Empirical & Molecular Formula

Q.

An organic compound contains Carbon, Hydrogen and Oxygen. Its elemental analysis gave $\mathrm{C}$, $38.71\%$ and $\mathrm{H}$, $9.67\%$.The empirical formula of the compound would be?

1. $\mathrm{CHO}$

2. ${\mathrm{CH}}_2\mathrm{O}$

3. ${\mathrm{CH}}_3\mathrm{O}$

4. ${\mathrm{CH}}_4\mathrm{O}$

Q.

Determine the molecular formula of an oxide of iron in which the mass percent of iron and oxygen are 69•9 and 30•1 respectively

Q. A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g carbon dioxide, 0.690 g of water and no other products. A volume of 10.0 litre (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate molecular formula of gas.

1. None of the above
2. $C_2{H}_4$
3. $C_4{H}_8$
4. $C_2{H}_2$

Q.

The simplest formula of a compound containing $50\%$ of element X (atomic mass 10) and $50\%$ of element Y (atomic mass 20) is

1. $X_{2}Y$
2. $X{Y}_3$
3. $X_2{Y}_3$
4. $XY$

Q. Number of neutrons present in $1.7\text{g}$ of ammonia is:

1. $N_A$
2. $\frac{N_A}{10\times 4}$
3. $\left(N_A/10\right)\times 7$
4. $N_A\times 10\times 7$

Q. Butyric acid contains only $C,H$ and $O$. A 4.24 mg sample of butyric acid is completely burned. It gives 8.45 mg of carbon dioxide $\left(C{O}_2\right)$ and 3.46 mg of water. What is the mass percentage of each element in butyric acid?The molecular mass of butyric acid was determined by experiment to be88. What is the molecular formula?

1. Molecular formula = $C_4{H}_8{O}_2$
2. Mass percentage of $C$ = 44.35 %, $H$ = 19.06 %, $O$ = 36.59 %
3. Molecular formula = $C_3{H}_{8}O$
4. Mass percentage of $C$ = 54.35 %, $H$ = 9.06 %, $O$ = 36.59 %

Q. An organic compound contains 20% carbon, 6.7% hydrogen, and 46.67% nitrogen. Its molecular weight was found to be 60. Find the molecular formula of the compound.

1. $C{H}_{2}N{O}_2$
2. $C{H}_4{N}_{2}O$
3. $C{H}_2{N}_2{O}_2$
4. $C{H}_3{N}_{2}O$

Q.

The ratio of mass percent of $\mathrm{C}\mathrm{and}\mathrm{H}$ of an organic compound $\left({\mathrm{C}}_{\mathrm{X}}{\mathrm{H}}_{\mathrm{Y}}{\mathrm{O}}_{\mathrm{Z}}\right)\mathrm{is}6:1$. If one molecule of the above compound $\left({\mathrm{C}}_{\mathrm{X}}{\mathrm{H}}_{\mathrm{Y}}{\mathrm{O}}_{\mathrm{Z}}\right)$ contains half as much oxygen as required to burn one molecule of compound ${\mathrm{C}}_{\mathrm{X}}{\mathrm{H}}_{\mathrm{Y}}$ completely to ${\mathrm{CO}}_2\mathrm{and}{\mathrm{H}}_2\mathrm{O}$. The empirical formula of compound ${\mathrm{C}}_{\mathrm{X}}{\mathrm{H}}_{\mathrm{Y}}{\mathrm{O}}_{\mathrm{Z}}$ is

1. ${\mathrm{C}}_2{\mathrm{H}}_4\mathrm{O}$

2. ${\mathrm{C}}_3{\mathrm{H}}_4{\mathrm{O}}_2$

3. ${\mathrm{C}}_2{\mathrm{H}}_4{\mathrm{O}}_3$

4. ${\mathrm{C}}_3{\mathrm{H}}_6{\mathrm{O}}_3$

Q. Two elements $X$ and $Y$ have atomic mass $75$ and $16$ respectively. They combine to give a compound having $75.8\%$ $X$. The empirical formula of the compound is:

1. $X_2{Y}_2$
2. $XY$
3. $X_{2}Y$
4. $X_2{Y}_3$

Q. A compound contain 25% hydrogen and 75% carbon by mass. The empirical formula of the compound is:

1. $C{H}_4$
2. $C_2{H}_2$
3. $C_2{H}_6$
4. $C_2{H}_4$

Q.

What is the formula for finding the atomicity of an atom or element?

Q. An organic compound contains 40% of C, 6.66 % of H, 53.34 % of O. Predict it's molecular formula. The density of the compound at STP is 0.00535 g/mL.

1. $C_5{H}_{10}{O}_3$
2. $C_4{H}_8{O}_4$
3. $C_6{H}_{14}{O}_2$
4. $C_3{H}_2{O}_5$

Q. A given sample of pure compound contains $9.81\text{g}$ of $Zn$, $1.8\times {10}^{23}$ atoms of chromium and 0.60 mol of oxygen atoms. What is the simplest formula?

