Question

1- Calculate the following: A- Number of moles in 10 gram of Cr(NO3)s. B Number of Atoms in 2.5 gram of Cr(NO3)s C- Number of molecules in 100 gram of Fe(NO3)s. D- Number of grams in 10 20 atoms of Fe(NO3)s. 2- Complete the following table: Element С н % Composition 71 Empirical Formula Element Н % Composition 65.4 5.5 29.1 Empirical Formula 29

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Answer 1

This question is solved as follows:

Sol: 1(A) Number of moles in 10 gram of aber of moles in 10 gram of Ca(NO3)5 - more We have to calculate no. of moles ie; egon weight of comp - molecular weight of comp. no of moles & Co (51.996+ (14 +16X3)5) 51.996+ 3 10 to 361.996 0.027625 Ang no. of moles = (of Cr KNO3);) atomic mass of almol r = 51.996 u or N = 14 ur 0 = 16 u . " " (B) Number of atoms in 2.5 gms. of Cr (NO3)5 = ? Let us calculate no. of moles first of all - no. of moles - Im Col. of Cr (NO) molecular col of Ca(NO3)5

n = 2 2.5 (519967 074 + 16X35) 2.5 (51.996 + 310) 2.5 367996 - =0.006906 atoms in 1 mole of a comp. = 6.0 n = no. of Semila of atoms in of atoms in no. I mole of C (NO3) = 6.02 x 1025 0.00690 mole of Cr (NO3)5 = 6:02 x 1023x8.00 6906 = 0.04 157 x 1023 or 4.15 7 x 1025 na atoms Aus ne atoms (C) No. of molecules in 100 grams of Fe(NO3)3. no. of moles in 100 grams of fe (NO3)3 = mo NO3)3 molecular cot offe (NO) 100 (55.847 + (14 + 16X3)3) loo (55.847 +14+ 48)3) Ce = 55.8474 IN- 14 u to=16u 1oo 55.847 + 186 Joo 241.847 = 0. 413 48 = 0.4135 n now, '" no. of molecules in " " Imole Fe(NO3)3 = 6.02 x 1023 0.4155mole Fe(NO3) = 6:02 x 102 x 0.4135 = 2.489 x 1023.. I molecules

1. Number umber of grams in 102 atoms of Fe(NO3)3. 6.02 x 1023 atoms are present in = 1 - I atom is " = 5.02 x 1023 1020 atoms are . 1 mole h 6.02 x 1023 1020 6.02 X 1023 6.02 = 0.166 x 10-3 or 1.66 x 10 mote Therefore 10 20 atoms ar atoms are present en 1.66x 10-t mole of fe (NO3). no of moles of fe (NO) is gm col of fe (NO3)2 molecular cot of fe (NO3); 1.66 x 10-4 gricot of fe (NO3)3 (241.847) gm. aut. of Fe(NO3)3 = 1.66 x 10-+ x 241.847 401.466 x 10-4 = 4.0 1466 x 10-2 gm. i Number of grams in 1020 atoms of Fe(NO3)3 es 4.0 14 66 x 10 gm A