The document discusses the principles of chemical formulas, including empirical formulas, calculations for determining unknown compounds, and the relationship between moles and volume in gases. It also outlines the ideal gas equation, its limitations, and the modifications needed to accurately describe real gases. Key assumptions and practical techniques for measuring and calculating mass, volume, and concentrations in various chemical contexts are highlighted.

1. Amount of Substance
Content:

3. 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

5. Empirical Formulae

6. Mass relative to 1/12th
of Carbon-12 = 1u
Formula Unit

9. Steps For Empirical Formula Calculation of
Unknown Compounds.
• Step 1: Work out the molar ratio of the atoms.
• Step 2: Divide by the smallest number (in this case 0.025) to find the
whole number ratio.
• Step 3: Write the empirical formula.

10. In an experiment, 1.203 g of calcium combines with 2.13 g
of chlorine to form a compound [A,: Ca, 40.1; Cl, 35.5].

11. Analysis showed that 0.6175 g magnesium reacted with 3.995
g of bromine to form a compound. Find the empirical formula
of this compound. Atomic masses: Mg = 24.3 , Br = 79.9

12. Analysis of a compound showed the following percentage
composition by mass: Na = 74.2% , O = 25.8% (Ar: Na = 23 , O =
16)

13. A empirical formula of CH2 and a relative molecular
mass of 70. What is its molecular formula?

18. 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.

20. Weigh balance

23. A hydrated carbonate of an unknown Group 1 metal has the
formula X2CO3 .10H2O and is found to have a relative formula
mass of 286. What is the Group 1 metal?
Step 1: Work out the relative formula mass of the compound without the metal.
Step 2: Work out the atomic mass of the two Group 1 metal atoms.
Step 3: Look on the Periodic Table to find the element.

24. Practical Techniques for Measuring mass or find out
Formulae

25. Step 1: Calculate moles of Anhydrous CoCl2= C-A=
Step 2: Calculate moles of Water: B-C=
Step 3: Find the Smallest Whole Number Ratio
Step 4: Write down the value of X in CoCl2.XH2O
A
B
C
Mole=
Co= 58.93
CoCl2= ?

26. How accurate is an experimental Formula?
Assumption 1- All of the water has been lost.
Assumption 2- No Further decomposition

28. Mole and Volume

29. Using Volume to measure the amount of
substance
• Liquid and Gases are measured by using the volume.
• Volume can be converted into the amount of substance.
• =1ml
• 1 = 1 litre
• 1 = = 1000 ml = 1 litre

30. Converting Volume into Mole:
• Amount of Substance(n) mol , and Volume of Substance (V) has a link
with Concentration (c) mol .
• n=c × V
• We usually measure the volume in we need to convert it into by
dividing with 1000. So,
• n = c ×

31. Solution:

33. Standard Solution
• A standard solution is a solution of known
concentration or composition that is used in
analytical chemistry and various laboratory
applications as a reference or comparison
to determine the concentration or
composition of an unknown substance.
Volumetric Flask

35. Titration Apparatus

36. How to Calculate the mass of the sample to
prepare standard solutions of required molarity?

38. Moles and Gas volume
• It is difficult to measure the mass of gas but easy to measure the
volume of gas.
• At the same Temperature and pressure, equal Volumes of different
gases have the same no. of molecules or particles.

39. Molar Volume
• The molar gas Volume Vm is the volume of gas per mole of
gas molecules at standard temperature and pressure.
• Dependance:
• Temperature
• Pressure
• Note: Max. experiments are performed at RTP.

