NUMERICAL PRACTICE

Day 5
20.4.20


Good Morning Boys,
 Hope you have written the contents in your chemistry register. Today we will be learning about the laws of chemical combinations. You need to note down the notes given on the blog in your chemistry register. Those who have not made a register , you can compile the notes on pages for further reference.

Learning outcomes
students will be able to

• Recall law of  conservation of mass and law of constant proportion.
• Learn the law of gaseous volume and  Avagadros law .
• Apply concept to Numericals.

Law of Conservation of Mass

• This law was put forth by Antoine Lavoisier.
• Law of conservation of mass states that the matter can neither be created nor be destroyed.

Law of Definite Proportions

• This law was given by French chemist, Joseph Proust

• According to this law, a given compound always contains exactly the same proportion of elements by weight.

• He found that the composition of elements present in cupric carbonate was same for both the samples as shown below:-

Note: - It is  also referred to as law of definite composition.

Law of Multiple Proportions

This law was given by Dalton

• According to this law, if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers.
  • For example: - 
  • H2(2g) + (1/2)O2 (16g) ---------->H2O (18g)
  • H2(2g) + O2 (32g) --------------->H2O2 (34g)
  • The masses of oxygen O (16g and 32g) combine with the fixed mass of (2g) hydrogen H. Therefore the simple ratio is 16:32 or 1:2.

Gay Lussac’s Law of Gaseous Volumes

• law was given by Gay Lussac 
• He observed that when gases combine or are produced in a chemical reaction they do so in a simple ratio by volume provided all gases are at same temperature and pressure.
• For example: - Hydrogen  (100mL) + Oxygen (50mL)---> Water (100mL).
• The volumes of hydrogen (H) and oxygen (O) which combine together (i.e. 100mL and 50mL) bear a simple ratio of 2:1.

 Note : Volume is directly proportional to temperature at constant pressure .

Avogadro Law

•  Avogadro proposed that equal volumes of gases at the same temperature and pressure should contain equal number of molecules.
• He made distinction between atoms and molecules.

Numerical Questions ;

1.The following data are obtained when dinitrogen and dioxygen react together to form different compounds:
Mass of dinitrogen                Mass of dioxygen
(i) 14 g                                                       16g
(ii) 14 g                                                     32 g
(iii) 28 g                                                   32 g
(iv) 28 g                                                   80 g
Which law of chemical combination is obeyed by the above experimental data?

2.     10 grams of calcium carbonate (CaCO3) produces 3.8 grams of carbon dioxide (CO2) and 6.2 grams of calcium oxide (CaO). Represent this reaction in terms of law of conservation of mass.
Ans: According to law of conservation of mass:
Mass of reactants = Mass of products
∴ 10 gram of CaCO3 = 3.8 grams of CO2 + 6.2 grams of CaO
10 grams of reactant = 10 grams of products

Hence, it is proved that the law of conservation of mass is followed by the above reaction.

3.  Solve Gay-Lussac’s Law to get an expression for the unknown volume. Substitute the appropriate data into the formula.

V1 = 400mL V2 = ? mL T1 = 0oC T2 = 27oC

Solution: V1 = 400mL V2 = ? mL

T1 = 0oC + 273 = 273K

T2 = 27oC + 273 = 300K

Substitute all the values in the corresponding formula

V1T1=V2T2

V2 = (400 mL ×300 )/273

V2 = 439.56 mL

Thats all for the day. complete your work

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