Why Salt Water Carries a Current but Sugar Water Does Not
Sort substances into strong electrolytes, weak electrolytes and non-electrolytes, connect that to whether they contain ions, molecules or both, learn the exact meanings of electrolysis, anode, cathode, oxidation and reduction, and see how conduction through a solution differs from conduction through a wire.
Why does salt water light a bulb when sugar water cannot?
Set up a simple circuit: a battery, a torch bulb and two metal strips dipped into a beaker. Fill the beaker with common salt solution and the bulb glows brightly. Replace it with sugar solution and the bulb stays dark. Try vinegar and the bulb glows, but only faintly.
All three liquids look almost identical, and all three are mostly water. The difference lies in what the dissolved substance becomes in water.
- Salt separates completely into ions, charged particles that can carry current through the liquid
- Sugar stays as neutral molecules, which carry no charge at all
- The acid in vinegar forms a few ions but leaves most of its molecules unchanged
That single idea — whether a substance supplies ions, and how many — sorts every liquid into three groups: strong electrolytes, weak electrolytes and non-electrolytes. It also explains why a current does more than pass through such a liquid. When the ions reach the metal strips they change chemically, and the substance is broken down. That breakdown by electricity is electrolysis.
Electrolysis is quietly behind a great deal of daily life.
- Chlorine used to disinfect drinking water and caustic soda used in soap-making are produced by it
- Aluminium for foil and cooking vessels is extracted by it
- The shiny coat on a nickel-plated tap is put there by it
Before any of that makes sense, a precise vocabulary is needed — electrolyte, electrode, anode, cathode, anion, cation, oxidation and reduction — and a clear picture of how current through a liquid differs from current through a copper wire.
One warning about the words. In everyday speech people say salt water conducts. In chemistry, the salt is the electrolyte; the water only lets its ions move. Keeping that distinction clear prevents most errors in this chapter.
This page covers the first part of the ICSE Class 10 Chemistry chapter on electrolysis: electrolytes and non-electrolytes, substances made of molecules, ions or both, the key terms of electrolysis, and metallic versus electrolytic conduction.
All three liquids look almost identical, and all three are mostly water. The difference lies in what the dissolved substance becomes in water.
- Salt separates completely into ions, charged particles that can carry current through the liquid
- Sugar stays as neutral molecules, which carry no charge at all
- The acid in vinegar forms a few ions but leaves most of its molecules unchanged
That single idea — whether a substance supplies ions, and how many — sorts every liquid into three groups: strong electrolytes, weak electrolytes and non-electrolytes. It also explains why a current does more than pass through such a liquid. When the ions reach the metal strips they change chemically, and the substance is broken down. That breakdown by electricity is electrolysis.
Electrolysis is quietly behind a great deal of daily life.
- Chlorine used to disinfect drinking water and caustic soda used in soap-making are produced by it
- Aluminium for foil and cooking vessels is extracted by it
- The shiny coat on a nickel-plated tap is put there by it
Before any of that makes sense, a precise vocabulary is needed — electrolyte, electrode, anode, cathode, anion, cation, oxidation and reduction — and a clear picture of how current through a liquid differs from current through a copper wire.
One warning about the words. In everyday speech people say salt water conducts. In chemistry, the salt is the electrolyte; the water only lets its ions move. Keeping that distinction clear prevents most errors in this chapter.
This page covers the first part of the ICSE Class 10 Chemistry chapter on electrolysis: electrolytes and non-electrolytes, substances made of molecules, ions or both, the key terms of electrolysis, and metallic versus electrolytic conduction.
What are electrolytes and non-electrolytes, and how are strong and weak electrolytes told apart?
An electrolyte conducts electricity when molten or dissolved and is decomposed by the current; a strong electrolyte is almost completely ionised, a weak electrolyte only partly, and a non-electrolyte not at all.
Electrolyte. A compound which, in the molten state or in aqueous solution, conducts electricity and undergoes chemical decomposition as the current passes.
Non-electrolyte. A compound which does not conduct electricity in the molten state or in aqueous solution, because it does not form ions.
