Electrolytes are based onIonic bondorPolar covalent bondCombined substances.Compounds can be dissociated into free moving ions when dissolved in water or heated.Ionic compoundIt can conduct electricity in aqueous solution or in molten state;someCovalent compoundIt can also conduct electricity in aqueous solution, but it also existssolid electrolyte, whichConductivityoriginatelatticeThe migration of ions in.[2]
Fluorine containing electrolytes also work well at temperatures below 0 ℃.[9]
Strong electrolyte(strong electrolyte)aqueous solutionAlmost completely in the middle or molten stateionizationOf electrolyte, fully ionized, not presentIonization equilibrium。Weak electrolyte(weak electrolyte) is an electrolyte that is not completely ionized in aqueous solution or in molten state.The Conductive Properties of Strong and Weak Electrolytes and thesolubilityirrelevant.[1]
Electrolysis is a process in which the current passes through electrolyte solution or molten electrolyte and causes redox reaction at the anode and cathode.This process is the process of converting electrical energy into chemical energy.The conditions for electrolysis are external power supply, electrolyte solution or molten electrolyte, and closed circuit.[4]
For example, water electrolysiscathodeIt is iron plate,anodeNickel plate,electrolytebysodium hydroxideSolution.When electrified, under the effect of external electric field, the positive and negative ions in the electrolyte migrate to the cathode and anode respectively, and the ions move on the electrode solution interfaceelectrochemical reaction。The oxidation reaction is carried out on the anode and the reduction reaction is carried out on the cathode.[3]Water electrolysis is to decompose water into H under the action of external electric fieldtwo(g) And Otwo（g）。Electrolysis is a very powerful promotionRedox reactionMany difficult oxidation-reduction reactions can be realized by electrolysis.For example, molten fluoride can be oxidized on the anode into simple fluorineLithium saltReduction toLithium metal。Electrolytic industryIt plays an important role in the national economy. Many non-ferrous metals andRare metalsSmelting and refining of metals, preparation of basic chemical products, andelectroplate, electropolishinganodic oxidation And so on are achieved through electrolysis.[5]
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There are many factors determining strong and weak electrolytes.Sometimes a substance is a strong electrolyte in one case and a weak electrolyte in another.From key typeBond energy, solubility, concentration and solvent, etc.[6]
(1) Key type
The degree of ionization varies with the bond type of electrolyte.Known typicalIonic compound, such as strong bases and most salts, which can be completely ionized under the action of polar water molecules, and have strong conductivity, we call thisaqueous solutionThe material that can be completely ionized in is a strong electrolyte.And weakPolar bondOfCovalent compound, such as weak acid, weak base and a few salts, which are only partially ionized in water and have weak conductivity, we call this kind of material which can only be partially ionized in aqueous solution weak electrolyte.Therefore, from the structural point of view, the difference between strong and weak electrolytes is due to the different bond types.However, it is not comprehensive to distinguish strong and weak electrolytes only from bond type strength. Strongly polar covalent compounds also belong to weak electrolytes, such as HF.Therefore, the amount of ions in the solution is also related to other factors.[6]
(2) Bond energy
The same type of covalent compounds have different ionization degrees due to different bond energies.For example, HF, HCl, HBr and HI decrease in turn in terms of their bond energy, and their molecular kernel spacing increases in turn.From the point of view that the bond energy of molecules decreases in turn, HF has the largest bond energy, the strongest molecular bond and the most difficult ionization in aqueous solution.In addition, due to the formation of HF moleculeshydrogen bondAlthough part of HF is ionized under the action of water molecules,dissociationIs HthreeO+And F-However, the dissociated F - quickly combines with HF to form HFtwo-、HtwoFthree-、HthreeFfour-Plasma.In 1 mol/L HF solution, F-Only 1%, HFtwoAccounting for 10%, and most of them are multi molecule polymerized ions: HFtwo-、HtwoFthree-、HthreeFfour-In this way, HF becomes a weak acid, while HCl, HBr and HI are strong acids.From HCl to HI, the nuclear spacing in their molecules increases in turn and the bond energy decreases in turn, so theirIonization degreeGradually increased slightly.However, it is one-sided to distinguish strong and weak electrolytes only from the bond energy. Some polar compounds with large bond energy also belong to strong electrolytes.For example, the bond energy of H-Cl (431.3 kJ/mol) is larger than that of H-S (365.8 kJ/mol)aqueous solutionMedium HCl is higher than HtwoS is easily ionized.[6]
