Question

write the chemical formulas, calculate the molecular masses and find the percent of oxygen in the following compounds:

a.) compound containing sodium and phosphate:

b.) Compound containing calcium and sulfate

c.) Compound containing Ammonium and carbonate:

d.) Compound containing barium and hydroxide:

2.) Calculate the number of molecules in 4.5 moles of Ca(ClO3)2.

3.) Calculate the mass of (NH4)2CO3 in 4.0 moles of (NH4)2CO3.

4.) Calculate the number of molecules in 7.3 g of calcium sulfate.

5) Calculate the empirical formula of each compound from the percent compositions.

a.) 25.9% N, 74.1%O

b) 3.99% P, 82.3%Br, 13.7%Cl

6.) Butyric acid is compound that is present in butter. It has a molar mass of 88.11g/mol and is composed 54.5% C, 9.2%H, and 36.3% O. what is the molecular formula of butyric acid.

Answer 1

(a) Sodium(Na) has +1 charge.

Phosphate(PO₄^-3) has -3 charge

upon combining the compound formed is Na₃PO₄

Molecular mass of Na =23 amu

Molecular mass of P =31 amu

Molecular mass of O =16 amu

Molecular mass= (3*23)+(31)+(4*16)=164 amu

Mass of oxygen (per molecule)=(4*16)=64 amu

Mass % of oxygen={(Mass of oxygen)/(Molar mass of compound)}*100

= (64/164)*100 =39.02 %

Thus mass% of oxygen is 39.02%

(b) Calcium(Ca) has +2 charge

and sulfate (SO₄^-2) has -2 charge.

Compound formed= CaSO₄

Molecular mass of 'Ca' and 'S' are 40 amu & 32 amu respectively.

Molecular mass of CaSO₄ =(40)+(32)+(16*4) =126 amu

Mass of oxygen=16*4 =64 amu

Mass% of oxygen =(64/126)*100 = 50.79%

(c) Ammonium = NH₄⁺   : Charge=+1

carbonate= CO₃^2- : charge=-2

Compound formed= (NH₄)₂CO₃

Molecular mass of 'N' ,'H' & 'C' are 14 amu, 1amu & 12 amu respectively

Molecular mass of (NH₄)₂CO₃ = 2*(14+4) + 12+ (3*16) = 98 amu

Mass of oxygen=48 amu

Mass % of oxygen =(48/98)*100 = 48.98%

(d)Barium : Ba = charge =+2

hydroxide: OH   charge =-1

Compound formed: Ba(OH)₂

Molecular mass of 'Ba' is 137 amu

Molecular mass of = 137+(16+1)*2 =171 amu

Mass of oxygen =16*2 = 32 amu

Mass % of oxygen = (32/171)*100 = 18.71%