22.37 g of chromium(II) nitrate, must be dissolved to prepare 500. mL of a 0.188 M aqueous solution of the salt.
According to the definition, the molar concentration of a substance in a solution is the ratio of the number of the moles to the volume of the solution:
c=n/V.
The number of the moles is related to the mass with the molar mass:
n=m/M;
m=n·M.
Thus, given the volume of the solution of chromium(II) nitrate, its concentration and molar mass is 238.011 g/mol we can calculate the mass of chromium(II) nitrate needed for the preparation :
∴ Cr(NO₃)₃ = cVM
= 0.188 M × 0.5 L × 238.011 g/mol
= 22.37 g
Therefore, 22.37 g of chromium(II) nitrate, must be dissolved to prepare 500. mL of a 0.188 M aqueous solution of the salt.
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