Determine the empirical formula of an oxide of iron, which has 69.9% iron and 30.1% dioxygen by mass.
Solution and Explanation
% of iron by mass = 69.9 % [Given]
% of oxygen by mass = 30.1 % [Given]
Relative moles of iron in iron oxide:
\(=\frac{ \% \text{of iron by mass} }{ \text{Atomic mass of iron}}\)
\(= \frac{69.9 }{ 55.85}\)= 1.25
Relative moles of oxygen in iron oxide:
\(= \frac{\% \text{of oxygen by mass} }{ \text{Atomic mass or oxygen}}\)
\(= \frac{30.1 }{ 16.00}\)
= 1.88
Simplest molar ratio of iron to oxygen:
\(= 1.25\ratio 1.88\)
\(= 1\ratio 1.5\)
\(≈2\ratio 3\)
∴ The empirical formula of the iron oxide is \(\text{Fe}_2\text{O}_3\).
Top Questions on Atomic and Molecular Masses
- How many significant figures should be present in the answer of the following calculations?
- \(\frac {0.02856 × 298.15 × 0.112}{0.5785}\)
- \(5 × 5.364\)
- \(0.0125 + 0.7864 + 0.0215\)
- CBSE Class XI
- Chemistry
- Atomic and Molecular Masses
- Which one of the following will have the largest number of atoms?
- CBSE Class XI
- Chemistry
- Atomic and Molecular Masses
- If the speed of light is 3.0×108 ms–1, calculate the distance covered by light in 2.00 ns.
- CBSE Class XI
- Chemistry
- Atomic and Molecular Masses
- In three moles of ethane \((\text{C}_2\text{H}_6)\), calculate the following:
(i) Number of moles of carbon atoms.
(ii) Number of moles of hydrogen atoms.
(iii) Number of molecules of ethane.- CBSE Class XI
- Chemistry
- Atomic and Molecular Masses
- Calculate the atomic mass (average) of chlorine using the following data:
% Natural Abundance Molar Mass
\(^{35}\text{Cl}\) 75.77 34.9689
\(^{37}\text{Cl}\) 24.23 36.9659- CBSE Class XI
- Chemistry
- Atomic and Molecular Masses
Questions Asked in CBSE Class XI exam
- Find the sum to indicated number of terms in each of the geometric progressions in 1, – a, \(a^2\), –\(a^3\), ... n terms (if a ≠ – 1).
- CBSE Class XI
- geometric progression
- Find n if n-1P3: nP3 = 1: 9.
- CBSE Class XI
- Permutations
- Give a brief description of the principles of the following techniques taking an example in each case.(a) Crystallisation (b) Distillation (c) Chromatography.
- CBSE Class XI
- Organic Chemistry- Some Basic Principles and Techniques
- Three reasons why the author’s grandmother was disturbed when he started going to the city school.
- CBSE Class XI
- The Portrait of a lady
- Draw diagrams showing the formation of a double bond and a triple bond between carbon atoms in \(C_2H_4\) and \(C_2H_2\) molecules.
- CBSE Class XI
- Bond Parameters
Concepts Used:
Structure of Atom
Atomic Structure:
The atomic structure of an element refers to the constitution of its nucleus and the arrangement of the electrons around it. Primarily, the atomic structure of matter is made up of protons, electrons and neutrons.
Dalton’s Atomic Theory
Dalton proposed that every matter is composed of atoms that are indivisible and indestructible.
The following are the postulates of his theory:
- Every matter is made up of atoms.
- Atoms are indivisible.
- Specific elements have only one type of atoms in them.
- Each atom has its own constant mass that varies from element to element.
- Atoms undergo rearrangement during a chemical reaction.
- Atoms can neither be created nor be destroyed but can be transformed from one form to another.
Cons of Dalton’s Atomic Theory
- The theory was unable to explain the existence of isotopes.
- Nothing about the structure of atom was appropriately explained.
- Later, the scientists discovered particles inside the atom that proved, the atoms are divisible.
Subatomic Particles
- Protons - are positively charged subatomic particles.
- Electron - are negatively charged subatomic particles.
- Neutrons - are electrically neutral particles and carry no charge
Atomic Structure of Isotopes
Several atomic structures of an element can exist, which differ in the total number of nucleons.These variants of elements having a different nucleon number (also known as the mass number) are called isotopes of the element. Therefore, the isotopes of an element have the same number of protons but differ in the number of neutrons. For example, there exist three known naturally occurring isotopes of hydrogen, namely, protium, deuterium, and tritium.