1- Where are isotopes of the same element having different atomic masses placed in the periodic
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A-1) As the modern periodic table classifies the elements according to their atomic numbers, therefore the question of position of isotopes does not arise. Isotopes are the atoms of an element having the same atomic number but different atomic masses. Thus, all the isotopes will have the number of electrons (and therefore protons), and hence the problem of position of isotopes does not occur.
A-4) (a) A homologous series is a series of organic compounds which belong to the same family (i.e. possess same functional group) and show similar chemical properties. The members of this series are called homologue and differ from each other by the number of CH2 units in the main carbon chain. Following are the characteristics of a homologous series
- All homologues of a series have the same general formula e.g., all alkanes have the general formula Cn H2n + 2, alkyl halides have the general formula CnH(2n+1)X
- Each consecutive member differs from the next by one carbon atom and two hydrogen atoms (-CH2 group).
- The difference in the molecular mass between two consecutive homologues is 14 amu.
- The physical properties of homologues show a regular gradation.
- Homologues of a series have similar chemical properties.
(b) When ethanol is heated with concentrated H2SO4 at 443 K, we get ethene. Following is the chemical equation for the reaction
(c) Ethanol is an alcohol which has the OH functional group. Its chemical formula is C2H5OH. Ethanoic acid on the other hand is a carboxylic acid which has the chemical formula CH3COOH. A chemical test to distinguish between ethanol and ethanoic acid is sodium bicarbonate (NaHCO3) test. Ethanoic acid reacts with NaHCO3 to form sodium ethanoate and carbon dioxide according to the following reaction
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
that is brisk effervescence will be observed in the above reaction.
On the other hand, ethanol will not react with sodium bicarbonate and so no effervescence will be observed in the reaction.