first year Basic concepts short Questions and answers

CHAPTER NO. 01       F.Sc. 1st Year

BASIC CONCEPT

Short Answers Questions:

Q.1. What is chemistry?

Ans: Chemistry is the branch of science which deals with study of the composition,structure, properties and changes of matter and laws which governs these changes.

Q.2. What is an Atom?

Ans:  The smallest particle of an element which retains identity of an element and can take part in a chemical reaction is called an Atom. It may or may not exist independently. e.g. He,Ne , have independent existance, while atoms of H,O, And N donot exist independently.

Q. 3.  Define molecule.

Ans: The smallest particle of a pue substance which can exist independently is called Molecule.  Molecules of element may contain one, two. Or more of the same type of atoms. e.g. He, O2, Cl2, P4, S8, etc. While molecule of compound contains more than one type of molecule. e. g. H2O, HCl, NH3, H2SO4.

Q.4. What is Atomicity?

Ans: The number of atoms present in a molecule is called its Atomicity. Thus Molecules may be monoatomic, diatomic, and triatomic depending upon number of atoms contains one. Two and three respectively.

Q. 5. What is an Ion?

Ans: Specie which carry either positive or negative charge is called an ion.  An ion with positive charge called cation e.g Na⁺,  K⁺,  Ca⁺², Al⁺³ etc.  An ion carrying negative charge called Anion.  e. g Cl^-,  S^-2, Br^-  etc.

Q. 6. What are Molecular Ions.?

Ans: Molecular Specie containing either positive or Negative charge is Called Molecular Ion.  e. g. CH⁴⁺, CO⁺,  N²⁺, O²⁺,. These Ions can be generated by passing beam of electrons,  alpha particle,  or X rays through a gas.

Q. 7. Define relative atomic mass.

Ans: The mass of an atom of an element as compared to the mass of an atom of Carbon taken as 12 is called  relative atomic mass.

Q. 8. What is atomic mass unit (amu)?

Ans: The unit used to express the relative atomic mass is called atomic mass unit and is 1/12th of the mass of carbon atom. Amu is equal to 1.661 x 10²⁴g or 1.661 x 10²⁷Kg

Q.9. What is ment by isotopes?

Ans.  Atoms of same element that have same atomic number but different atomic masses are called isotopes. Carbon has three isotopes C12, C13, C14 etc.

Q. 10. Why isotopes have same chemical properties and different physical properties?

Ans.  Chemical properties depends upon electronic configurations and Isotopes of the same elements have same arrangements of electrons or in other words they have same electronic configurations thats why isotopes of same elements have same chemical properties a d different physical properties.

Q.11. The atomic masses may be in fractions why?

Ans. The atomic masses depends upon the number of possible isotopes and their natural abundance. Therefore average atomic masses of elements in fractions.

Q. 12. What is fractional atomic masses ?

Ans. Average atomic masses of elements which are in fractions are called fractional atomic masses.

Q. 13. What is mass spectrometer?

Ans. Mass spectrometer is an instrument which is used to determine the atomic masses of different isotopes of an element.

Q14. What is mass spectrometry?

Ans.  Mass spectrometry is an analytical method used to determine the exact masses of different isotopes of an elements.

Q. 15. Write down principle of mass spectrometer.

Ans.  The gaseous sample of substance is introduced into the ionization chamber and a beam of electrons is made to fall on gas vapours which produces positive ions. These ions are accelerated towards negatively charged grid. Then the beam of ions passed through magnetic fields of strength H, which deflect the ions to a curved path. Extent of deflection depends upon m/e value. Ions with definite m/e enter into electrometer which gives the relative abundance of ions of definite m/e value.

Q. 16. What is the function of electrometer in mass spectrometer?

Ans.  Electrometer is also called ion collector.  Develops the electric current which is proportional to the number of ions falling on it and current strength in each case gives the relative abundance of each isotopes.

Q. 17. What is mass spectograph?

Ans.  A graph plotted between m/e of positive ions on abscissa (x-axis) and relative abundance n ordinate(y-axis). Graph is recorded in the form of peaks.