(3) Solubility
The solubility of electrolyte also directly affectselectrolyte solutionThe conductivity of.Some ionic compounds, such as BaSOfour、CaFtwoAlthough they are completely ionized when dissolved in water, their solubility is very small, which makes their conductivity of aqueous solution very weakMelting stateWhen the conductivity is very strong, it is still a strong electrolyte.[6]
(4) Concentration
The ionization degree varies with the concentration of electrolyte solution.The thinner the solution, the greater the ionization degree.Therefore, some people think that hydrochloric acid and sulfuric acid are strong electrolytes only in dilute solutionConcentrated solutionMedium is weak electrolyte.fromVapor pressureIt is known that 0.3% of 10 mol/L hydrochloric acid is a covalent molecule, so HCl in 10 mol/L hydrochloric acid is a weak electrolyte.Generally, when the part of solute in molecular state is less than one thousandth, it can be considered as a strong electrolyte. Of course, there is no strict boundary between "strong" and "weak" here.[6]
(5) Solvent
The nature of the solvent also directly affects the strength of the electrolyte.For ionic compounds, water and otherPolar solventThe main function of C is to weaken the gravitation between the ions in the crystal and make them dissociate.According to Coulomb's law, the attraction between ions is:[6]
Where, k is the constant of electrostatic force, Qone、QtwoIs the electric quantity of ions, r is the distance between ions, and ε is the dielectric constant of the solvent.It can be seen from the above formula that the attraction between ions and the solventDielectric constantInversely.The dielectric constant of water is ε=81, so ionic compounds such as LiCl and KCl are easy to ionize in water, showing strong electrolyte properties.However, the dielectric constants of ethanol and benzene are small (ethanol ε=27, benzene ε=2), and ionic compounds are difficult to ionize in them, showing the nature of weak electrolyte.[6]
Therefore, weak electrolytes and strong electrolytes are not a kind of classification of substances in essence, but because of the difference between electrolytes under different conditions such as solvents, there is no obvious boundary between them.[6]
Electrolytes can conduct electricity in aqueous solution or molten statechemical compound；Non electrolyte cannot conduct electricity in aqueous solution or in molten statechemical compound。Simple substancemixtureNo matter whether it can conduct electricity in aqueous solution or molten state, it is not electrolyte or non electrolyte.For example, all metals are neither electrolytes nor non electrolytes.Because they are not compounds, they do not meet the definition of electrolyte.[2]
1. Ionization (essential difference):Electrolytes are compounds that can be ionized under certain conditions, but non electrolytes cannot be ionized.[2]
2. Common substance category:Electrolytes are generally acids, alkalis, salts, typical metal oxides and some non-metallic hydrides.Non electrolytes are usuallyNonmetallic oxideSome non-metallic hydrides and most organic compounds.[2]
3. Compound category:Electrolytes are ionic compounds and some covalent compounds, while non electrolytes are all covalent compounds.[2]
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The Role of Electrolyte in Human Body and Its Balance Regulation
Electrolytes play an important role in human body.Water and electrolytes are widely distributed inside and outside the cells, participating in many important functions and metabolic activities in the body, and electrolytes play a very important role in maintaining normal life activities.The distribution of electrolytes in human body is as follows: in normal human body, sodium ion accounts for 92% of the total cation in extracellular fluid, and potassium ion accounts forIntracellular fluidAbout 98% of the total cation.The relative balance of sodium and potassium ions maintains the integrity of the function and structure of the whole cell.Disturbance of water and electrolyte metabolism can make all organ systems in the body, especiallycardiovascular systemThe physiological function of the nervous system and the material metabolism of the body have corresponding obstacles, which can often lead to death in serious cases.[1]
