In Chemistry, #V_f and V_i# mean final volume and initial volume, and have to do with the dilution of solutions, where #M_iV_i = M_fV_f#. #M_i# = initial concentration in moles/L, and #M_f# = the final concentration in moles/L. If you know three of the four variables, you can calculate the unknown.
Example: What is the concentration of a solution prepared by diluting 25.0 mL of 6.00 M HCl to a total volume of 50.0 mL?
Given:
#V_i ="25.0 mL"#
#M_i = "6.00 M = 6 mol/L"#
#V_f = "50.0 mL"#
Unknown:
#M_f#
: Equation:
#M_iV_i = M_fV_f#
First we need to convert given volume to liters (because molarity is mol/L).
#V_i="25.0 mL x 1L/1000 mL= 0.0250 L"#
#V_f="50.0 mL x 1L/1000mL=0.0500 L"#
Solution:
#M_iV_i = M_fV_f#
Rearrange the variables and isolate #M_f#. Solve for #M_f#.
#M_f=(M_iV_i)/(V_f)="6.00 mol/L x 0.0250 L"/"0.0500L"="3.00 mol/L" = 3.00M#
