ScienceCBSE Class 10 · Carbon and its Compounds

Chemical Properties of Carbon Compounds

Updated 14 October 2026 · Fact-checked

Carbon compounds show four main reactions in Class 10: combustion (burning to carbon dioxide and water with heat and light), oxidation of alcohols to acids by oxidising agents, addition of hydrogen to unsaturated compounds using a nickel or palladium catalyst, and substitution of hydrogen by chlorine in saturated hydrocarbons in sunlight.

Understand Chemical Properties of Carbon Compounds

1. Combustion. Carbon in all its forms burns in oxygen to give carbon dioxide with heat and light, and most carbon compounds do the same. These are oxidation reactions:

$C + O_{2} \to C O_{2}$
$C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O$
$C H_{3} C H_{2} O H + 3 O_{2} \to 2 C O_{2} + 3 H_{2} O$

The flame tells you about the fuel and the air supply. Saturated hydrocarbons generally burn with a clean flame, while unsaturated compounds give a yellow flame with lots of black smoke, leaving soot on a metal plate held above. But even a saturated fuel gives a sooty flame if the air supply is limited, because combustion is incomplete. That is why a gas or kerosene stove has air inlets for a clean blue flame; blackened vessel bottoms mean the air holes are blocked and fuel is being wasted. Coal and petroleum also contain some nitrogen and sulphur, so burning them gives oxides of nitrogen and sulphur, which are major pollutants.

2. Oxidation (other than burning). Warm ethanol gently and add alkaline potassium permanganate drop by drop. At first the purple colour disappears, because the permanganate is used up in oxidising the ethanol to ethanoic acid. Once all the ethanol has reacted, extra permanganate stays purple. Substances that can add oxygen to others are oxidising agents; alkaline potassium permanganate and acidified potassium dichromate oxidise alcohols to carboxylic acids:
$C H_{3} C H_{2} O H alkaline KMnO4 + heat C H_{3} C O O H$
(also written with acidified $K_{2} C r_{2} O_{7}$ over the arrow). This counts as oxidation because the product has gained oxygen (and lost hydrogen).

3. Addition reaction. Unsaturated hydrocarbons add hydrogen in the presence of a catalyst such as nickel or palladium to give saturated hydrocarbons: $C_{2} H_{4} + H_{2} Ni C_{2} H_{6}$ . A catalyst makes a reaction happen or changes its rate without being affected itself. This reaction is used to hydrogenate vegetable oils with nickel. Vegetable oils generally have long unsaturated carbon chains; animal fats have saturated chains. Animal fats generally contain saturated fatty acids, said to be harmful for health, so NCERT suggests choosing oils with unsaturated fatty acids for cooking.

4. Substitution reaction. Saturated hydrocarbons are fairly unreactive and inert to most reagents. But in sunlight chlorine reacts rapidly with them, replacing hydrogen atoms one at a time: $C H_{4} + C l_{2} sunlight C H_{3} C l + H C l$ . One atom takes the place of another, hence 'substitution'. With higher alkanes, several products usually form.

A useful pattern: unsaturated compounds undergo addition, saturated compounds undergo substitution. This also gives a way to tell them apart in practice questions, such as by the sootiness of their flames.

Chemical Properties of Carbon Compounds: formulas and key facts

Combustion of methane: $C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O$; Plus heat and light.
Combustion of ethanol: $C H_{3} C H_{2} O H + 3 O_{2} \to 2 C O_{2} + 3 H_{2} O$; Ethanol burns with a clean flame.
Oxidation of ethanol: $C H_{3} C H_{2} O H alkaline KMnO4 + heat C H_{3} C O O H$; Or acidified potassium dichromate. Both are oxidising agents.
Addition of hydrogen: $C_{2} H_{4} + H_{2} Ni C_{2} H_{6}$; Nickel or palladium catalyst; hydrogenation of oils.
Substitution by chlorine: $C H_{4} + C l_{2} sunlight C H_{3} C l + H C l$; Hydrogens replaced one by one.

How to solve Chemical Properties of Carbon Compounds questions

For questions on reactions of carbon compounds, classify first, then write the equation and condition.