Strong electrolytes — ionise almost completely, so the solution contains a large number of ions and conducts well:
- Salts: sodium chloride, potassium chloride, copper(II) sulphate
- Strong alkalis: sodium hydroxide, potassium hydroxide
- Strong acids: hydrochloric, nitric and sulphuric acids
- Molten ionic compounds: molten lead bromide, molten sodium chloride
Weak electrolytes — ionise only partially, so few ions are present and conduction is poor:
- Weak acids: acetic acid, carbonic acid, formic acid
- Weak alkali: ammonium hydroxide
Non-electrolytes — form no ions:
- Covalent compounds such as sugar, glucose, alcohol, urea, kerosene and carbon tetrachloride
The equations show the difference.
The double arrow is the mark of a weak electrolyte — most acetic acid molecules remain un-ionised at any moment.
Worked example — the bulb test. Five solutions of similar concentration are tested in a circuit with a bulb.
- Dilute sulphuric acid — bright glow: strong electrolyte, almost fully ionised
- Sodium hydroxide solution — bright glow: strong electrolyte
- Acetic acid solution — dim glow: weak electrolyte, only partly ionised
- Ammonium hydroxide solution — dim glow: weak electrolyte
- Glucose solution — no glow: non-electrolyte, molecules only
An everyday example. Electrical appliances carry warnings against handling them with wet hands. Sweat and tap water contain dissolved salts, which are strong electrolytes, so a film of moisture on the skin conducts far better than dry skin.
Two boundary cases worth stating.
- Solid sodium chloride does not conduct, yet it is an electrolyte. The definition refers to the molten or dissolved state, where its ions are free to move
- Pure distilled water conducts so poorly that it is usually treated as a non-electrolyte for practical purposes, although it ionises very slightly. That is why a little acid is added before water is electrolysed — the subject of Part 2
The link to the acids chapter. Strong and weak here mean the same as for acids and bases: they describe how completely a substance ionises, not how concentrated its solution is.
Electrolyte. A compound which, in the molten state or in aqueous solution, conducts electricity and undergoes chemical decomposition as the current passes.
Non-electrolyte. A compound which does not conduct electricity in the molten state or in aqueous solution, because it does not form ions.
Strong electrolytes — ionise almost completely, so the solution contains a large number of ions and conducts well:
- Salts: sodium chloride, potassium chloride, copper(II) sulphate
- Strong alkalis: sodium hydroxide, potassium hydroxide
- Strong acids: hydrochloric, nitric and sulphuric acids
- Molten ionic compounds: molten lead bromide, molten sodium chloride
Weak electrolytes — ionise only partially, so few ions are present and conduction is poor:
- Weak acids: acetic acid, carbonic acid, formic acid
- Weak alkali: ammonium hydroxide
Non-electrolytes — form no ions:
- Covalent compounds such as sugar, glucose, alcohol, urea, kerosene and carbon tetrachloride
The equations show the difference.
The double arrow is the mark of a weak electrolyte — most acetic acid molecules remain un-ionised at any moment.
Worked example — the bulb test. Five solutions of similar concentration are tested in a circuit with a bulb.
- Dilute sulphuric acid — bright glow: strong electrolyte, almost fully ionised
- Sodium hydroxide solution — bright glow: strong electrolyte
- Acetic acid solution — dim glow: weak electrolyte, only partly ionised
- Ammonium hydroxide solution — dim glow: weak electrolyte
- Glucose solution — no glow: non-electrolyte, molecules only
An everyday example. Electrical appliances carry warnings against handling them with wet hands. Sweat and tap water contain dissolved salts, which are strong electrolytes, so a film of moisture on the skin conducts far better than dry skin.
Two boundary cases worth stating.
- Solid sodium chloride does not conduct, yet it is an electrolyte. The definition refers to the molten or dissolved state, where its ions are free to move
- Pure distilled water conducts so poorly that it is usually treated as a non-electrolyte for practical purposes, although it ionises very slightly. That is why a little acid is added before water is electrolysed — the subject of Part 2
The link to the acids chapter. Strong and weak here mean the same as for acids and bases: they describe how completely a substance ionises, not how concentrated its solution is.
Which substances contain only molecules, only ions, or both, and how does that decide conduction?
Non-electrolytes contain only molecules, strong electrolytes in the molten or dissolved state contain only ions of the dissolved substance, and weak electrolytes contain both molecules and ions.
