if you use the concentrated HNO3 which is 65%, so you can use this equation :

C1V1 = C2V2

65*V1 = 2*100

V1 = 200/65

V1 = 3.07 ml

so dilute 3.07 mL concentrated HNO3 with 96.93 mL H2O

Thank you

i) We should generally take not fully specified % concentrations as wt% ― where wt is often omitted or can be substituted by either wt., wt/wt, wt./wt., or m/m ― meaning: (mass of pure solute / mass of solution)·100%; even if this is not clearly stated. If is required to prepare the requested solution to exactly fullfil a given volume, the density of the solution for that same concentration, at a given temperature, should be known. Concentrations are typically given in a solute to solution basis; not in a solute to solvent basis. A rare exception is molality (mol solute / kg solvent).

ii) I shall suppose that you intend to dilute commercial conc. HNO3 65.0 wt% aq. sol., to obtain dilute HNO3 2.00 wt% aq. sol.

iii) The concentration of conc. HNO3 aq. is 0.650 (g HNO3/ g solution)·100%. The density of that conc. acid is 1.391 g/cm3 (20 ºC) after (e.g.) Table 2-66 in: R.H. Perry, D.W. Green, J.O. Maloney (Eds.), "Perry's Chemical Engineers’ Handbook", 7th ed., McGraw-Hill, 1997. The density is usually also available from the commercial label. The molecular mass of HNO3 is 63.012 g·mol−1. The molarity (equals normality) is: 0.650(g HNO3 / g aq. sol.)·1.391(g aq. sol. / cm3)·(1000 cm3/dm3)/(63.012 g HNO3/mol HNO3) = 14.35 M (approximate).

iv) The concentration of dilute HNO3 aq. is 0.0200 (g HNO3/ g solution)·100%. The density of that dilute acid is 1.009 g/cm3 (20 ºC) (ibidem). The molarity is: 0.0200(g HNO3 / g aq. sol.)·1.009(g aq. sol. / cm3)·(1000 cm3/dm3)/(63.012 g HNO3/mol HNO3) = 0.320 M.

v) The intended dilute solution can be then volumetrically prepared, at approx. 20ºC, while considering the appropriate (volumetric) dilution factor:

Vfinal/Vinitial = (14.35 M)/(0.320 M).

vi) Alternatively, but in principle less conveniently, the dilute solution could be prepared gravimetrically by considering the following.

Mass balance for the solute (HNO3) on the dilution operation:

{65.0 wt% (solute:solution)}·minitial solution =

{2.00 wt% (solute:solution)}·mfinal solution

Mass balance for the solution on the dilution operation:

minitial solution + madded Water = mfinal solution

where:

madded Water (g) could be readily converted to Vadded water (cm3) by considering the water density (0.998 g/cm3 at 20 °C).

minitial solution can be readily converted to Vinitial solution (cm3) based on its density if available from the commercial label.

This procedure allows the dilute solution to be prepared without reference to the acid density table.