This ppt is About amount of substance from OCR chemistry with practice.

1. Amount of Substance
Content:

2. What is Substance?
A substance is a type of matter that
has specific chemical and physical
properties. It refers to a particular
kind of material that is uniform in its
composition and characteristics.
Substances can be elements or
compounds.

3. Substance
Molecule
Atom

4. What is the mass
of Atom?
→The sum of Electron,
proton, and neutron

5. Mass Defect:

6. Relative Atomic Mass (RAM)
Atoms have a very small mass. It is not practically possible to
measure its actual mass or use its actual mass anywhere.
Standards
• carbon-12 isotope = international standard for the measurement of atomic
masses.
• The atomic mass unit u, amu
• The mass of a carbon-12 isotope is defined as exactly 12 atomic mass units
(12u).
• The standard mass for atomic mass is 1u, the mass of 1/12 th of an atom of
carbon-12.
• On this scale, 1u is approximately the mass of a proton or a neutron.

7. Definition
The RAM (Ar) of an atom is the average mass of one atom of that
element compared to 1/12th of the mass of one carbon-12 atom.
Or
Relative Atomic Mass is the weighted average mass of the atoms in a
naturally occurring sample of an element, compared to 1/12th of the
mass of a carbon-12 atom. The RAM is usually given in atomic mass
units (u) or grams per mole (g/mol).
To calculate the Average atomic mass
= (Sum of (Isotopic Mass × Abundance)) / 100

8. Formula
To calculate the RAM of an element:
RAM= Average masses of one atom of the element /1/12th of C-12
Example:
Isotope O-16: Mass = 15.9949 u, Abundance = 99.76%
Isotope O-18: Mass = 17.9992 u, Abundance = 0.04%
RAM = (15.9949 × 99.76 + 17.9992 × 0.04) / 100 ≈ 15.999 u
(Average mass)
one atom of Oxygen is 16 times heavier as 1/12th of an atom of C-12
Thus Oxygen has a RAM of 16u.

10. Substance in gram = 1 mole = 6.02×1023
Particles
Note: (Particles are Atom, Ions, and molecules)
Representation= n = Amount of substance = Mole
Formula:
mole= n = m
M
M= molar mass
m= given mass sample

11. Mole

12. Avogadro’s Number NA

13. Mass= 96g
Carbon= 12g/mol
Mole?

14. Assignment

16. A chemical formula is a symbolic
representation that expresses the
composition of a chemical substance
using chemical symbols and numbers.
This type of formula provides the
actual number of each type of atom in
a molecule of the compound.
The empirical formula represents the
simplest, most reduced ratio of different
elements in a compound or It gives the
lowest whole-number ratio of the elements
present in the compound
The simplest ratio
of atoms of an
element in a
compound
Number of atoms of
each element in a
molecule

19. Mass relative to 1/12th
of Carbon-12

27. Water of crystallization, also known as water of hydration, these are water molecules that are
structurally incorporated into the crystal lattice of a chemical compound.
This help to maintain shape of crystal in some salts and complex metal oxides.