1. Molecules only — non-electrolytes.
- Examples: alcohol, glucose, sugar, kerosene, carbon tetrachloride, and dry liquid hydrogen chloride
- Particles: neutral molecules, no ions
- Conduction: none
2. Ions only — strong electrolytes.
- Examples: molten sodium chloride, sodium chloride solution, potassium hydroxide solution, dilute hydrochloric acid
- Particles: the dissolved substance is present entirely as ions
- Conduction: good
3. Both molecules and ions — weak electrolytes.
- Examples: acetic acid solution, carbonic acid, ammonium hydroxide solution
- Particles: mostly un-ionised molecules, with a small number of ions
- Conduction: poor
A note on what is being counted. Every aqueous solution also contains water molecules. The classification counts the particles of the dissolved substance, so sodium chloride solution is described as containing ions only even though water molecules surround them.
The relation in one line:
Worked example — classify each substance and predict its conduction.
- Molten lead bromide — ions only, and : conducts well
- Kerosene — molecules only: does not conduct
- Vinegar — acetic acid molecules and a few ions: conducts poorly
- Glucose solution — molecules only: does not conduct
- Potassium chloride solution — ions only: conducts well
- Ammonium hydroxide solution — molecules and ions: conducts poorly
The boundary case that shows the idea most clearly — hydrogen chloride.
- Dry hydrogen chloride gas or liquid consists of HCl molecules only, and does not conduct
- Dissolved in water, it ionises almost completely:
- So hydrochloric acid contains ions only and is a strong electrolyte
The same compound moves from one category to another depending on whether water is present — which is exactly why the definition of an electrolyte mentions the aqueous or molten state.
An everyday example. The acid inside a vehicle battery is sulphuric acid, a strong electrolyte chosen because its many ions let a large current flow. Vinegar, a weak electrolyte, could never do that job even at the same concentration, because most of its acid stays as molecules.
Why the number of ions controls conduction. Current through a liquid is carried by moving ions. More ions per unit volume means more charge carried per second, which is why a strong electrolyte lights the bulb brightly and a weak one only dimly, and why a non-electrolyte, with no carriers at all, leaves it dark.
1. Molecules only — non-electrolytes.
- Examples: alcohol, glucose, sugar, kerosene, carbon tetrachloride, and dry liquid hydrogen chloride
- Particles: neutral molecules, no ions
- Conduction: none
2. Ions only — strong electrolytes.
- Examples: molten sodium chloride, sodium chloride solution, potassium hydroxide solution, dilute hydrochloric acid
- Particles: the dissolved substance is present entirely as ions
- Conduction: good
3. Both molecules and ions — weak electrolytes.
- Examples: acetic acid solution, carbonic acid, ammonium hydroxide solution
- Particles: mostly un-ionised molecules, with a small number of ions
- Conduction: poor
A note on what is being counted. Every aqueous solution also contains water molecules. The classification counts the particles of the dissolved substance, so sodium chloride solution is described as containing ions only even though water molecules surround them.
The relation in one line:
Worked example — classify each substance and predict its conduction.
- Molten lead bromide — ions only, and : conducts well
- Kerosene — molecules only: does not conduct
- Vinegar — acetic acid molecules and a few ions: conducts poorly
- Glucose solution — molecules only: does not conduct
- Potassium chloride solution — ions only: conducts well
- Ammonium hydroxide solution — molecules and ions: conducts poorly
The boundary case that shows the idea most clearly — hydrogen chloride.
- Dry hydrogen chloride gas or liquid consists of HCl molecules only, and does not conduct
- Dissolved in water, it ionises almost completely:
- So hydrochloric acid contains ions only and is a strong electrolyte
The same compound moves from one category to another depending on whether water is present — which is exactly why the definition of an electrolyte mentions the aqueous or molten state.
An everyday example. The acid inside a vehicle battery is sulphuric acid, a strong electrolyte chosen because its many ions let a large current flow. Vinegar, a weak electrolyte, could never do that job even at the same concentration, because most of its acid stays as molecules.
Why the number of ions controls conduction. Current through a liquid is carried by moving ions. More ions per unit volume means more charge carried per second, which is why a strong electrolyte lights the bulb brightly and a weak one only dimly, and why a non-electrolyte, with no carriers at all, leaves it dark.
What do electrolysis, electrode, anode, cathode, anion, cation, oxidation and reduction mean?
