Advertisements
Advertisements
Question
Derive the relationship between Relative molecular mass and Vapour density.
Advertisements
Solution
(i) The Relative Molecular Mass of a gas or vapour is the ratio between the mass of one molecule of the gas or vapour to the mass of one atom of Hydrogen.
(ii) Vapour density is the ratio of the mass of a certain volume of a gas or vapour, to the mass of an equal volume of hydrogen, measured under the same conditions of temperature and pressure.
Vapour Density (V.D.) = `"Mass of a given volume of gas or vapour at S.T.P"/"Mass of the same volume of hydrogen"`.
(iii) According to Avogadro’s law, equal volumes of all gases contain an equal number of molecules. Thus, let the number of molecules in one volume = n, then
(iv) V.D at STP = `" Mass of molecules of a gas or vapour at S.T.P"/"Mass of 'n' ‘molecules of hydrogen"`
Cancelling ‘n’ which is common, you get
V.D = `"Mass of 1 molecule of a gas or vapour at S.T.P."/"Mass of 1 molecule of hydrogen"`.
(v) Since hydrogen is diatomic
V.D. = `"Mass of 1 molecule of a gas or vapour at S.T.P."/"Mass of 2 atoms of hydrogen"`
(vi) By comparing the definition of relative molecular mass and vapour density we can write as follows.
V.D. = `"Mass of 1 molecule of a gas or vapour at S.T.P."/(2 × "Mass of 1 atom of hydrogen")`
Relative molecular mass (hydrogen scale) = `"Mass of 1 molecule of a gas or vapour at STP."/"Mass of 1 atom of hydrogen"`
(vii) By substituting the relative molecular mass value in vapour density definition, we get
Vapour density (V.D.) = Relative molecular mass/2
⇒ 2 × vapour density = Relative molecular mass of a gas.
APPEARS IN
RELATED QUESTIONS
Write down the name of a compound represented by the following formula:
CaCl2
Write down the name of a compound represented by the following formula:
KNO3
Give the name of the element present in the following compound:
Quick lime
State the term.
The number of atoms present in a molecule of an element _________
Define: Atomic number
Define: Mass number :
What is the atomicity of the following ?
- Oxygen
- Ozone
- Neon
- Sulphur
- Phosphorus
- Sodium
Write the formulae of the following compounds. Also name the elements present in them.
- Water
- Ammonia
- Methane
- Sulphur dioxide
- Ethanol
In what form does oxygen gas occur in nature ?
What is the difference between the molecule of an element and the molecule of a compound ? Give one
example of each.
One of the forms of a naturally occurring solid compound P is usually used for making the floors of houses. On adding a few drops of dilute hydrochloric acid to P, brisk effervescence are produced. When 50 g of reactant P was heated strongly, than 22 g of a gas Q and 28 g of a solid R were produced as products. Gas Q is the same which produced brisk effervescence on adding dilute HCl to P. Gas Q is said to cause global warming whereas solid R is used for white-washing.
- What is (i) solid P (ii) gas Q, and (iii) solid R.
- What is the total mass of Q and R obtained from 50 g of P ?
- How does the total mass of Q and R formed compare with the mass of P taken ?
- What conclusion do you get from the comparison of masses of products and reactant ?
- Which law of chemical combination is illustrated by the example given in this problem ?
Molecular compounds are usually formed by the combination between :
An element A forms an oxide A2O5.
What is the valency of element A ?
Why are the symbols and formulae of substances important?
State the main points of the contradiction of Dalton’s atomic theory by the Modern Atomic Theory.
State the atomicity of the following:
Neon
State the atomicity of the following:
Chlorine
Which of the following is a short and scientific way of representing one molecule of an element or compound?
State true of false. If false, give the correct statement.
NaCl represents one molecule of sodium chloride.
Classify the following molecules as the molecules of element or compound
| 1. |  |
|
| 2. |  |
|
| 3. |  |
|
| 4. |  |
Two elements sometimes can form more than one compound.
Define: Atomicity.
Give any two examples for heterodiatomic molecules.
Which of the following contains maximum number of molecules?
Write any two classifications of a molecule.
