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### Topic: Quick question  (Read 2557 times)

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#### zeshkani_usa

• Regular Member
•   • Posts: 13
• Mole Snacks: +0/-1 ##### Quick question
« on: January 16, 2013, 09:03:24 PM »
Hi there,

I have 1 question I have done it just wondering some feed back if this is right.

1.Calculate the Density of NaCl at 20C in [lbm/ft3]

here i used the Specific gravity of NaCl and which was 135lbm/ft3 multiply by 62.43lbm/ft3 which is the ref. for most soilds and liquids but this gives a very large density of 8370 lbm/ft3
but i was wondering if this could be done by using the V=nRT/P plug V into the D=M/V => D=m/(RT)
since there is no mention of the weight of NaCl i assumed 1mole
by doing this i get this answer 1.497022809933 lb/ft3 to get lbm/ft3 i just divied 1.49/32.2 =0.0357lbm/ft3
why is there such a difference between these 2 answers
is there a better method of doing this?

#### sjb

• Global Moderator
• Sr. Member
•   • Posts: 3640
• Mole Snacks: +220/-42
• Gender:  ##### Re: Quick question
« Reply #1 on: January 17, 2013, 02:37:33 AM »
Hi there,

I have 1 question I have done it just wondering some feed back if this is right.

1.Calculate the Density of NaCl at 20C in lbm/ft3

here i used the Specific gravity of NaCl and which was 135lbm/ft3 multiply by 62.43lbm/ft3 which is the ref. for most soilds and liquids but this gives a very large density of 8370 lbm/ft3
but i was wondering if this could be done by using the V=nRT/P plug V into the D=M/V => D=m/(RT)
since there is no mention of the weight of NaCl i assumed 1mole
by doing this i get this answer 1.497022809933 lb/ft3 to get lbm/ft3 i just divied 1.49/32.2 =0.0357lbm/ft3
why is there such a difference between these 2 answers
is there a better method of doing this?

What is the full name of the unit you are using? lbm/ft3? Check your units, what is the name of the formula you are using in the V=nRT/P strp?