The balance of water and electrolyte is regulated by the nervous system and some hormones, and this regulation is mainly achieved through the influence of nerves, especially some hormones, on the water and electrolyte processed by the kidney.[1]
1. Maintain body fluid osmotic pressure and water balance
Sodium ion and chloride ion are the main inorganic salt ions that maintain the osmotic pressure of intracellular fluid.normalHuman cellsThe osmotic pressure of internal and external fluid is basically equal, thus maintaining the dynamic balance of intracellular and extracellular fluid water.[1]
2. Maintain acid-base balance of body fluids
Body fluid electrolyte composition buffer pair regulates acid-base balance.[1]
3. Maintain the irritability of nerves and muscles
Nerve and muscle irritability requires a certain concentration and proportion of electrolyte in body fluid to maintain.When sodium and potassium ions are too low, neuromuscular irritability decreases, and limb weakness or even paralysis may occur;When calcium and magnesium ions are too low, nerves and muscles become more irritable, which can lead to hand and foot twitching.[1]
4. Maintain normal material metabolism of cells
A variety of inorganic ions, as the cofactors of metalloenzymes or metal activating enzymes, regulate material metabolism at the cellular level.[1]
Application of solid electrolyte
Compared with liquid electrolyte, the characteristics of solid electrolyte are that it can have a certain shape and strength, and is determined by the conduction mechanism. Generally, its conduction ion is relatively simple, and its ion conductivity has strong selectivity.Therefore, its application often reflects these characteristics.Applications:[7]
1. For various chemical power sources, such as high energy density batteries, micro power batteries,High-temperature fuel cellEtc;[7]
2. For variousElectrochemical sensor, such as oxygen sensor controlling combustion, for environmental protectionGas sensor, oxygen measuring head for metal smelting, etc;[7]
3. It is used to make various electrochemical devices, such as integrating element, micro coulometer, timing element, memory element, etc;[7]
4. For electrochemical catalysis, such as hydrogenation of hydrocarbons;[7]
5. It is used for material separation and purification, such as purification of metal sodium, separation of oxygen, etc;[7]
6. It is made into an ion selective electrode for physical and chemical research, such as activity measurement, diffusion coefficient measurement, etc;[7]
7. Used as a heating element.[7]
Application of Polymer Electrolyte
1. Flocculant
Polymer electrolyte has flocculation effect and is an effective polymer flocculant. Its charged part can neutralize the charge of colloidal particles, destroy the stability of colloidal particles in water, promote their collision, entangle many small particles together through the long chain bridge of polymer, and aggregate into large particles, thus accelerating the settlement.Its flocculation and sedimentation speed is fast, sludge dewatering efficiency is high, and it has special effect on the treatment of some wastewater.Flocculation capacity of polymer electrolyte, ratioinorganic flocculants For example, alum, ferric chloride, etc. are many times to dozens of times, and have unique properties that many inorganic flocculants do not have.[8]
2. Application in paper industry
With the development of synthetic polymer industry, polymer electrolytes, as papermaking additives, are increasingly widely used in the paper industry and play an important role.For example, seasonal carvingpolyacrylamide, cationic starchPolyethyleneimineCan be used as a dry and wet strengthening agent to improve the dry and wet strength of the paper;Carboxymethyl celluloseCationic starch is a sizing agent for paper surface, and can also increase the retention rate of filler and whitening agent;Cationic polyacrylamideIt can flocculate and settle the suspended fine fibers in the precipitation, and has the function of flocculation and capture, so as to recover the cellulose and filler lost in the drainage water of the paper machine and clear water.[8]
3. Application in petroleum industry
Used asClay stabilizer, polymer of fracturing additives, corrosion inhibitor, etc.[8]
Fluorinated electrolyte
In May 2023,Scientists from Argonne National Laboratory and Lawrence Berkeley National Laboratory of the US Department of Energy have developed a fluoride electrolyte that can work well even at temperatures below 0 ℃.[9]
