Why is DC not used for measuring resistance of ionic solution?
Show Hint
Solution and Explanation
Measuring resistance of electrolytic solutions requires careful consideration of electrode processes.
Step 2: Analysis
When DC (direct current) is passed through an ionic solution, the cations migrate toward the cathode and anions toward the anode. This causes electrolysis -- the ions are discharged at the electrodes, depositing products or releasing gases. The composition of the solution changes continuously, and the current-carrying ability (conductance) changes with time. Additionally, a back EMF develops due to the electrolytic products, making accurate resistance measurement impossible.
Step 3: Conclusion
Therefore, AC (alternating current) at high frequency is used. With AC, the direction of current reverses rapidly, preventing net electrolysis and eliminating concentration polarization.
Final Answer: DC causes electrolysis of the solution (products formed at electrodes change solution composition and create back-EMF), making resistance measurement inaccurate. AC (high frequency) is used instead.
Top CBSE CLASS XII Chemistry Questions
- ${AgNO_3}$ does not decompose where :
- Azeotropic mixture of water and HCl boils at 381.5 K. By distilling the mixture it is possible to obtain
Write IUPAC names of the following compounds and classify them into primary, secondary and tertiary amines.
(i) (CH3 )2CHNH2 (ii) CH3 (CH2 )2NH2 (iii) CH3NHCH(CH3 )2
(iv) (CH3 )3CNH2 (v) C6H5NHCH3 (vi) (CH3CH2 )2NCH3 (vii) m–BrC6H4NH2
Give one chemical test to distinguish between the following pairs of compounds.
(i) Methylamine and dimethylamine
(ii) Secondary and tertiary amines
(iii) Ethylamine and aniline
(iv) Aniline and benzylamine
(v) Aniline and N-methylanilineAccount for the following:
(i) pKb of aniline is more than that of methylamine.
(ii) Ethylamine is soluble in water whereas aniline is not.
(iii) Methylamine in water reacts with ferric chloride to precipitate hydrated ferric oxide.
(iv) Although amino group is o– and p– directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline.
(v) Aniline does not undergo Friedel-Crafts reaction.
(vi) Diazonium salts of aromatic amines are more stable than those of aliphatic amines. (vii) Gabriel phthalimide synthesis is preferred for synthesising primary amines.
Top CBSE CLASS XII Conductance of Electrolytic Solutions Questions
- State Kohlrausch's law of independent migration of ions. With the help of a curve, explain why it is not easy to determine $\mathrm{\Lambda^\circ_m}$ for weak electrolytes by extrapolating the concentration – molar conductivity curve, as it is for strong electrolytes.
- The conductivity of 0·001 M acetic acid is $\mathrm{3.905\times10^{-5}}$ S $\mathrm{cm^{-1}}$. Calculate its molar conductivity and degree of dissociation $\mathrm{(\alpha)}$. [Given : $\mathrm{\lambda^\circ_{CH_3COO^-} = 40.9}$, $\mathrm{\lambda^\circ_{H^+} = 349.6\ S\,cm^2\,mol^{-1}}$]
- State Kohlrausch's law of independent migration of ions. With the help of a curve, explain why it is not easy to determine \(\Lambda_m^\circ\) for weak electrolytes by extrapolating the concentration--molar conductivity curve, as it is for strong electrolytes.
- The conductivity of \(0.001\,M\) solution of acetic acid is \(3.905\times10^{-5}\,S\,cm^{-1}\). Calculate its molar conductivity and degree of dissociation (\(\alpha\)). Given : \[ \lambda^\circ_{H^+}=349.6\,S\,cm^2\,mol^{-1} \] \[ \lambda^\circ_{CH_3COO^-}=40.9\,S\,cm^2\,mol^{-1} \]
- Define limiting molar conductivity.
Top CBSE CLASS XII Questions
- 2, b, c are in A.P. and the range of determinant $\begin{vmatrix}1&1&1\\ 2&b&c\\ 4&b^{2}&c^{2}\end{vmatrix}$ is [2, 16]. Then find range of c is
- A boy of mass 50 kg is standing at one end of a, boat of length 9 m and mass 400 kg. He runs to the other, end. The distance through which the centre of mass of the boat boy system moves is
- A capillary tube of radius r is dipped inside a large vessel of water. The mass of water raised above water level is M. If the radius of capillary is doubled, the mass of water inside capillary will be
- A circular disc is rotating about its own axis. An external opposing torque 0.02 Nm is applied on the disc by which it comes rest in 5 seconds. The initial angular momentum of disc is
- A circular disc is rotating about its own axis at uniform angular velocity \(\omega.\) The disc is subjected to uniform angular retardation by which its angular velocity is decreased to \(\frac {\omega}{2}\) during 120 rotations. The number of rotations further made by it before coming to rest is