1. $ZnC{r}_2{O}_7$
2. $ZnC{r}_2{O}_4$
3. $ZnCr{O}_4$
4. $ZnC{r}_2{O}_6$

Q.

One litre of a gas at STP weight 1.16 g it can possible be

1. $CO$
2. $O_2$
3. $C{H}_4$
4. $C_2{H}_2$

Q.

Determine the empirical formula of an oxide of iron which has 69.9% iron and 30.1 % dioxygen by mass.

Q.

Calculate the formula unit mass of ZnO, Na2O and K2CO3. Give atomic mass of Zn = 65u Na = 23u K = 39u C = 12u O = 16u.

Q.

An oxide of sulphur contains 50% of sulphur in it. Its empirical formula is:

Q. At $300K$ and 1 atmospheric pressure, $10mL$ of a hydrocarbon required $55mL$ of $O_2$ for complete combustion and $40mL$ of $C{O}_2$ is formed. The formula of the hydrocarbon is:

1. $C_4{H}_8$
2. $C_4{H}_{7}Cl$
3. $C_4{H}_{10}$
4. $C_4{H}_6$

Q.

An organic compound contains 69.77% carbon, 11.63% hydrogen and rest oxygen. The molecular mass of the compound is 86. It does not reduce Tollen's reagent but forms an addition compound with sodium hydrogen sulphite and give positive iodoform test. On vigorous oxidation it gives ethanoic and propanoic acid. Write the possible sturcture of the compound.

Q.

Sodium carbonate (${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$) is an important industrial compound. Calculate its formula mass.

Q. Match the primitive unit cells given in Column I with their axial angles and axial distances given in Column II and select the correct answer from the codes given.

1. (i)-r, (ii)-s, (iii)-p, (iv)-q
2. (i)-r, (ii)-s, (iii)-q, (iv)-p
3. (i)-s, (ii)-r, (iii)-p, (iv)-q
4. (i)-p, (ii)-q, (iii)-r, (iv)-s

Q. A crystalline hydrated salt on being rendered anhydrous loses 45.6% of its weight.
The percentage composition of the anhydrous salt is:
$Al=10.5\%,K=15.1\%,S=24.8\%$ and oxygen $=49.6\%$
[Molar mass of $Al=27,K=39,S=32$].

What is the empirical formula of the hydrated salt?

1. $KAl{S}_2{O}_8.10H_{2}O$
2. $KAl{S}_2{O}_8.16H_{2}O$
3. $KAl{S}_2{O}_8.8H_{2}O$
4. $KAl{S}_2{O}_8.12H_{2}O$

Q. In a simple cubic lattice of anions, the side length of the unit cell is $3.0\stackrel{o}{A}.$ The diameter of the void in the body centre is

1. $0.46\stackrel{o}{A}$
2. $2.2\stackrel{o}{A}$
3. $4.9\stackrel{o}{A}$
4. $1.7\stackrel{o}{A}$

Q.

What is the difference between 1g atom of nitrogen and 1 g of nitrogen

Q.

At $25°\mathrm{C}$, $50$$\mathrm{g}$ of iron reacts with $\mathrm{HCl}$ to form ${\mathrm{FeCl}}_2$. The evolved ${\mathrm{H}}_2$ gas expands against a constant pressure of $1$ bar. The work done by the gas during this expansion is (round off to nearest integer) (given: $\mathrm{R}=8.14\mathrm{J}{\mathrm{mol}}^{-1}{\mathrm{K}}^{-1}$, assume ${\mathrm{H}}_2$ is an ideal gas, the atomic mass of $\mathrm{Fe}$is $55.85\mathrm{u}$) -

Q.

What are copper ions?

Q. A sample of limestone is $20\%$ pure. Find the mass of $C{O}_2$ produced by decomposing $40\text{g}$ of that sample of limestone.

1. $7.04\text{g}$
2. $1.76\text{g}$
3. $3.52\text{g}$
4. $3\text{g}$

Q.

A compound contains atoms of three elements A, B And C. If the oxidation number of A is +2, B Is +5 and that Of C Is −2, the possible formula of the compound is

Q. In hexagonal systems of crystals, a frequently encountered arrangement of atoms is described as a hexagonal prism. Here, the top and bottom of the cell are regular hexagons and three atoms are sandwiched in between them. A space-filling model of this structure, called hexagonal close-packed (HCP), is constituted of a sphere on a flat surface surrounded in the same plane by six identical spheres as closely as possible. Three spheres are then placed over the first layer so that they touch each other and represent the second layer. Each one of these three spheres touches three spheres of the bottom layer. Finally, the second layer is covered with third layer that is identical to the bottom layer in relative position. Assume radius of every sphere to be 'r'.

The empty space in this HCP unit cell is?

1. $74\%$
2. $47.6\%$
3. $32\%$
4. $26\%$

Q.

Write any two examples of compounds which have same molecular and empirical formulae.