Percent composition. Please help meee :(

Explanation:

Formula of percent composition:

% X = ( mass of element in compound / total mass of compound ) × 100

11) Al₂O₃

Al = 27 g/mol

O = 16 g/mol

%Al = (54 / 101.96) × 100

%Al = 52.9%

%O = (48 / 101.96) × 100

%O = 47.1%

12) C₅H₅O₅

C = 12 g/mol

H = 1 g/mol

O = 16 g/mol

C% = (60 / 145 ) × 100

C% =41.4%

H% = (5 / 145 ) × 100

H% =3.4%

O% = (80 / 145 ) × 100

O% = 55.2%

13) BaBr₂

Ba = 137.3 g/mol

Br =79.9 g/mol

Ba% = (137.3 / 297.14) × 100

Ba% = 46.2%

Br% = (159.8/ 297.14) × 100

Br% = 53.8%

14) Fe₃(PO₃)₂

Fe = 55.8 g/mol

P = 31 g/mol

O = 16 g/mol

Fe = (167.4/325.48)  × 100

Fe = 51.43%

P = (62/325.48)  × 100

P = 19.05%

O = (96 /325.48)  × 100

O = 29.49%

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number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.