Electrolysis is the decomposition of an electrolyte by a current; the current enters and leaves through electrodes; cations move to the cathode and gain electrons, which is reduction; anions move to the anode and lose electrons, which is oxidation.
The definitions:
- Electrolysis — the process of decomposition of a chemical compound in the molten or aqueous state by the passage of an electric current, with the ions being discharged as neutral atoms or molecules at the electrodes
- Electrolyte — the compound that conducts and is decomposed
- Electrodes — the conductors, usually metal plates or graphite rods, through which current enters and leaves the electrolyte
- Anode — the electrode connected to the positive terminal of the battery
- Cathode — the electrode connected to the negative terminal
- Anion — a negatively charged ion, attracted to the anode: , , ,
- Cation — a positively charged ion, attracted to the cathode: , , ,
- Oxidation — the loss of electrons by an atom or ion
- Reduction — the gain of electrons by an atom or ion
Examples of oxidation and reduction written as electron changes:
Where each process happens in electrolysis.
- At the cathode, cations gain electrons from the electrode: reduction
- At the anode, anions lose electrons to the electrode: oxidation
A memory aid: the words anode and oxidation both begin with vowels; cathode and reduction both begin with consonants.
Worked example — molten sodium chloride.
- Cathode: — sodium ions gain electrons: reduction
- Anode: — chloride ions lose electrons: oxidation
Check the electrons. For every two electrons given up at the anode, two sodium ions take two electrons at the cathode. Oxidation and reduction always happen together, and the electrons lost at one electrode equal those gained at the other.
An everyday example. Chlorine for disinfecting drinking water is produced at the anode of industrial electrolysis cells, where chloride ions are oxidised. The name of the electrode tells you straight away that the product was made by losing electrons.
The boundary case for later study. In an electrolytic cell the anode is positive. In a battery, which produces electricity instead of consuming it, the anode is the negative terminal. What never changes is that oxidation happens at the anode — the definition is fixed by the process, not by the sign.
A second trap. An anion is attracted to the anode, not named after it by coincidence. Negative ions go to the positive electrode; students who reverse the pairing reverse every electrode equation that follows.
The definitions:
- Electrolysis — the process of decomposition of a chemical compound in the molten or aqueous state by the passage of an electric current, with the ions being discharged as neutral atoms or molecules at the electrodes
- Electrolyte — the compound that conducts and is decomposed
- Electrodes — the conductors, usually metal plates or graphite rods, through which current enters and leaves the electrolyte
- Anode — the electrode connected to the positive terminal of the battery
- Cathode — the electrode connected to the negative terminal
- Anion — a negatively charged ion, attracted to the anode: , , ,
- Cation — a positively charged ion, attracted to the cathode: , , ,
- Oxidation — the loss of electrons by an atom or ion
- Reduction — the gain of electrons by an atom or ion
Examples of oxidation and reduction written as electron changes:
Where each process happens in electrolysis.
- At the cathode, cations gain electrons from the electrode: reduction
- At the anode, anions lose electrons to the electrode: oxidation
A memory aid: the words anode and oxidation both begin with vowels; cathode and reduction both begin with consonants.
Worked example — molten sodium chloride.
- Cathode: — sodium ions gain electrons: reduction
- Anode: — chloride ions lose electrons: oxidation
Check the electrons. For every two electrons given up at the anode, two sodium ions take two electrons at the cathode. Oxidation and reduction always happen together, and the electrons lost at one electrode equal those gained at the other.
An everyday example. Chlorine for disinfecting drinking water is produced at the anode of industrial electrolysis cells, where chloride ions are oxidised. The name of the electrode tells you straight away that the product was made by losing electrons.
The boundary case for later study. In an electrolytic cell the anode is positive. In a battery, which produces electricity instead of consuming it, the anode is the negative terminal. What never changes is that oxidation happens at the anode — the definition is fixed by the process, not by the sign.
A second trap. An anion is attracted to the anode, not named after it by coincidence. Negative ions go to the positive electrode; students who reverse the pairing reverse every electrode equation that follows.
How is metallic conduction different from electrolytic conduction?
In metallic conduction electrons flow through a metal without changing it; in electrolytic conduction ions move through a molten or dissolved electrolyte, which is decomposed at the electrodes.
