Question
What is weak electrolyte? Explain relation between concentration of weak electrolyte and molar conductivity.
✓
Answer
→ "Electrolyte which is incompletely ionized in its aqueous solution are known as weak electrolyte.
→" Weak electrolytes like acetic acid have lower degree of dissociation at higher concentrations and hence for such electrolytes, the change in $\hat{m}_{ m }$ with dilution is due to increase in the degree of dissociation and consequently the number of ions in total volume of solution that contains 1 mol of electrolyte.
→ In such cases $\wedge_{ m }$ increases steeply on dilution especially near lower concentrations. Therefor $\wedge_{ m }^0$ cannot be obtained by extra polation of $\wedge_{ m }^0$ zero concentration.
→ At infinite dilution (i.e. concentration $c \rightarrow$ zero electrolyte dissociates completely $(\alpha=1)$, but such low concentration the conductivity of the solution is so low that it cannot be measured accurately.
→ Therefore, $\wedge_{ m }^0$ for weak electrolytes is obtained by using Kohlrausch law of independent migration of ions.
→ At any concentration c , if a is the degree of dissociation then it can be approximated to the ratio of molar conductivity $\wedge_{ m }$ at the concentration c to limiting molar conductivity, $\wedge_{ m }^0$ Thus we have :
$\begin{aligned} \alpha & =\frac{\Lambda_{ m }}{\Lambda_{ m }^0} \\ k _{ a } & =\frac{ c \alpha^2}{1-\alpha}=\frac{ c \Lambda_{ m }^2}{\Lambda_{ m }^{02}\left(1-\frac{\Lambda_{ m }}{\Lambda_{ m }^0}\right)}=\frac{ c \Lambda_{ m }^2}{\Lambda_{ m }^0 \Lambda_{ m }^0-\Lambda_{ m }}\end{aligned}$
→" Weak electrolytes like acetic acid have lower degree of dissociation at higher concentrations and hence for such electrolytes, the change in $\hat{m}_{ m }$ with dilution is due to increase in the degree of dissociation and consequently the number of ions in total volume of solution that contains 1 mol of electrolyte.
→ In such cases $\wedge_{ m }$ increases steeply on dilution especially near lower concentrations. Therefor $\wedge_{ m }^0$ cannot be obtained by extra polation of $\wedge_{ m }^0$ zero concentration.
→ At infinite dilution (i.e. concentration $c \rightarrow$ zero electrolyte dissociates completely $(\alpha=1)$, but such low concentration the conductivity of the solution is so low that it cannot be measured accurately.
→ Therefore, $\wedge_{ m }^0$ for weak electrolytes is obtained by using Kohlrausch law of independent migration of ions.
→ At any concentration c , if a is the degree of dissociation then it can be approximated to the ratio of molar conductivity $\wedge_{ m }$ at the concentration c to limiting molar conductivity, $\wedge_{ m }^0$ Thus we have :
$\begin{aligned} \alpha & =\frac{\Lambda_{ m }}{\Lambda_{ m }^0} \\ k _{ a } & =\frac{ c \alpha^2}{1-\alpha}=\frac{ c \Lambda_{ m }^2}{\Lambda_{ m }^{02}\left(1-\frac{\Lambda_{ m }}{\Lambda_{ m }^0}\right)}=\frac{ c \Lambda_{ m }^2}{\Lambda_{ m }^0 \Lambda_{ m }^0-\Lambda_{ m }}\end{aligned}$
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.
Explore more
Similar questions
Give reasons for the following:
→- Acetylation of aniline reduces its activation effect.
- $\ce{CH_3NH_2}$ is more basic than $\ce{C_6H_5NH_2}.$
- Although $-\ce{NH_2}$ is $o/p$ directing group, yet aniline on nitration gives a significant amount of $m-$nitroaniline.
Write equations of the following reactions:
- Acetylation of aniline
- Coupling reaction
- Carbyl amine reaction
Write the structures of $A, B$ and $C$ in the following$:$
→- $\text{C}_{6}\text{H}_{5}-\text{CONH}_{2}\xrightarrow{Br_2/aq.KOH}A\xrightarrow[0-5^oC]{NaNO_2+Hcl}B\xrightarrow{KI}C$
- $\text{CH}_{3}-\text{Cl}\xrightarrow{KCN}A\xrightarrow{LiAlH_4}B\xrightarrow[\Delta]{CHCl_3+alc.KOH}C$
- Describe the following giving suitable examples:
- Give a chemical test to distinguish between ethanal and propanal.
- Cannizzaro reaction.
- Aldol condensation.
A solution Ni(NO3)2 is electrolysed between platinum electrodes a current of 5 amperes for 20 minutes. What mass of Ni is deposited at the cathode?
Give reasons for the following:
→- Transition metals form alloys.
- $\ce{Mn_2O_3}$ is basic whereas $\ce{Mn_2O_7}$ is acidic.
- $\ce{Eu^{2+}} $ is a strong reducing agent.
Calculate the charge of one mole of electrons.
Complete the following chemical reaction equations:
$\text{Cr}_2\text{O}^{2-}_7(\text{aq})+\text{Fe}^{2+}(\text{aq})+\text{H}^+(\text{aq})\xrightarrow{\ \ \ \ \ \ \ \ \ }$
→$\text{Cr}_2\text{O}^{2-}_7(\text{aq})+\text{Fe}^{2+}(\text{aq})+\text{H}^+(\text{aq})\xrightarrow{\ \ \ \ \ \ \ \ \ }$
Answer the following questions on the basis of the given plot of potential energy vs reaction coordinate$:$
→- What is the threshold energy for the reaction?
- What is the activation energy for forward reaction?
- What is the activation energy for backward reaction?
- What is enthalpy change for the forward reaction?
Give reasons for the following:
→- Aniline does not undergo Friedal$-$Crafts reaction.
- $(CH_3)_2 NH$ is more basic than $(CH_3)_3 N$ in an aqueous solution.
- Primary amines have higher boiling point than tertiary amines.