a. Calculate the mass of H3PO4 needed to make 100 ml of a 3M solution. Be sure to use the proper units in your answer.
b. Calculate the volume of the 3M solution of H3PO4 from part a. that would be needed to make a diluted solution of H3PO4 that is 50 mL and has a concentration of 2M. Be sure to use the proper units in your answer (L or mL)

Question

a. Calculate the mass of H3PO4 needed to make 100 ml of a 3M solution. Be sure to use the proper units in your answer.
b. Calculate the volume of the 3M solution of H3PO4 from part a. that would be needed to make a diluted solution of H3PO4 that is 50 mL and has a concentration of 2M. Be sure to use the proper units in your answer (L or mL)

jfraser · Answer

part a is two steps:

use the volume and concentration of the acid solution you need to make to find the $moles$ of acid needed.

then use the molar mass of $H_3PO_4$ to find the $grams$ needed

anonymous · Answer

part a. is actually 29.4 grams, can anyone show me how to do part b?

welshfella · Answer

the molar mass of phosphoric acid is 98 so 50 ml of 2M acid  will contain 
2 * 98 / 20 = 9.8 grams of the acid

welshfella · Answer

you have a 100 mls of acid which contains 29.4 g of H3PO4
and we need 9.8 g

so we must take  volume of 9.8 *100     mls = 33.33 mls of this acid to make 
                                           -------
                                               29.4
to make the 50 mls of 2M acid.

anonymous · Answer

thank you :) !!