Empirical and Molecular Formula

Q. Given that the abundance of isotopes 54Fe, 56Fe and 57Fe is 5%, 90% and 5%, respectively. The atomic mass of Fe is

1. 55.25 u
2. 55.95 u
3. 55.75 u
4. 56.95 u

Q.

How do you find the molecular formula of a compound?

Q. Two oxides of a metal contain 27.6%and30.0% of oxygen, respectively. If the formula of the first be M3O4. Then that of the second is .

1. $M_3$$O_5$
2. $M_2$$O_3$
3. $M_3$$O_3$
4. $M_3$O${}_2$

Q. A certain alkaloid has 70.8% C, 6.2% H and 4.1% N and rest O. The empirical formula of the alkaloid is

1. $C_{20}{H}_{21}N{O}_4$
2. $C_{20}{H}_{20}N{O}_4$
3. $C_{21}{H}_{20}N{O}_3$
4. $C_{20}{H}_{10}N{O}_3$

Q. A compound on analysis gave the following percentage composition.

Na—14.31 %	S—9.97 %
H—6.22 %	O—69.5 %.

Calculate the molecular formula of the compound, if all the hydrogen present in the compound is combined with oxygen to form water of crystallization. Molecular mass of compound is 322.
[Na = 23, S = 32, H = 1, O = 16]

Q.

A gaseous hydrocarbon contains 82.76 % of carbon. Given that its vapour density is 29, find its molecular formula

Q. What is the empirical formula of kaolin the percentage composition is which is as under: Al2O3= 39.5percent , SiO2 = 46.6 percent, H2O= 13.9 percent

Q.

Naturally occurring Boron consists of two isotopes whose atomic weights are 10.01 and 11.01. The atomic weight of natural Boron is 10.81. Calculate the percentage of each isotope in natural boron.

Q.

The empirical formula of a compound is $\mathrm{CH}$. Its molecular weight is $78\mathrm{g}$. The molecular formula of a compound will be

1. ${\mathrm{C}}_2{\mathrm{H}}_2$

2. ${\mathrm{C}}_3{\mathrm{H}}_3$

3. ${\mathrm{C}}_6{\mathrm{H}}_6$

4. ${\mathrm{C}}_4{\mathrm{H}}_4$

Q.

The empirical formula of a compound is ${\text{CH}}_{\text{2}}\text{Cl}$. If the molecular mass of the compound is $99\text{g}$, what is the molecular formula of the compound?

Q.

A hydride of nitrogen contains 87.5 per cent by mass fo nitrogen. Determine the empirical formula of this compound.

Q.

An organisc compound, whose vapour density is 45, has the following percentage composition,
H = 2.22 % O = 71 . 19% and remaining carbon.

Calculate:
(a) its empirical formula, (b) its molecular formula.

Q.

A hydrocarbon contains 4.8 g of carbon per gram of hydrogen.
Calculate:
(a) the gram atom of each,
(b) find the empirical formula,
(c) find molecular formula, if its vapour density is 29.

Q.

Find the empirical formula of the compounds with the following percentage composition.
Pb = 62.5%; N = 8.5 %. O = 29.0%

Q.

Find the molecular formula fo a hydrocarbon having vapour density 15, which contains 20% of Hydrogen.

Q.

The empirical formula of a compound is ${\mathrm{CH}}_2\mathrm{O}$. Find the molecular formula of the compound if its molecular weight is $180$.

Q.

Calculate the formula mass of Sodium nitrate $\left({\mathrm{NaNO}}_3\right)$.

Given: Atomic masses of Na = 23u, N = 14u, 0 = 16u

Q.

A gaseous compound of nitrogen and hydrogen contains 12.5% hydrogen by mass.

Find the molecular formula of the compound if its relative molecular mass is 32. [N= 14, H=1],

1. N₂H₄

2. N₂H₃

3. N₃H₇

4. N₄H₂

Q.

On analysis, a substamnce was found to contain;
C = 54. 54% H= 9.09 % O = 36.36 %
The vapour density fo the substance is 44, calculate:
(a) its empirical formula, (b) its molecular formula.

Q.

Calculate the percentage of phosphorus in the fertilizer superphosphate, Ca(H₂PO₄)₂ (correct to 1 decimal place.) [Ca = 40, H = 1, P = 31, O = 16]

Q. What is the chemical formula of wood but in the lost in island video they show that chemical equation of wood is C6H12O6 but it is formula of glucose

Q.

(a) Calculate the percentage of boron (B) in borax (Na₂B₄O₇·10H₂O). (H = 1, B = 11, O = 16, Na = 23).
(b) (i) The compound A has the following percentage composition by mass:
Carbon = 26.7%, oxygen = 71.1%, hydrogen = 2.2%. Determine the empirical formula of A (H = 1, C = 12, O = 16)
(ii) If the relative molecular mass of A is 90, what is the molecular formula of A?

Q.

A compound contains 87.5% by mass of nitrogen and 12.5% by mass of hydrogen. Determine the empirical formula of this compound.

Q.

How many moles of H2SO4 contains 4 grams of sulphur in it?

Q.

If the empirical formula of two compounds is CH and their vapour densities are 13 and 39 respectively, find their molecular formula.

Q.

A compound has O = 61. 32 % S = 11.15 % H = 4.88 % and Zn = 22.65 % The relative molecular mass fo the compound is 287 a.m.u. Find hte molecular formula of the compound assuming that all the hydrogen is present as water of crystallisation.

Q.

In an organic compound, the percentage of carbon and hydrogen are 40 and 6.7, respectively. If the vapor density of compound is 30, what is the molecular formula of the compound.

Q.

The percentage composition of sodium phosphate as determined by analysis is 42.1% sodium, 18.9% phosphorus and 39% oxygen.

Find the empirical formula of the compound (work to up to two decimal places). [Na = 23, P = 31, O = 16]

1. Na₃PO₄

2. Na₂PO₄

3. Na₂PO₃

4. Na₃PO₂

5. Na₆PO₃

Q.

An acid of phosphorus has the following percentage composition phosphorus = 38.27% hydrogen = 2.47% oxygen = 59.26 . Find the empirical formula of the acid and its molecular formula, given that its relative molecular mass is 162.

Q. The concentration of 9.8 g of H2SO4 in 500 ml solution is ?

(A) 0.5 M (B) 0.2 M (C) 0.4 N (D) 0.02 M

please tell me the formula to find it also?