1Read the reagent and condition: oxygen and burning (combustion), $K M n O_{4}$ or $K_{2} C r_{2} O_{7}$ (oxidation), hydrogen with Ni or Pd (addition), chlorine with sunlight (substitution).
2Check whether the starting compound is saturated or unsaturated; addition needs a double or triple bond.
3Write the product: $C O_{2}$ + $H_{2} O$ for combustion; carboxylic acid for oxidation of an alcohol; the saturated compound for addition; a chloro compound + HCl for substitution.
4Balance combustion equations (C first, then H, then O).
5Write the condition over the arrow: catalyst, sunlight, heat, oxidising agent.
6Add the observation if asked: sooty yellow flame, clean blue flame, purple colour fading.

Chemical Properties of Carbon Compounds in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Complete and incomplete combustion

Suppose the bottoms of the cooking vessels in your kitchen have started turning black, and the gas stove flame looks yellowish instead of blue.

Explain what is happening, what the black deposit is, why fuel is being wasted, and what simple step would fix it. Write the balanced equation for complete combustion of methane.

Try it first, then show the solutionSolution

A clean blue flame needs enough oxygen for complete combustion: $C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O$ .
A yellow flame and blackened vessels mean the air supply is limited, so combustion is incomplete.
The black deposit is soot, which is unburnt carbon.
Fuel is wasted because part of it is not fully burnt, so less heat is released for the same amount of gas.
The air holes of the burner are probably blocked; cleaning them restores an oxygen-rich mixture and a blue flame.

Answer: Blocked air holes cause incomplete combustion; the black deposit is soot (carbon) and fuel is wasted. Clean the air holes to get complete combustion, $C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O$ .

Memory hook: Blue flame, full burn; yellow flame, sooty pans and wasted gas.

Tricks to remember Chemical Properties of Carbon Compounds

Short memory aids. Say each one aloud once, then use it on a question the same day.

Unsaturated Add, Saturated Substitute
U-A, S-S: unsaturated compounds Add; Saturated ones Substitute.
Use it when: Choosing the reaction type.
Catalysts for hydrogenation
'Nickel and Palladium Pack the hydrogen in.'
Use it when: Naming the catalyst.
Purple vanishes, then stays
Permanganate decolourises while ethanol remains; once ethanol is used up, purple persists.
Use it when: Explaining Activity 4.5 observations.

Chemical Properties of Carbon Compounds: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Balance the combustion equations · 3 marks · Short answerBoard level

Balance: (a) $C H_{4} + O_{2} \to C O_{2} + H_{2} O$ (b) $C H_{3} C H_{2} O H + O_{2} \to C O_{2} + H_{2} O$ . Why are combustion reactions called oxidation reactions?

Try it first, then show the solutionSolution

(a) $C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O$ . Check: C 1, H 4, O 4 (1 mark).
(b) C: 2, so $2 C O_{2}$ ; H: 6, so $3 H_{2} O$ ; O on the right $4 + 3 = 7$ , left has 1 in ethanol, so $3 O_{2}$ : $C H_{3} C H_{2} O H + 3 O_{2} \to 2 C O_{2} + 3 H_{2} O$ (1 mark).
The fuel gains oxygen (carbon and hydrogen combine with oxygen), which is oxidation (1 mark).

Answer: (a) $C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O$ (b) $C H_{3} C H_{2} O H + 3 O_{2} \to 2 C O_{2} + 3 H_{2} O$ ; oxygen is added to the fuel.

Example 2: Ethanol and permanganate · 3 marks · Short answerHarder board level

3 mL of ethanol is warmed in a water bath and 5% alkaline potassium permanganate is added drop by drop. (a) What do you observe at first and after excess is added? Explain. (b) Name the product and write the reaction. (c) Why is this an oxidation reaction?

Try it first, then show the solutionSolution

(a) At first the purple colour disappears, since permanganate is used up in oxidising ethanol; once all ethanol is oxidised, extra permanganate keeps its purple colour (1 mark).
(b) Ethanoic acid: $C H_{3} C H_{2} O H alkaline KMnO4 + heat C H_{3} C O O H$ (1 mark).
(c) Oxygen is added to ethanol (and hydrogen removed); potassium permanganate acts as the oxidising agent (1 mark).

Answer: (a) Decolourises, then purple persists. (b) Ethanoic acid. (c) Gain of oxygen; $K M n O_{4}$ is the oxidising agent.

Example 3: Hydrogenation of oils · 5 marks · Long answerHarder board level

(a) What is an addition reaction? Give the equation for ethene with hydrogen and name the catalyst. (b) Define a catalyst. (c) How is this reaction used in industry? (d) Why does NCERT advise using oils with unsaturated fatty acids for cooking?

Try it first, then show the solutionSolution

(a) A reaction in which atoms add across a double or triple bond of an unsaturated compound, giving a saturated compound: $C_{2} H_{4} + H_{2} Ni C_{2} H_{6}$ ; nickel or palladium catalyst (2 marks).
(b) A substance that makes a reaction occur or changes its rate without itself being affected (1 mark).
(c) Hydrogenation of vegetable oils with a nickel catalyst, turning unsaturated oils into saturated fats (1 mark).
(d) Saturated fatty acids, found mostly in animal fats, are considered bad for health, so cooking oils rich in unsaturated fatty acids are the better choice (1 mark).

Answer: (a) Addition across a multiple bond; $C_{2} H_{4} + H_{2} \to C_{2} H_{6}$ with Ni. (b) Changes rate, itself unaffected. (c) Hydrogenating vegetable oils. (d) Saturated fats are said to be harmful.

Example 4: Substitution · 3 marks · Short answerHOTS / competency

(a) Saturated hydrocarbons are described as fairly unreactive. Under what condition do they react with chlorine? (b) Write the equation for the first step with methane. (c) If the reaction continues, all four hydrogens can be replaced. Write the formula of the final organic product and the total number of HCl molecules formed per methane molecule.

Try it first, then show the solutionSolution

(a) In the presence of sunlight, chlorine reacts very fast with them (1 mark).
(b) $C H_{4} + C l_{2} sunlight C H_{3} C l + H C l$ (1 mark).
(c) Each step replaces one H by Cl and releases one HCl. After four steps the product is $C C l_{4}$ and 4 HCl molecules form: $C H_{4} + 4 C l_{2} \to C C l_{4} + 4 H C l$ (check: C 1, H 4, Cl 8) (1 mark).

Answer: (a) Sunlight. (b) $C H_{4} + C l_{2} \to C H_{3} C l + H C l$ . (c) $C C l_{4}$ ; 4 HCl.

Example 5: Telling saturated from unsaturated by flame · 3 marks · Short answerHarder board level

A student burns two hydrocarbon gases, X ( $C_{2} H_{6}$ ) and Y ( $C_{2} H_{2}$ ), at separate jets with the same air supply and holds a metal plate above each. (a) Predict the flames and the plates. (b) Explain the difference. (c) Could X ever give a sooty flame? When?

Try it first, then show the solutionSolution

(a) X, saturated ethane: clean flame, little or no soot. Y, unsaturated ethyne: yellow flame with black smoke, sooty deposit on the plate (1 mark).
(b) Saturated hydrocarbons generally burn cleanly; unsaturated compounds burn with a sooty flame as combustion is incomplete (1 mark).
(c) Yes, if the air supply is limited, even a saturated hydrocarbon burns incompletely and gives a sooty flame (1 mark).

Answer: (a) X clean, Y sooty yellow. (b) Saturated vs unsaturated. (c) Yes, with limited air.

Where students lose marks in Chemical Properties of Carbon Compounds

The slips examiners see most often, and what to write instead.

Mistake: Missing the condition over the arrow
Students write substitution or addition without sunlight or a catalyst.
Wrong working
$C H_{4} + C l_{2} \to C H_{3} C l + H C l$ (no condition).
Right working
$C H_{4} + C l_{2} sunlight C H_{3} C l + H C l$
Do this: Sunlight for substitution, Ni/Pd for addition, $K M n O_{4}$ / $K_{2} C r_{2} O_{7}$ for oxidation.
Usually costs: ½ mark.
Mistake: Calling oxidation of ethanol 'combustion'
Both involve oxygen.
Wrong working
Ethanol is burnt with $K M n O_{4}$ to give ethanoic acid.
Right working
Ethanol is oxidised by alkaline $K M n O_{4}$ to ethanoic acid; burning gives $C O_{2}$ and water.
Do this: Combustion ends at $C O_{2}$ + $H_{2} O$ ; controlled oxidation stops at the acid.
Usually costs: 1 mark.
Mistake: Unbalanced combustion equations
Students copy the skeletal NCERT forms without balancing.
Wrong working
Skeletal, not balanced: $C H_{4} + O_{2} \to C O_{2} + H_{2} O$
Right working
$C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O$
Do this: Balance C, then H, then O.
Usually costs: ½ to 1 mark.
Mistake: Addition with saturated compounds
Students apply hydrogenation to any hydrocarbon.
Wrong working
$C_{2} H_{6} + H_{2} \to C_{2} H_{8}$
Right working
Ethane is saturated and does not add hydrogen; ethene does: $C_{2} H_{4} + H_{2} \to C_{2} H_{6}$ .
Do this: Check for a double or triple bond first.
Usually costs: 1 mark.

