# Chemical Forums

## Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Aufbau89 on January 21, 2007, 08:36:26 PM

Title: Solution & molality questions
Post by: Aufbau89 on January 21, 2007, 08:36:26 PM
Concentrated sulfuric acid (18.4-molar H2SO4) has a density of 1.84 grams per milliliter.  After dillution with water to 5.20-molar, the substance has a density of 1.38 grams per millilter and can be used as an electrolyte in lead storage batteries for automobiles.

a) Calculate the volume of concentrated acid required to prepare 1.00 L of 5.20-molar  H2SO4.
b) Determine the mass percent of  H2SO4 in the original concentrated solution.
c) Calculate the volume of 5.20-molar  H2SO4 that can be completely reacted with 10.5 grams of sodium bicarbonate, NaHCO3, in the reaction: 2NaHCO3 +  H2SO4 -->  2H20  + NasSO4 + 2 CO2
d) What is the molality of the 5.20-molar  H2SO4?

Work

a) (5.20M)(1.00L)= moles  H2SO4
= 5.20 moles  H2SO4

(5.20 moles)/(18.4M) = 0.28L  ?

-I'm sorry, this is a confusing chapter for me.  Can someone help me out with b,c, and d?  And was my A correct?  Sorry.  I really need help.
Title: Re: Solution & molality questions
Post by: Borek on January 22, 2007, 03:50:08 AM
a. OK

b. Check http://www.chembuddy.com/?left=concentration&right=percentage-to-molarity - this is other way around, but you can easily solve final formula for C%.

c. Simple stoichiometry. Start calculating number of moles of substance in 10.5 g of sodium bicarbonate.

d. This one is a little bit more tricky. Look at the definition of molality (http://www.chembuddy.com/?left=concentration&right=molality) - assuming you have 1L of solution, how can you calculate number of moles of acid and mass of solvent?
Title: Re: Solution & molality questions
Post by: Aufbau89 on January 28, 2007, 03:45:18 AM
Ok thanks, I got it now.   ;D