40. Molar Volume

41. Converting between the amount in moles
and volume of gases

44. What do you do when carrying out an experiment where
the gases are at different Temperature and Pressure?

45. The assumption for molecules to make up
an Ideal gas.

46. Conversion of quanti ties in the Correct units Pa, K, and before using the ideal gas equation.
No rmally wed o thiscon v ersion wh en an exp eriment is carry in g o u t

48. Incorrect Assumption
• Many people make the incorrect assumption that room temperature
is 25 °C (298K), the temperature often regarded as standard
temperature for chemistry. Using the ideal gas equation, you can
show that the molar gas volume at 25 °C an atmospheric pressure of
101 kPa is actually equal to 24.5

49. Find Relative molecular mass by Ideal gas
equation.
Application: You can use the ideal gas equation to find the relative
molecular mass of a volatile liquid.
Procedure: The unknown compound would need to be a liquid at room
temperature but have a boiling point below 100 °C so that it vaporizes.
1. Add a sample of the volatile liquid to a small syringe via a needle.
Weigh the small syringe.
Inject the sample into a gas syringe through the self-sealing rubber
cap. Reweigh the small syringe to find the mass of the volatile liquid
added to the gas syringe.
2. Place the gas syringe in a boiling water bath at 100 °C,
3. The liquid vaporizes and produces a gas and gas pressure is
recorded.

52. A 0.320 g sample of a volatile liquid was heated until it vaporized. The resulting
vapor then occupied 61.5 cm3 at 101 kPa and 100 °C.
Calculate the relative molecular mass of the volatile liquid.

53. The ideal gas equation relies on two key assumptions:
• Forces between molecules are negligible.
• Gas molecules have negligible size compared to the size of their
container.
These assumptions hold at low pressures and high temperatures when the
gas molecules are far apart and moving fast.

54. Improvement in Ideal gas equation:
Scientists have developed several improvements to the ideal
gas equation for real gases. In the real gas equation,
corrections have been made to take into account the volume of
gas molecules and intermolecular forces.

55. • The Van der Waals equation is one of the real gas equations used to describe the
behavior of real gases, taking into account the finite volume of gas molecules and
the presence of intermolecular forces. It is expressed as:
Where:
a and b are Van der Waals constants unique to each gas.
The Van der Waals equation incorporates two correction terms:
• a (the "attraction" term) accounts for the attractive forces between gas molecules. It
is a measure of how strongly the gas molecules are attracted to each other.
• b (the "repulsion" term) accounts for the finite volume occupied by gas molecules.
It represents the effective volume excluded by the gas molecules themselves.

56. Difference between ideal and real gas
Characteristic Ideal Gas Real Gas
Particle Volume Negligible (treated as point masses) Significant (finite volume)
Intermolecular Forces
Negligible (no forces between
particles)
Present (attractions/repulsions)
Behavior at High Pressure Follows ideal gas law
Deviates from ideal behavior due to
particle volume and interactions
Behavior at Low Temperature Follows ideal gas law
Deviates from ideal behavior due to
reduced kinetic energy and
condensation
Ideal Gas Law Validity
Ideal gas law holds well at low
pressures and high temperatures
Real gases become more ideal at
low temperatures and high
pressures

57. Difference Between ideal and Real gas equation
Characteristic Ideal Gas Equation Real Gas Equation
Formula PV = nRT
Various forms (e.g., Van der Waals,
Redlich-Kwong)
Applicability Ideal gases Real gases
Assumptions Negligible particle volume, no
intermolecular forces
Accounts for particle volume and
intermolecular forces
Conditions Low pressures, high temperatures
High pressures, low temperatures,
deviations from ideal behavior
Deviations from Ideal Behavior Ideal behavior assumed
Describes deviations from ideal
behavior

58. Predict the conditions of pressure and temperature that
cause the ideal gas equation to break down.
Explain your answer.
Answer: The ideal gas equation breaks down under high pressure, low
temperature, and high gas density conditions because it does not
account for the real-world behaviors of gas molecules, including volume
exclusion and intermolecular forces. In such cases, more complex
equations of state, like the Van der Waals equation are used to describe
the behavior of real gases more accurately.

59. Volume Exclusion
Volume exclusion, also known as the excluded volume effect, refers to
the idea that in a real gas, molecules have finite volumes and cannot
occupy the same space simultaneously. This concept is in contrast to the
ideal gas assumption, which treats gas particles as point masses with
zero volume. Volume exclusion becomes significant at high gas
densities and is one of the factors that can cause deviations from ideal
gas behavior.

60. 1: Calculate the amount of substance, in moles, in:
50 of a 1.00 mol solution.
n = c ×
2: Calculate the concentration, in g , for:
2.00 mol of NaOH in 4.00 of solution.