What is the mass of the NaCl in the 75 mL sample of the solution?

How many such samples needed for 750 kg of NaCl?


Alternatively, if thinking in terms of 75 mL samples throws you off - what is the density of the solution? What is mass of 1L? How many grams of NaCl from drying out 1L?

Title: Re: Chem Hw Help Its been 3 years and man i do not remember at all!!
Post by: Help a guy out on September 27, 2020, 06:59:24 PM

Would I get the denseity then divide it by a 1000 grams to cancel grams then mulitpy it by 750kg?

Title: Re: Chem Hw Help Its been 3 years and man i do not remember at all!!
Post by: Borek on September 28, 2020, 03:20:41 AM

No you are just guessing. It never works.

I suggested step by step conversion - do you remember factor label method?