[chm151]

hi , i have 2 chemistry questions:
 1) ethyl alcohol has a density of 0.789g/cm^3.  What volume of ethyl alcohol must be poured into a graduated cylinder to give 19.8 g. of alcohol?
 2) how many grams of sodium dichromate, Na_2Cr_2O_7, should be added to a 50.0 mL volumetric flaskto prepare 0.025 M sodium dichromate when the flask is filled to the mark with water? What are the molarities of the Na+ ion and the Cr_2O_7^2- ion in the solution?
    thanks a lot   

[Padfoot]

ethyl alcohol has a density of 0.789g/cm^3. 

OK, if there's 0.789g every cubic cm, then how many are needed for 19.8g.  Think division.

2) how many grams of sodium dichromate, Na_2Cr_2O_7, should be added to a 50.0 mL volumetric flaskto prepare 0.025 M sodium dichromate when the flask is filled to the mark with water? What are the molarities of the Na+ ion and the Cr_2O_7^2- ion in the solution?

Post what you've got so far 

[chm151]

i haven't started on this question yet, but i dont know where to start

[Padfoot]

2) how many grams of sodium dichromate, Na_2Cr_2O_7, should be added to a 50.0 mL volumetric flaskto prepare 0.025 M sodium dichromate when the flask is filled to the mark with water? What are the molarities of the Na+ ion and the Cr_2O_7^2- ion in the solution?

Well first calculate how many moles of sodium dichromate are in 50mL (0.05L) of the 0.025mol/L solution.  The first answer will simply be the mass of this (use molar mass).

For the second question, hint: you have use the coefficents of the dissociation rxn.