Basic Science

Some important short question about electrochemistry

1: In redox reaction the number of electrons lost are equal to the number of electrons gained.
Ans; In redox reaction the number of electrons lost are equal to the number of electrons gained because the two processes (reduction and oxidation) occur simultaneously and in chemical equivalent quantities. Thus the number of electron lost must be equal to the number of electrons gained.
(ii) (a)Na+ ion is oxidizing but Na is reducing agent.
Ans oxidizing agent is that which itself have the tendency of gaining electrons or have the tendency to be reduced. Na+ cannot lose electron but have the tendency to gain electron therefore is oxidizing agent.
Na+ +e- → Na
Similarly Reducing agent is that which itself have the tendency to lose electron or have the tendency to be oxidized. Na has the tendency to lose electron easily and therefore is reducing agent.
Na → Na+ + e-
(iii) (b) the Lead storage battery is rechargeable.
Ans; Lead storage battery consist of secondary cell in which the discharging process can be reversed by applying the external voltage.
If we connect the anode and cathode of the external circuit to the cathode and anode of the discharged cell.the current flow in the reverse direction start and the ionized Pb+2 gain electrons and become reduced as Pb while the at anode the Pb+2 lose electrons and react with water to convert into PbO2 . the reactions during recharging are
At cathode PbSO4 + 2e- → Pb + SO4-2
At anode PbSO4 + 2H2O → PbO2 + 4H+ + SO4-2 + 2e-

(iv) A solution of sugar is non conductor but that of NaCl is good conductor.
Ans; Conductivity through solutionis due to the presence of mobile ions.
Sugar is covalent compound and not ionized when dissolve in water , therefore its aqueous solution is non conductor of electricity.
Table salt or sodium chloride is ionic compound , and when dissolve in water become ionized. Due the presence of these ions i.e. Na+ and Cl- ions the aqueous solution of NaCl is good conductor of electricity.
(V) A dry cell is not connected to an external source of current.
Ans; the dry cell is irreversible cell because the Zn+2 and NH3 produced are consumed in the process and converted into a complex compound of formula [Zn(NH3)]+2. This reaction is irreversible. Therefore we cannot obtain the initial state by applying the external source of current.
(VI) NaCl is non conductor in solid state but is good conductor in molten form.
Ans; the conductivity through solid is due to the presence of free electron which are present in metals. Solid NaCl have fixed ions and is therefore insulator.
In molten NaCl the ions become free and they can move . the conductivity through liquid is due to the presence of mobile ions which are present in molten NaCl. Therefore molten NaCl is good conductor.
VII; During electrolysis of fused NaCl Na metal is collected at cathode and not at anode.
Ans; At cathode reduction occur. Cations are electrons deficient and have the tendeny to be reduced. Na+ ions are cations and they must be moved to cathode, gain electrons and to be reduced.
At cathode; Na+ + e- → Na
VIII; SHE act as anode with Cu electrode but act as cathode when connected to Zn electrode.
Ans; SHE has the tendeny to be oxidized as well as reduced or it may act as cathode or anode depend on the nature or reduction potential of other electrode.
The reduction potential of Cu is greater than H2 , therefore Cu will reduced and will act as cathode while SHE will be anode.
While the reduction potential of Zn is less than H2 and therefore Zn will oxidized and will anode while H2 will reduced and will cathode.
IX; In electroplating the article to be plated is made cathode.
Ans; In electroplating the metal to be plated is converted into positive ions or cations.
These cations move towards cathode and reduced or deposit on the cathode. Therefore the article is made cathode that the cations of the desired metals reduced and deposit on it.

कल की ही बात है कक्षा में घुलनशीलता पढ़ा रहा था बता रहा था कि अपने जैसे ही अपने जैसों में घुलते मिलते है। इसका उदाहरण आम जीवन हम देखते है कि होशियार बच्चों के दोस्त होशियार होते है और नालायकों के दोस्त नालायक़ होते है। पानी और नमक एक जैसे है इसलिए नमक पानी मे घुल मिल जाता है। तेल और पानी एक दूसरे से भिन्न है इसलिए घुलते मिलते नही है। एक विद्यार्थी कहता सर मेरे दोस्त तो होशियार है पर मैं तो..... मैंने बीच मव रोकते हुए कहा बस अब तुम भी होशियार बन जायोगे। पीरियड खत्म होने के बाद आया कहने लगा सर आप जो पढ़ाते है मुझे उसका रोजमर्रा जिंदगी का उदहारण तो दो कल आपने घनत्व करवा दिया आज घुलनशीलता के बारे में बताया तो कोई उदहारण तो दो। बहुत जटिल प्रश्न था। कुछ देर सोचा फिर जो जवाब दिया विद्यार्थी पूरा तृप्त हो कर गया। वही उतर आपके सामने पेश करने जा रहा हूँ।

मैंने उसे कहा यदि एक तरफ पेट्रोल पंप पर आग लग जाये और दुसरी तरफ शराब के फैक्ट्री में आग लग जाये तो आग बुझाने में यही विज्ञान काम आयेगा। हम शराब की फैक्ट्री की आग को पानी से खत्म करेंगे जबकि पेट्रोल की आग को पानी से नही। क्योंकि अल्कोहोल पानी मे घुलनशील है वो पानी मे घुल जाता है। जैसे जैसे हम पानी डालते जाएंगे अल्कोहोल की सांद्रता कम होती जाएगी। जिससे उसका इग्निशन तापमान नही मिलेगा। जबकि पेट्रोल पानी मे घुलनशील नही है वो पानी मे घुलनशील नही होगा। पानी का घनत्व पेट्रोल से ज्यादा है वो पेट्रोल पर तैरता रहेगा। जिससे आग नही बुझेगी जब तक सारा तेल खत्म न हो जाये। मेरा अगला पीरियड था तो मैं वहां से निकलने की जल्दी मे था पर मै उसकी आँखों मे सन्तुष्टि देख पा रहा था।

सुनील अरोड़ा