Chemistry Test - 6

A galvanic cell or simple battery is made of two electrodes. Each of the electrodes of a galvanic cell is known as a half cell. In a battery, the two half cells form an oxidizing-reducing couple. 

When two half cells are connected via an electric conductor and salt bridge, an electrochemical reaction is started.

The given reaction is, 

\({Pt}^{2+}+2 {Cl}^{-} \rightarrow {Pt}+{Cl}_{2}, E_{\text {cell }}^{0}=-0.15 {~V}\)

Anode: 

\(2 C l^{(-)} \rightarrow C l_{2}+2 e^{-}\) 

Cathode:

\(P t^{2+}+2 e^{-} \rightarrow P t\) 

The EMF of a cell is given by the following expressions:

EMF of a cell \(=\) Reduction potential of cathode \(-\) Reduction potential of anode 

\(\therefore E_{c e l l}=E_{R}-E_{L}\) 

\(-0.15=E_{P t^{2+} / P t}-E_{C l_{2} / C l^{(-)}}\)

 \(-0.15=1.20-E\) 

\(E=1.20+0.15\) 

\(E=1.35 V\)

Given reaction,

\(4 \mathrm{Fe}+3 \mathrm{O}_{2} \longrightarrow 4 \mathrm{Fe}^{+3}+6 \mathrm{O}^{2-}\)

Clearly, given reaction is a redox reaction in which, Fe gets oxidised to \(\mathrm{Fe}^{+3}\) by losing of three electrons, and \(O_{2}\), gets reduced to \(O^{2-}\).

Thus, Metalliciron \((F e)\) is a reducing agent and \(\mathrm{Fe}^{+3}\) is an oxidising agent.

The physical adsorption of gases on the solid surface is due toVan der wall's force.

When the force of attraction existing between adsorbate and adsorbent are weak Van der wall's of attraction, the process is called Physical Adsorption or Physisorption. When the force of attraction existing between adsorbate and adsorbent are chemical forces of attraction or chemical bond, the process is called Chemical Adsorption.

Neutral ligand means ligand with no charge on it.

Example: H₂O, NH₃, CO, C₂ H₄...

ONO^- has a charge on it, therefore it is not a neutral ligand.

Benzene forms Nitrobenzene on reaction with conc. HNO₃/H₂SO₄, in the reaction HNO₃ acts as a base.Proton donor is acids and proton acceptor is bases. Conc. \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and conc. \(\mathrm{HNO}_{3}\) react in the following manner:

\(\mathrm{HNO}_{3}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{H}_{2} \mathrm{NO}_{3}^{+}+\mathrm{HSO}_{4}^{-}\)

\(\mathrm{H}_{2} \mathrm{NO}_{3}^{+} \rightarrow \mathrm{NO}_{2}^{+}+\mathrm{H}_{2} \mathrm{O}\)

Electricity is conducted through an electrolytic solution due to the movement of ions called electrolytic conduction.

Electrical conductance depends upon-

• Nature of electrolyte: The conductance of an electrolyte depends upon the number of ions present in the solution. Therefore, the greater the number of ions in the solution, the greater is the conductance.
• Concentration of the solution: The molar conductance of electrolytic solution varies with the concentration of the electrolyte. In general, the molar conductance of an electrolyte increases with decrease in concentration or increase in dilution.
• Temperature: The conductivity of an electrolyte depends upon the temperature. With increase in temperature, the conductivity of an electrolyte increases.
• Valence electrons per atom present in metals describes the electric conductance of it.
• Nature and structure is also a significant factors which influences electrical conductance.

An aqueous solution of hydrochloric acidshows negative deviation from Raoult's law.

Raoult's law states that the vapor pressure of a solvent above a solution is equal to the vapor pressure of the pure solvent at the same temperature scaled by the mole fraction of the solvent present, i.e.,

\(\left[\mathrm{P}_{\text {solution }}=\mathrm{X}_{\text {solvent }} \mathrm{P}_{\text {solvent }}^{\circ}\right]\)

If the attraction between different molecules, for example between \(\mathrm{HCl}\) and \(\mathrm{H}_{2} \mathrm{O}\) molecules, is stronger, the escaping tendency from the solution to the vapour phase will be smaller, then the partial vapour pressure will be smaller than predicted by Raoult's law and the system exhibits a negative deviation.

Benzene reacts with \(\mathrm{CH}_3 \mathrm{COCl}\) in the presence of anhydrous \(\mathrm{AlCl}_3\) to give \(\mathrm{C}_6 \mathrm{H}_5 \mathrm{COCH}_3\).

This reaction is called Friedel-Crafts Acylation reaction.

Alpha hydroxy ketones and Aldehydes give a positive test with Tollens' reagent.

Ketones generally don’t give positive test with Tollen’s reagent, but alpha hydroxyl ketones are an exception. Iodoform test, Ester test, etc., are used for alcohols. The litmus test, Sodium bicarbonate test and Ester test are used for carboxylic acid.

Given:

Weight of solute \(({w})=1 {~g}\)

Weight of solvent \(({W})=75 {~g}\)

Boiling point of solution \(=100.114^{\circ} {C}\)

Boiling point of solvent \(=100^{\circ} {C}\)

Therefore, 

\(\triangle {T}=100.114-100=0.114^{\circ} {C}\)

Molecular weight of solute \(({m})=60.1\)

Boiling point elevation constant \(({K})=?\)

We know that:

\({m}=\frac{1000 \times {K} \times {w}}{\Delta {T} \times {W}}\)

or, \({K}=\frac{{m} \times \Delta {T} \times {W}}{1000 \times {w}}\)

\(=\frac{60.1 \times 0.114 \times 75}{1000 \times 1}\)

\(=\frac{513.8}{1000}\)

\(K=0.513\)

In autocatalysis, a reaction product is itself a catalyst for that reaction leading to positive feedback.

A single chemical reaction is said to have undergone autocatalysis, or be autocatalytic, if one of the reaction products is also a reactant and therefore a catalyst in the same or a coupled reaction. The reaction is called an autocatalytic reaction. A catalyst is a substance that accelerates the rate of a chemical reaction but remains chemically unchanged afterwards.

Carbon tetrachloride rises to the atmosphere and deplete the ozone layer. This depletion of ozone layer increases exposure of UV rays to human being which lead to increase of skin cancer, eye diseases and disorder with disruption of the immune system.

Guanidin is not present in nucleic acid and as cytosine, Adenine, Thymine and Guanine are the four main bases found in nucleic acid. Adenine and Guanine are purines while thymine and cytosine are pyrimidines. They together form triple bonded histones of DNA.

Guanidine is another compound which has a chemical formula HNC.

Rate of reaction depends on temperature, concentration of the reactants and presence of catalyst.

Example:

1. At higher temperature, particles collide more frequently and with greater similarity.

2. \(CH _{4}( g )+2 O _{2}( g ) \longrightarrow CO _{2}( g )+2 H _{2} O\) Faster rate

\(C _{25} H _{52}( g )+38 O _{2} \longrightarrow 25 CO _{2}( g )+26 H _{2} O\) Slow rate

So, reaction depends on nature of reactants.

3. A catalyst is a species that speeds up a chemical reaction with being chemically changed upon completion of reaction.