Monday, 20 April 2020

1st year Chemistry Chapter 1 Short Questions Notes

1st year Chemistry Chapter 1 Short Questions Notes

Looking for the 11th class chapter 1 Basic Concepts of chemistry notes? Here we have shared the 1st year Chemistry Chapter 1 Short Questions Notes.

01. 23 g of sodium and 238 g of uranium have an equal number of atoms in them. Explain (imp) 23 g of Na = 1 mole
 238 g of Uranium = 1 mole
 since 1 mole of each element has Avogadro’s number of atoms. Hence, 23g of Na (1 mole) and 238g of Uranium (1 mole) contain an equal number of atoms i.e. 6.02 × 1023.

02. Mg atom is twice heavier than carbon. Explain (imp) 
The atomic mass of an atom is the mass that is obtained after comparing it with carbon-12. The atomic mass of Mg comes to be 24 amu and that of carbon is 12 amu. It means that Mg is twice heavier than carbon.

 03. 180 g of glucose and 342 g of sucrose have the same no of molecules but different no of atoms present in them. Explain
 180 g of glucose = 1 mole of glucose
 342 g of sucrose = 1 mole of sucrose
 Both are one mole and have 6.02 x 1023 no. of molecules. The molecule of glucose (C6H12O6) contains 24 atoms but that of sucrose (C12H22O11) contains 45 atoms.

06. Two grams of H2, 16 g of CH4 and 44g of CO2 occupy separately the volume of 22.414 dm3, although the size and masses of three gases are very different from each other. Explain.
 2 g of H2 = 1 mole of H2
 16 g of CH4 = 1 mole of CH4
 44 g of CO2 = 1 mole of CO2
 One mole of any gas at STP has 22.414 dm3 volumes. All the gases have one mole hence contains 22.414 dm3 volume.
 In gases, the distance between two molecules is approximately 300 times greater than their diameter. Thus, the volume occupied by gas molecules doesn’t depend upon size or mass of gas molecules and it only depends upon the number of molecules
 07. The Law of conservation of mass has to be obeyed during the stoichiometric calculation.
 According to the law of conservation of mass, the number of reactants and products remain the same during a chemical reaction. Now in stoichiometric calculations, it is supposed that amount of reactants and products do not change during a chemical reaction, otherwise calculate may not be possible. So, during stoichiometric calculations balanced equation is used to ensure that the law of conservation of mass obeyed.
 08. Many chemical reactions taking place in our surroundings involve the limiting reactants.
 (a) Burning of natural gas involves limiting reactant. Oxygen in the atmosphere is in excess amount but natural gas consumes earlier hence it is a limiting reactant.
 (b) Burning of petrol in an engine also involves limiting reactant. Oxygen is in excess amount but petrol consumes earlier hence it is a limiting reactant.
 09. No individual neon atom in the sample of the element has a mass of 20.18 amu.
 Neon has three isotopes 20Ne, 21Ne and 22Ne with relative abundance as 90.92%, 0.26%, and 8.82%. The average atomic mass of Ne is 20.18 amu. This average mass depends upon the no. of possible isotopes and their relative abundance.

 11. One mole of water has two moles of bonds, three moles of atoms, ten moles of electrons and twenty-eight moles of total fundamental particles in it. Explain.
 The structure of water is H x ------- O -------- x H In one mole of water, moles of bonds = 2 mole In one mole of water, moles of O = 1 mole In one mole of water, moles of H = 2 moles In one mole of water, moles of atom = 3 moles In one mole of water, moles of electrons = 10 moles (8 moles of O and 2 moles of H).
 In one mole of water, moles of fundamental particles of O = 8P+8N+8e- = 24 In one mole of water, moles of fundamental particles of H = 2P+2e- = 4 Total fundamental particles = 28.

 13. Under what condition ions are produced?
 Ions from Elements Cations (positive ions) are formed by the removal of electrons. During this process, energy is absorbed and it is an endothermic process. Anions (negative ions) are formed by the addition of electrons. During this process, energy is released and it is an exothermic process. Ions from an Ionic compound produced ion when dissolved in water or when it is infused state. Ions from Molecular compound  Molecular compound produced ions when a bombardment of electrons or passing of α-rays takes place on them.
 14. How limiting reactant controls the number of products?
 A limiting reactant is one which is consumed earlier and stops the further formation of products although the excess reagent is present in the vessel. So, limiting the reactant controls the formation of the product.

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