1. Charge carriers.
- Metallic: free electrons
- Electrolytic: ions — cations moving one way, anions the other
2. Chemical change.
- Metallic: no chemical change in the conductor
- Electrolytic: the electrolyte is decomposed and new substances appear at the electrodes
3. Movement of matter.
- Metallic: no transfer of matter — only electrons drift
- Electrolytic: matter moves, as ions travel to the electrodes and are discharged there
4. State of the conductor.
- Metallic: in the solid and molten state
- Electrolytic: only in the molten or aqueous state, never as a solid
5. Effect of temperature.
- Metallic: conduction decreases as temperature rises, because the vibrating atoms obstruct the electrons more
- Electrolytic: conduction increases as temperature rises, because ions move more freely and weak electrolytes ionise more
Worked comparison — the same current, two conductors. A current passes for an hour through a copper wire and then through copper sulphate solution between two electrodes.
- The copper wire is exactly as it was: same mass, same composition
- The copper sulphate solution has changed: copper has been deposited on the cathode and a product has formed at the anode
A current has flowed through both, but only one has undergone a chemical reaction.
Every electrolysis circuit uses both kinds. Electrons travel through the connecting wires and the electrodes; ions carry the current through the electrolyte; and at the surface of each electrode the two kinds of carrier hand over to one another as ions gain or lose electrons.
An everyday example. The copper wiring in a house can carry current for decades without being used up. A torch battery is different — the chemicals inside react as current flows and eventually run out, because the current inside the battery depends on ions and chemical change.
Two boundary cases.
- Graphite is a non-metal but conducts by electrons, so it shows metallic conduction, which is why graphite rods make good inert electrodes
- Mercury is a liquid but conducts by electrons, so being a liquid does not make a conductor electrolytic — the carrier decides, not the state
1. Charge carriers.
- Metallic: free electrons
- Electrolytic: ions — cations moving one way, anions the other
2. Chemical change.
- Metallic: no chemical change in the conductor
- Electrolytic: the electrolyte is decomposed and new substances appear at the electrodes
3. Movement of matter.
- Metallic: no transfer of matter — only electrons drift
- Electrolytic: matter moves, as ions travel to the electrodes and are discharged there
4. State of the conductor.
- Metallic: in the solid and molten state
- Electrolytic: only in the molten or aqueous state, never as a solid
5. Effect of temperature.
- Metallic: conduction decreases as temperature rises, because the vibrating atoms obstruct the electrons more
- Electrolytic: conduction increases as temperature rises, because ions move more freely and weak electrolytes ionise more
Worked comparison — the same current, two conductors. A current passes for an hour through a copper wire and then through copper sulphate solution between two electrodes.
- The copper wire is exactly as it was: same mass, same composition
- The copper sulphate solution has changed: copper has been deposited on the cathode and a product has formed at the anode
A current has flowed through both, but only one has undergone a chemical reaction.
Every electrolysis circuit uses both kinds. Electrons travel through the connecting wires and the electrodes; ions carry the current through the electrolyte; and at the surface of each electrode the two kinds of carrier hand over to one another as ions gain or lose electrons.
An everyday example. The copper wiring in a house can carry current for decades without being used up. A torch battery is different — the chemicals inside react as current flows and eventually run out, because the current inside the battery depends on ions and chemical change.
Two boundary cases.
- Graphite is a non-metal but conducts by electrons, so it shows metallic conduction, which is why graphite rods make good inert electrodes
- Mercury is a liquid but conducts by electrons, so being a liquid does not make a conductor electrolytic — the carrier decides, not the state
Exam tip
What wins marks on electrolyte classification and definitions?
Give the reason with every classification — ions or molecules, complete or partial ionisation — and write each definition with its exact qualifying words.
- Include molten or aqueous state in the definition of an electrolyte
- Include decomposition — conduction alone does not make a substance an electrolyte
- Classify with a reason: strong electrolyte because it ionises almost completely
- Use a double arrow for weak electrolytes such as acetic acid and ammonium hydroxide
- State the particles present: ions only, molecules only, or both
- Define anode and cathode by the battery terminal they are connected to
- Define oxidation and reduction by electrons, not by oxygen or hydrogen
- Say where each happens: oxidation at the anode, reduction at the cathode
- List at least three differences when comparing metallic and electrolytic conduction, including chemical change and the effect of temperature
- Treat hydrogen chloride carefully — molecules only when dry, ions only in water
The misconception to name. A metal wire is not an electrolyte, even though it conducts. An electrolyte must be decomposed by the current it carries, and a copper wire is unchanged however long the current flows. Using the word electrolyte for any conductor loses the definition mark.
A second trap. Describing a weak electrolyte as a dilute solution. Weak refers to partial ionisation; concentrated acetic acid is still a weak electrolyte, and very dilute hydrochloric acid is still a strong one.
- Include molten or aqueous state in the definition of an electrolyte
- Include decomposition — conduction alone does not make a substance an electrolyte
- Classify with a reason: strong electrolyte because it ionises almost completely
- Use a double arrow for weak electrolytes such as acetic acid and ammonium hydroxide
- State the particles present: ions only, molecules only, or both
- Define anode and cathode by the battery terminal they are connected to
- Define oxidation and reduction by electrons, not by oxygen or hydrogen
- Say where each happens: oxidation at the anode, reduction at the cathode
- List at least three differences when comparing metallic and electrolytic conduction, including chemical change and the effect of temperature
- Treat hydrogen chloride carefully — molecules only when dry, ions only in water
The misconception to name. A metal wire is not an electrolyte, even though it conducts. An electrolyte must be decomposed by the current it carries, and a copper wire is unchanged however long the current flows. Using the word electrolyte for any conductor loses the definition mark.
A second trap. Describing a weak electrolyte as a dilute solution. Weak refers to partial ionisation; concentrated acetic acid is still a weak electrolyte, and very dilute hydrochloric acid is still a strong one.
Did you know
Why is pure water a poor conductor while tap water can give a shock?
Every safety notice warns that water and electricity are a dangerous mix. Yet carefully distilled water is such a poor conductor that it barely lets a torch bulb glimmer. Both statements are true, and the difference is what is dissolved in the water.
Pure water is almost entirely molecules. A tiny fraction of its molecules ionise:
but so few ions form that there is almost nothing to carry a current. On its own, pure water behaves very nearly as a non-electrolyte.
Tap water is a different liquid. On its way through soil and rock it dissolves small amounts of salts — compounds of calcium, magnesium and sodium, among others. Those salts are strong electrolytes, and even small amounts supply plenty of ions. Rainwater collected on a roof, well water and bath water all carry dissolved substances, and so they all conduct well enough to be dangerous.
Your own body adds to the risk. Sweat contains dissolved salts, and the fluids inside the body are solutions of electrolytes. Wet skin loses much of its protective resistance, which is why an appliance touched with wet hands is so much more dangerous than the same appliance touched with dry ones.
The same chemistry explains a laboratory practice. When water is to be split into hydrogen and oxygen by electrolysis, a few drops of dilute sulphuric acid are added first. The acid is a strong electrolyte that supplies ions, so current can flow; without it, pure water would pass almost no current and hardly any gas would form.
And it explains why electrolytes matter in medicine and sport. A salt-and-sugar rehydration drink replaces the dissolved salts lost through sweating and illness. Those salts are literally electrolytes — the same word, used for the same reason, because the body's nerves and muscles depend on the movement of their ions.
Pure water is almost entirely molecules. A tiny fraction of its molecules ionise:
but so few ions form that there is almost nothing to carry a current. On its own, pure water behaves very nearly as a non-electrolyte.
Tap water is a different liquid. On its way through soil and rock it dissolves small amounts of salts — compounds of calcium, magnesium and sodium, among others. Those salts are strong electrolytes, and even small amounts supply plenty of ions. Rainwater collected on a roof, well water and bath water all carry dissolved substances, and so they all conduct well enough to be dangerous.
Your own body adds to the risk. Sweat contains dissolved salts, and the fluids inside the body are solutions of electrolytes. Wet skin loses much of its protective resistance, which is why an appliance touched with wet hands is so much more dangerous than the same appliance touched with dry ones.
The same chemistry explains a laboratory practice. When water is to be split into hydrogen and oxygen by electrolysis, a few drops of dilute sulphuric acid are added first. The acid is a strong electrolyte that supplies ions, so current can flow; without it, pure water would pass almost no current and hardly any gas would form.
And it explains why electrolytes matter in medicine and sport. A salt-and-sugar rehydration drink replaces the dissolved salts lost through sweating and illness. Those salts are literally electrolytes — the same word, used for the same reason, because the body's nerves and muscles depend on the movement of their ions.
Exam relevance
How does electrolyte behaviour lead into JEE and NEET electrochemistry?
This is foundation work for Class 12 Electrochemistry, Class 11 Redox Reactions and Class 11 Equilibrium, all examined in both JEE Main and NEET Chemistry.
Where strong and weak electrolytes lead. Class 12 Electrochemistry measures conduction in solution as conductivity and molar conductivity, and shows that the two kinds of electrolyte behave differently on dilution. Molar conductivity of a strong electrolyte rises only gently as the solution is diluted, while that of a weak electrolyte rises steeply, because dilution ionises more of it. Kohlrausch's law of independent migration of ions is then used to find the limiting molar conductivity of weak electrolytes. Graph-based and numerical questions on these ideas appear in both exams.
Where partial ionisation leads. Class 11 Equilibrium turns ionises partially into the degree of ionisation and the ionisation constant, connecting this lesson's weak electrolytes to pH calculations for weak acids and bases.
Where oxidation and reduction lead. Class 11 Redox Reactions extends the electron-transfer definitions on this page with oxidation numbers, used to balance redox equations and to identify oxidising and reducing agents. Recognising oxidation as loss of electrons and reduction as gain is the starting point for every redox question.
Where the electrode names lead. Class 12 compares electrolytic cells, which consume electrical energy, with galvanic cells, which produce it. The anode is the site of oxidation in both, but it is positive in an electrolytic cell and negative in a galvanic cell — a distinction tested repeatedly, often as an assertion-reason item.
Question types to expect. At this level: definitions, classification with reasons, and comparisons. In competitive papers: conductivity and molar conductivity graphs, Kohlrausch's law numericals, degree of ionisation, redox balancing and cell sign conventions.
The single trap that costs marks. Fixing the anode as the positive electrode in every situation. The sign depends on the type of cell; the process — oxidation — does not, and questions on galvanic cells are designed to catch the candidate who learned only the electrolysis sign.
A second trap. Assuming conductivity and molar conductivity change the same way on dilution. Conductivity falls as a solution is diluted, because there are fewer ions per unit volume, while molar conductivity rises — two quantities that move in opposite directions for a clear reason.
Board versus competitive emphasis. The ICSE paper marks precise definitions, reasoned classification and a list of differences; a competitive paper marks a graph interpretation, a calculated conductivity or a sign convention. The transferable habit is asking what carries the charge and how many carriers there are — the question behind every conductivity result in Class 12.
Where strong and weak electrolytes lead. Class 12 Electrochemistry measures conduction in solution as conductivity and molar conductivity, and shows that the two kinds of electrolyte behave differently on dilution. Molar conductivity of a strong electrolyte rises only gently as the solution is diluted, while that of a weak electrolyte rises steeply, because dilution ionises more of it. Kohlrausch's law of independent migration of ions is then used to find the limiting molar conductivity of weak electrolytes. Graph-based and numerical questions on these ideas appear in both exams.
Where partial ionisation leads. Class 11 Equilibrium turns ionises partially into the degree of ionisation and the ionisation constant, connecting this lesson's weak electrolytes to pH calculations for weak acids and bases.
Where oxidation and reduction lead. Class 11 Redox Reactions extends the electron-transfer definitions on this page with oxidation numbers, used to balance redox equations and to identify oxidising and reducing agents. Recognising oxidation as loss of electrons and reduction as gain is the starting point for every redox question.
Where the electrode names lead. Class 12 compares electrolytic cells, which consume electrical energy, with galvanic cells, which produce it. The anode is the site of oxidation in both, but it is positive in an electrolytic cell and negative in a galvanic cell — a distinction tested repeatedly, often as an assertion-reason item.
Question types to expect. At this level: definitions, classification with reasons, and comparisons. In competitive papers: conductivity and molar conductivity graphs, Kohlrausch's law numericals, degree of ionisation, redox balancing and cell sign conventions.
The single trap that costs marks. Fixing the anode as the positive electrode in every situation. The sign depends on the type of cell; the process — oxidation — does not, and questions on galvanic cells are designed to catch the candidate who learned only the electrolysis sign.
A second trap. Assuming conductivity and molar conductivity change the same way on dilution. Conductivity falls as a solution is diluted, because there are fewer ions per unit volume, while molar conductivity rises — two quantities that move in opposite directions for a clear reason.
Board versus competitive emphasis. The ICSE paper marks precise definitions, reasoned classification and a list of differences; a competitive paper marks a graph interpretation, a calculated conductivity or a sign convention. The transferable habit is asking what carries the charge and how many carriers there are — the question behind every conductivity result in Class 12.
Key takeaways
What must you be able to do from this part?
Three classes of substance, three kinds of particle content, nine definitions and one comparison.
- An electrolyte conducts in the molten or aqueous state and is decomposed by the current; a non-electrolyte does not conduct in either state
- Strong electrolytes ionise almost completely: salts such as NaCl and CuSO4, strong alkalis such as NaOH and KOH, strong acids such as HCl, HNO3 and H2SO4
- Weak electrolytes ionise partly: acetic acid, carbonic acid, ammonium hydroxide — written with a double arrow
- Non-electrolytes form no ions: sugar, glucose, alcohol, kerosene, carbon tetrachloride
- Solid NaCl is an electrolyte that does not conduct until molten or dissolved
- Pure water ionises so slightly that it is treated as practically non-conducting
- Molecules only means non-electrolyte; ions only means strong electrolyte; molecules and ions means weak electrolyte
- Dry hydrogen chloride has molecules only; hydrochloric acid has ions only
- Electrolysis is decomposition of an electrolyte by current, with ions discharged at the electrodes
- Electrodes carry current into and out of the electrolyte; anode connects to the positive terminal, cathode to the negative
- Anions are negative and go to the anode; cations are positive and go to the cathode
- Oxidation is loss of electrons, at the anode; reduction is gain of electrons, at the cathode
- Molten NaCl: at the cathode, at the anode
- Metallic conduction: electrons, no chemical change, no matter transferred, solid or molten, decreases with temperature
- Electrolytic conduction: ions, chemical decomposition, matter transferred, molten or aqueous only, increases with temperature
- Graphite and mercury conduct by electrons, so they show metallic conduction
The quickest self-test is a list of eight liquids. Write down molten lead bromide, vinegar, kerosene, dilute nitric acid, glucose solution, ammonium hydroxide, sodium hydroxide solution and dry liquid hydrogen chloride, and classify each by its particles and its conduction — then justify the two you hesitated over.
- An electrolyte conducts in the molten or aqueous state and is decomposed by the current; a non-electrolyte does not conduct in either state
- Strong electrolytes ionise almost completely: salts such as NaCl and CuSO4, strong alkalis such as NaOH and KOH, strong acids such as HCl, HNO3 and H2SO4
- Weak electrolytes ionise partly: acetic acid, carbonic acid, ammonium hydroxide — written with a double arrow
- Non-electrolytes form no ions: sugar, glucose, alcohol, kerosene, carbon tetrachloride
- Solid NaCl is an electrolyte that does not conduct until molten or dissolved
- Pure water ionises so slightly that it is treated as practically non-conducting
- Molecules only means non-electrolyte; ions only means strong electrolyte; molecules and ions means weak electrolyte
- Dry hydrogen chloride has molecules only; hydrochloric acid has ions only
- Electrolysis is decomposition of an electrolyte by current, with ions discharged at the electrodes
- Electrodes carry current into and out of the electrolyte; anode connects to the positive terminal, cathode to the negative
- Anions are negative and go to the anode; cations are positive and go to the cathode
- Oxidation is loss of electrons, at the anode; reduction is gain of electrons, at the cathode
- Molten NaCl: at the cathode, at the anode
- Metallic conduction: electrons, no chemical change, no matter transferred, solid or molten, decreases with temperature
- Electrolytic conduction: ions, chemical decomposition, matter transferred, molten or aqueous only, increases with temperature
- Graphite and mercury conduct by electrons, so they show metallic conduction
The quickest self-test is a list of eight liquids. Write down molten lead bromide, vinegar, kerosene, dilute nitric acid, glucose solution, ammonium hydroxide, sodium hydroxide solution and dry liquid hydrogen chloride, and classify each by its particles and its conduction — then justify the two you hesitated over.