0| Importance of this topic: i) Law of Equivalence is one of the most important concepts of Chemistry ii) Allow to find equivalent weights of different compounds and apply the law of Equivalence for Stoichiometric problems iii) Will be able to calculate Normality of solutions |
1.1 Equivalent Weight of an Element in a compound which have H.
Equivalent of a substance is defined as the amount of it which combines with one mole of hydrogen atoms or replaces the same number of hydrogen atoms in a chemical reaction.
The weight in grams of one equivalent is called the equivalent weight in grams
Q1. Find the equivalent weight of the following elements in bold
| H2O | NH3 | HBr |
1.2 Equivalent Weight of an Element in a compound which do not have H.
Law of Equivalence : The law states that one equivalent of an element combines with one equivalent of the other.
Q2. Find the equivalent weight of the following elements in bold
| Al2O3 | FeO | Fe2O3 |
Note: An element can have more than one value of Equivalent weight.
1.3 Equivalent of a compound taking part in a reaction:
The equivalent weight in grams of a compounds taking part in a reaction is the weight of the compound which combines with one equivalent of another compound..
Q3. Find the equivalent weight of Na2CO3 for the following reactions
| 1. Na2CO3 + 2HCl à 2NaCl + CO2 + H2O
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| 2. Na2CO3 + HCl à NaHCO3 + NaCl
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Note: The equivalent weight of a compound taking part in a reaction should be determined from the chemical equation as Equivalent weight of a compound depends upon the Stoichiometry of the reaction.
To calculate the equivalent weight of any substance taking part in a reaction we generally use the following expressions of the law of equivalence . For a reaction
aA + bB à cC + dD.
= = =
1.4: Equivalent wt of an acid
1.5 Equivalent wt of a base
1.6 Equivalent wt of a salt:
Or,
1.7 Equivalent wt of a oxide:
Practice Problems ( Try to understand these problems and take time to solve)
| P1 | If W1 and W2 are the weights of two reactions in any reaction having their equivalent weights E1 and E2 respectively which of the following equations represents the law of equivalence correctly |
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| P2 | 12 gram of an element combines with 32 grams of oxygen. What is the equivalent weight of the element is the equivalent weight of oxygen is 8? |
3 |
| P3 | What are the equivalent volumes of Hydrogen, Oxygen and Nitrogen? | 11.2L 5.6L 3.73L |
| P4 | How many molecules are present in 1 equivalent each of hydrogen Oxygen and nitrogen? | NA/2 NA/4 NA/6 |
| P5 | If 0.5 equivalent of H2C2O4 undergoes complete dissociation what will be the number of equivalent of H+ and C2O4-2 | 0.5 eq |
| P6 | Calculate the number of equivalents in 1 mole of Oxygen molecules | 4 |
| P7 | The two acids H2SO4 and H3PO4 are neutralized separately by the same amount of an alkali when sulphate and dihydrogen orthophosphate are formed respectively. Find the ratio of masses of H2SO4 and H3PO4. |
1/2 |
| P8 | Find the equivalent weight of H3PO4. in the reaction Ca (OH)2 + H3PO4 = CaHPO4 + 2H2O | 49 |
| P9 | Equivalent weight of S in SCl2 to is 16, what is the equivalent weight of S in S2Cl2 ? | 32 |
| P10 | The equivalent weight of a metal is double than that of an oxygen. How many times is the weight of its oxide greater than the weight of the metal? |
1.5 |
| P11 | 1.60 gram of Calcium and 2.60 gram of Zinc when treated with an acid in excess separately produce the same amount of hydrogen. If the equivalent weight of Zinc is 32.6 what is the equivalent weight of Calcium? |
20 |
| P12 | 1 g of an alloy of Al and Mg when treated with excess of dilute HCl forms magnesium chloride, aluminium chloride and hydrogen. the evolved hydrogen collected over Hg at 00C has a volume of 1.20 L at 0.92 atmosphere pressure. Calculate the composition of the alloy ( At wt Al = 27, Mg =24) |
Al = 0.55g Mg= 0.45g |
| P13 | 0.376g of Al reacts with an acid to displace 0.468L of hydrogen at NTP. Find the equivalent volume of hydrogen, if the Equivalent weight of Aluminium is 9 |
11.2L |
| P14 | 1L of oxygen at NTP weighs 1.46 gram. How many L of oxygen are needed for the combustion of 21 gram of Mg whose equivalent weight is 1/2 mole |
9.59L |
| P15 | Dry H2 was passed over 1.58 g of red hot copper oxide till all of it is completely reduced to 1.26 grams of copper . If in this process 0.36 gram of H2O is formed ,what will be the equivalent weight of Cu and O? |
8 |
| P16 | The equivalent weight of Cl is 35.5 and the equivalent weight of copper chloride is 99.5. Find the formula of copper chloride if the atomic weight of copper is 63.5 and chlorine is 35.5. |
CuCl |
| P17 | 4.215g of a metallic carbonate was heated in a hard glass tube and the carbon dioxide evolved was found to measure 1336 ml at 270C and 700 mm pressure . What is the equivalent weight of the metal? |
12.15 |
| P18 | 0.324 g of copper was dissolved in nitric acid and the copper nitrate so produced was burnt till all copper nitrate converted to 0.406 gram of copper oxide. Calculate the equivalent weight of copper. |
31.60 |
| P19 | 0.13g of copper when heated with silver nitrate solution displace 0.433 g of silver. 0.13 g of aluminium when treated with copper sulphate solution displace 0.47 g of copper. 1.17 gram of aluminium displaces 0.13 gram of hydrogen from an acid. Find the equivalent weight of silver if equivalent weight of Copper and Aluminium are not known |
108.5 |
| P20 | 1 gram of Mg is burnt in a closed vessel which contains 0.5 gram of O2. i) Which reactant is left in excess? ii) Find the weight of excess reactant. iii) How many millilitres of 0.5 N H2SO4 will dissolve the residue In the vessel | Mg 0.25g 166.6 ml |
| P21 | 448 ml of SO2 at NTP is passed through 200 ml of 0.2 N solution of NaOH. Find the weight of the salt formed. | 2.08 g |