Q. 18. Define Empirical formula how it is related with molecular formula?

Ans.  A chemical formula which gives us the whole number ratio of atoms of each element in compound is called Empirical formula.

Molecular formula = n x Empirical formula

n= simple integr i.e 1,2,3...

 n= Molecular mass/Empirical formula mass

The Empirical formula of Benzene is CH while molecular formula is C₆H₆.

Q. 19. Define Molecular formula with examples.

Ans.  A chemical formula which indicates actual or total number of atoms present in a molecule is called molecular formula. i. e.  Molecular formula for Benzene is C₆H₆. While that of Glucose is C₆H₁₂O₆.

Q.20.what is mole?

Ans.  Atomic mass, Molecular mass or formula mass of substance when expressed in grams is called a mole of that substance.

Number of moles = Given mass in grams/ Molar Mass

*Molar mass may be atomic mass, molecular mass or formula mass.

Q. 21. Define gram atom, gram molecule, gram formula?

Ans.       AtomIc mass when expressed in grams is called gram atom.

Molecular mass when expressed in grams is called gram molecule.

Formula mass expressed in grams is called gram formula.

Q.22. Define Avagadro's number with examples.

Ans.  The number of particles (atoms, ions or molecules)  in one gram atom  of an element, one gram molecule of a compound or one gram ion of a substance, respectively is called Avagadro's number.  It is denoted by NA and it's value is found to be 6.02 x 10²³.

Examples:

1.008 g of hydrogen = 1mole of H =   6.02 x 10²³ atoms of H

18g of H₂O = 1mole of water          =   6.02 x 10²³ molecules of H₂O

96 g of SO₄^2- = 1mole of SO₄^2-         =   6.02 x 10²³ ions of SO₄^2-

Q. 23. Define molar Volume with examples.

Ans.       The Volume of 22.414 dm³ occupied by one mole of any gas at stp is called molar volume.

2.016g of H₂ = 1mole of H₂ = 22.414 dm3 of H₂ at STP

16g of CH₄ = 1mole  of CH₄ = 22.414 dm3 of CH₄ at STP

Q. 24. 23g Na and 283g of uranium  have equal number of atoms justify.

Ans.  23g of Na = 1mole of Na = 6.02 x 10²³ atoms

          238g of U = 1mole of U = 6.02 x 10²³ atoms.

Na &  U have equal number of Avagadro's particles.

Q. 25. Mg atom is twice heavier than that of Carbon. Justify.

Ans.  The Atomic mass of Mg is 24amu Which is twice in mass as compared to the atomic mass of carbon  i.e 12 amu.  Therefore Mg atom is twice heavier than that of Carbon.

Q. 26. 2g of H₂, 16 g of CH₄ and 44g of CO₂ occupy separately the volume of 22.414 dm3, although the size and mass of these gases are different. Justyfy.

Ans.  The difference in masses and sizes of molecules of gases donot effects the volume of gases. One mole of any gas at STP occupies a volume of 22.414 dm3.

Therefore  2 g of H₂,  16g of CH₄ and 44g of CO₂ having 1mole,  occupy same volume.

Q. 27. 1mole of H₂SO₄ completely reacts with 2 mole of NaOH. Explain with the help of Avagadro's number.

Ans.  H₂SO₄   +    2NaOH                               Na₂SO₄     +   2H₂O

1mole of H₂SO₄ produces 2 mole of H⁺ ions (2 x 6.02 x 10²³). Thus it requires 2mole of OH^-  ion

 ( 2 x 6.02 x 10²³)from the base for neutralization.

Q.28. NaCl has 58.5 amu as formula mass and not the molecular mass. Justyfy it.

Ans.  NaCl is ionic compound and does not exist in the molecular form. Therefore NaCl is a formula unit and has 58.5 amu as formula mass and not molecular mass.

Q. 29. Calculate the mass in grams of 10^-3 moles of H2O.

Ans.  Mass of H2O = no. Of moles X Molar Mass.

                                  = 10^-3 mole x 18g mol^-1 = 1.8 x 10^-2 g = 0.018g

Q. 30. What is stoichiometry?

Ans.  The study of quantitative relationship between the amounts of reactants and products in a balanced  chemical equation is called stoichiometry.

