Online Short Questions Preparations

How are enthalpy changes of reaction and energy of activation of reaction distinguished?

• Ans 1: Energy of Activation:"The minimum amount of additional kinetic energy required by the reactants in addition to average kinetic energy for effective collisions and product formation Energy of activation.
• Ans 2: Enthalpy Change of a reaction:
  "The enthalpy change occurs when the certain number of moles of reactants as indicated by the balanced chemical equation react together completely to give the products under standard conditions,i.e.25°C (298k) and one atmosphere pressure". Its units are kJ MOL^-
  
  

Define boiling point. Is it related with the external pressure?

• Ans 1: Boiling point is that temperature of the liquid at which the vapour pressure of the liquid is equal to the external pressure. If the external pressure is higher, then the boiling point of the liquid is increased. If the external presser is decreased, then the boding point decreases. The boiling of water is low at mountains. Due to the change in external pressure.

According to Bohr's model, the angular momentum of moving electron is a quantized. Justify it.

• Ans 1:

Differentiate between stationary and mobile phase?

• Ans 1: The solvent or the mixture of solvents used for the separation components in chromatography is called mobile phase. The phase over which mobile phase flows is stationary one. Water, ethyl alcohol etc. are some important Mobile phases while silica gel and filter paper are some important stationary phases.

Give the main uses of paper chromatrography.

• Ans 1:

  i. For the separation of purification of coloured organic compounds.

  ii.For checking the purity of the compounds.

  iii.In qualitative and quantitative analysis.

  iv.For the separation, purification and identification of products of reactions.

Why the melting boiling points of halogens increase down the group?

• Ans 1: The atomic sizes increase from fluorine to iodine. The number of shells increase, polarizability increase and the overlapping of the orbitals increase. This makes the melting and boiling points high down the group.

Give the main characteristics of the solvent used for crystallization.

• Ans 1:

  i. The solvent should dissolve a large amount of solute at high temperature.

  ii. The solvent should have no chemical reaction with solute.

  iii. It should not dissolve the impurities.

  iv. It should be cheap.

  v. It should not be inflammable.

Fractional crystallization technique is used to purify the chemical products.Justify?

• Ans 1: The separation of solid substance from a solution one by one on cooling is called fractional crystallization.Solubilities depends upon temperature.
  E.g.Solubility of KNO₃ Rapidly changes with temperature but solubility of KCI and Kbr changes gradually.Thus one substance may precipitate earlier by cooling, leaving behind others.

Why dipole-dipole forces are much stronger than dipole-induced dipole forces?

• Ans 1: In dipole-dipole forces, the atoms have sufficient partial positive and partial negative charges to attract each other. Where as in cuse of Londonforces no +ve or - ye change present apparently.

Why ethylene glycol is added in radiator of Automobile?

• Ans 1: The most important application of this phenomenon is the use of antifreeze in the radiator of an automobile.The solute is ethylene glycol, which is not only completely miscible with water but has a very low vapour pressure and non-volatile in character. When mixed with water it lowers the freezing point a swell as raised the boiling point.

Boiling points of liquid are increased when solute is added to them.Give reason?

• Ans 1: Because the vapour pressure of solvent decrease due to the pressure of solute.Therefore,we have to supply high temperature in order to equalized the vapour pressure of solvent to external pressure to boil it. This results in the increase of boiling point of solvent in the presence of solute.

• Ans 1:

Differentiate between ideals and non-ideal solutions?

• Ans 1: Ideal Solution:
  1. The solutions which obey Raoult's law are called ideal solution
  2. In these solution, enthalpy change is zero.

  
  
• Ans 2: Non-Ideal Solution:
  1. The solutions which do not obey Raoult's law are called non-ideal solution
  2. In theses solutions, enthalpy change is not zero.

Give two characteristics of enzyme catalyst?

• Ans 1: There are following characteristics of an enzyme.
  1. Enzymes catalysis is highly specific.
  2. Rate of enzymatic reaction is maximum at optimum temperature and pH.
  3. Enzymatic activities are enhanced by the presence of an activator.

Distinguish between actual and theoretical yield.

• Ans 1:

What is Moseley's law?

• Ans 1:

Define azeotropic mixture.Give two examples?

• Ans 1: Azeotropic Mixtures: The liquid mixtures which boil at constant temperature and distil over without changes in composition like a pure compound at any temperature is called azeotropic mixtures.e.g.HCI azeotropic mixture with water.

A mixture of NH₄OH and NH₄CI gives a basic buffer.Justify the statement ?

• Ans 1: A buffer which consists of a weak base and its salt with strong acid is called basic buffer.Since NH₄OH is a weak base and NH₄CI is its salt with strong acid.Therefore it is basic buffer.

What is absolute zero? What happens to real gases while approaching it?

• Ans 1: It is the lowest possible temperature which would have been achieved if the substance remains in the gaseous state. All the real gases are converted to liquids above this temperature. This -273.16°C is called zero absolute or zero Kelvin.

Calculate the S.I unit of R.

• Ans 1: