I only need the answers (lol).. I got these questions wrong, but I want to see w
ID: 834299 • Letter: I
Question
I only need the answers (lol).. I got these questions wrong, but I want to see where I can find my own mistake.
1. Calculate the atomic weight of platinum if 0.8930 mol of the metal has a mass of 174.2 grams?
2. What is the empirical formula of the compound formed when 8.82 grams of copper metal react with excess chlorine to give 13.74 grams of the compound?
3. ?-Carotene is the protovitamin from which nature builds vitamin A. It is widely distributed in the plant and animal kingdoms, always occurring in plants together with chlorophyll. Calculate the molecular formula for ?-carotene if the compound is 89.49% C and 10.51% H by mass and its molecular weight is 536.89 grams/mol.
4. Caffeine is a central nervous system stimulant found in coffee, tea, and cola nuts. Calculate the molecular formula of caffeine if the compound is 49.48% C, 5.19% H, 28.85% N, and 16.48% O by mass and has a molecular weight of 194.2 grams per mole.
Explanation / Answer
1) atomic weight = mass/moles = 174.2/0.893 = 195.07 gm/mol
2) Cu(s) + excess Cl2 ---> CuCln
Cu moles = 8.82/63.546 = 0.1388
since Cl2 is excess CuCln moles = Cu moles = 0.1388
given mass of CuCln = 13.74 gm
mol mass of CuCln = 13.74/0.1388 = 99 gm/mol
Cu mol mass + nCl mol mass = 99
63.5 + n(35.5) = 99
n = 1 hence emperical formula is CuCl
3) we now divide by respective atomic weigts to get ratio C = 89.49/12 = 7.4575 , H = 10.51/1 = 10.51
we now divide both by small number 7.4575 , C =7.4575/7.4575 = 1 , H = 10.51/7.4575 = 1.4
hence 1.4 H per 1C which means C10H14 is emperical formula
hence emperical formula is (C10H14)n
mol mass = 536.89 gm/mol hence (10 x 12 + 14 ) n = 536.89
n = 4 , hence formula is (C10H14) x 4 = C40 H54
4) C = 49.48/12 = 4.123 , H = 5.19 , N = 28.85/14 = 2.06 , O = 16.49/16 = 1.03
now dividing whole by 1.03 , C = 4.123/1.03 = 4 , H = 5.19/1.03 = 5 , N = 2 , O = 1
emperical formula is C4H5N2O
its mol mass is 4x12 + 5 + 28 + 16 = 97 gm /mol
nowe 97 x n = 194.2 , n = 2
hence mol formula is (C4H5N2O)2 = C8H10N4O2