Q. 31. What is law of conservation of mass?

Ans. It states that the matter neither be created nor destroyed but can change from one form to another.

Q. 32. What is law of definite proportion.?

Ans. It states that the atoms combine to form molecules with definite proportions i.e H₂O Hydrogen and Oxygen combine with 2:1.

Q. 33. What is limiting reactant? How it controls the reaction?

Ans.  The reactant which is in limited extent and completely consumed in a reaction is called limiting reactant. Because it determines the amount of product formed.  Once the limiting reactant is consumed  the reaction stops and no additional product is formed.  Hence the limiting reactant control the reaction.

Q. 34. Concept of limiting reactant is not applicable to reversible reactions. Explain it?

Ans. The concept of limiting reactant is not applicable to reversible reaction because certain amounts of each reactant left behind at the equilibrium state  and thus any reactant  is not completely consumed as restricted by quantity of the limiting reactant in reaction.

Q. 35. 11g carbon is reacted with 32g of O2 to give CO₂.  Which is limiting reactant.

Ans.                C    +    O₂                             CO₂

        1 mole of C (12g) allow it to react with one mole of O₂ (32g)  to give 1mole of CO₂ (44g)

  According to balanced equation.  Since less amount of carbon is used so carbon is limiting reactant.

Q36. Distinguish between actual yield and theoretical yield.

Ans.  Amount of products obtained actually are called actual yield. Amount of products calculated by balanced equation called theoretical yield.

Q. 37. How can the efficiency of reaction calculated?

Ans. The efficiency of reaction can be calculated by  comparing the actual and theoretical yield in the form of percentage yield.

  % yield   =   Actual yield /theoretical yield  x 100

Q. 38. Why actual yield is always less than theoretical yield.

Ans.  Due to following reasons.

1. The mechanical loss of products(due to inexperienced worker) during the process like filtration, distillation, washing, and crystallization.

 2. The reacts may form another product i.e side reaction may start.

                3. Reversibility of reactions.

Q. 39. During combustion analysis which absorber absorbs H₂O vapors and CO₂ gas.

Ans.  In the process of combustion analysis CO₂ absorbs by 50% KOH and H₂O vapours absorbs by Mg (ClO₄).

Q. 40. What are the assumptions of stoichiometry?

Ans.  Following are the assumptions of stoichiometry

1. Reactants ate completely converted into products.
2. No side reaction occurs.
3. The law of conservation of mass and law of definite proportions are obeyed.

Q41. Which type of relationship can be studied by the help of a balanced equation from stoichiometry.

Ans:

1. Massmass relationship
2. Mass-mole relationship
3. Mass- Volume relationship
4. Volume - Volume relationship.

Q. 42. How limiting reactant can be identified?

Ans.

1.       Determine the number of moles of from the given amount of reactant.

2.       Find number of mole of products from balanced equation.

3.       Identify the reactant which produces the least amount of product as limiting reactant.

 Q. 43. Give reason that law of conservation of mass obeyed during stoichiometric calculations.

Ans.  It is assumed in stoichiometric calculations that atoms neither created nor distroyed during chemical change. Hence total mass of products of chemical reactions is same as total mass of reactants.  The changes that occur during reactions involved rearrangement of atoms. (supports law of conservation of mass).

Q. 44. Many chemical reactions taking place in our surrounding involves the limiting reactant. Justyfy.

Ans.   Many reactions in our surrounding involves limiting reactant i.e Burning process.  Oxygen is in excess in air while natural gas or wood or paper  are in limited quantities.

Nitrogen  and Oxygen  of atmosphere reacta to form  NO due to electrical discharge of lightening.  In this reaction oxygen is limiting reactant.

Q. 45. What is mathematical relationship between m/e?

Ans.  Mathematical relationship between m/e is

 m/e = H₂r₂/2E

H is strength of magnetic field,  E is the strength of electric field.  r is the radius of circular path.  If E is increased by keeping H constant then radius will increase and particular ion falls at different place as compared to first place.