What Is the Molarity of Concentrated Nitric Acid?

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Discussion Overview

The discussion revolves around calculating the molarity of concentrated nitric acid, which is specified as 70.7% HNO3 by mass. Participants explore the relationship between mass, volume, and moles, while addressing the density of the solution and the implications for molarity. The context includes a homework problem requiring the application of chemical principles.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents a homework problem involving the calculation of molarity for concentrated nitric acid, providing the mass percentages and density of the solution.
  • Another participant suggests using specific mass amounts (70.7g of HNO3 and 29.3g of H2O) to simplify calculations.
  • A participant calculates the number of moles of HNO3 and H2O based on the provided mass percentages but questions the relevance of multiplying by 2.
  • There is a clarification regarding the density unit, with one participant confirming it as g/cm³.
  • A participant incorrectly suggests multiplying the mass of HNO3 by the number of moles to find mass, which is corrected by another participant who emphasizes using the total mass of the solution to find volume.
  • One participant successfully calculates the volume of the solution using the density and total mass, leading to a molarity calculation.
  • Another participant encourages the original poster to check the units used in their calculations, particularly for volume and molarity.

Areas of Agreement / Disagreement

Participants generally agree on the approach to calculating molarity, but there are moments of confusion regarding the application of formulas and units, indicating that the discussion is not fully resolved.

Contextual Notes

Participants express uncertainty about the correct application of formulas and the significance of units in calculations, which may affect the final results.

Who May Find This Useful

This discussion may be useful for students working on chemistry problems involving molarity, density, and mass percentages, particularly in the context of solutions and concentrations.

geffman1
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Homework Statement


hey guys, i got a problem. "concentated nitric acid is 70.7% HNO3 (molar mass=63g) and 29.3% H20 by mass. the density of the solution is 1.42gcm. what is the molarity.


Homework Equations


i know i should rearrange the formula d=m/v but i can't work out the mass because how do i know how many moles of HNO3 do i have? i tried writing empricial formula but I am a bit lost. any help would be greatlyfull apprecitated.


The Attempt at a Solution


P.s I've got an assesment and i have a few worked questions, if anyone would like to check one or 2 answers please let me know. thanks
 
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Start by working with those mass-% numbers. You may assume any amount of HNO3 and H2O, as long as they are in the right proportion. So to make life simple, use 70.7g of HNO3 and 29.3g of H2O.
 
yeh i did that but when i worked it out i get 1.122 moles of HNO3 and 1.623 moles of H20. should i just mulitiple both by 2?
 
Not sure what good multiplying by 2 does.

At any rate, you now have how many moles of HN03. Given the density 1.42gcm (is that 1.42 g/cm3?), you can figure out the volume of the solution.
 
so if i times 70.7 grams by 1.122 that should give me the mass of HNO3
 
oh soz, yeh it is cm^3
 
Uh, no, the mass of HNO3 is 70.7 grams. 70.7g x 1.122mol would be meaningless here.

The total mass of the solution is 100.0 grams. Use the density to get the volume of the solution.
 
o true. so it would work out v=m/d =100/1.42=70.422. then molarity would equal moles/volume which would equal 1.122/70.422=0.0159
 
thansk mate your a ledgend.
 
  • #10
You are very very close, hang in there.

Watch those volume units:
What are the units for the v=70.4 you calculated?
What volume units are used to calculate molarity?
 

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