Exam tips

Name the reaction type and the condition in every answer; they carry separate marks.
For Activity 4.5, describe both stages of the permanganate colour change.
Link flame type to saturation and air supply; give the stove example for 'blocked air holes'.
Write 'oxidising agent' for $K M n O_{4}$ and $K_{2} C r_{2} O_{7}$ and define it as a substance that adds oxygen to others.
Remember the health comment on fats as NCERT states it; do not add claims about specific brands or oils.

Practice questions on Chemical Properties of Carbon Compounds

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The conversion of ethanol to ethanoic acid is an example of:
(a) addition (b) substitution (c) oxidation (d) combustion
Hint
Oxygen is added using $K M n O_{4}$ or $K_{2} C r_{2} O_{7}$ .
Answer
(c) oxidation.
Q2 · 1 mark · Assertion-reasonBoard level
Assertion (A): Unsaturated hydrocarbons undergo addition reactions.
Reason (R): Unsaturated hydrocarbons have double or triple bonds between carbon atoms.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Where do the added atoms go?
Answer
(a). Atoms add across the multiple bond.
Q3 · 3 marks · Short answerHarder board level
Write one equation each for (a) a substitution reaction and (b) an addition reaction, naming the condition in each. (c) Which of the two would happen with $C_{3} H_{6}$ and hydrogen?
Hint
$C_{3} H_{6}$ fits $C_{n} H_{2 n}$ .
Answer
(a) $C H_{4} + C l_{2} sunlight C H_{3} C l + H C l$ . (b) $C_{2} H_{4} + H_{2} Ni C_{2} H_{6}$ . (c) Addition: $C_{3} H_{6}$ is propene (unsaturated), giving propane: $C_{3} H_{6} + H_{2} Ni C_{3} H_{8}$ .
Q4 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
Suppose a food company buys a cheap vegetable oil and passes hydrogen through it at a raised temperature with finely divided nickel. The oil becomes a soft solid fat that does not spoil quickly.
(a) Name the type of reaction. (1 mark)
(b) What is the role of nickel? Is nickel used up? (1 mark)
(c) Explain, in terms of saturation, why the oil turns into a solid fat, and comment on what NCERT says about choosing oils for cooking. (2 marks)
Hint
Vegetable oils have long unsaturated chains; animal fats saturated chains.
Answer
(a) Addition (hydrogenation). (b) Catalyst; it speeds up the reaction without being used up or changed. (c) Hydrogen adds across the double bonds of the unsaturated chains, making them saturated like animal fats, which are solids. Animal fats contain saturated fatty acids said to be harmful for health, so NCERT suggests choosing oils with unsaturated fatty acids for cooking.
Q5 · 3 marks · Short answerHOTS / competency
An organic compound A ( $C_{2} H_{6} O$ ) burns with a clean flame. On heating with alkaline potassium permanganate it gives B ( $C_{2} H_{4} O_{2}$ ), which turns blue litmus red. (a) Identify A and B. (b) Write the equation for the combustion of A. (c) Why does A burn with a clean flame?
Hint
An alcohol is oxidised to a carboxylic acid.
Answer
(a) A is ethanol ( $C H_{3} C H_{2} O H$ ), B is ethanoic acid ( $C H_{3} C O O H$ ). (b) $C H_{3} C H_{2} O H + 3 O_{2} \to 2 C O_{2} + 3 H_{2} O$ . (c) Its carbon chain is saturated, and saturated compounds generally burn with a clean flame.
Q6 · 3 marks · Short answerHarder board level
Burning coal and petroleum adds pollutants to the air. (a) Name two such pollutants and say where they come from. (b) Write the equation for the burning of carbon. (c) Why is complete combustion better than incomplete combustion?
Hint
These fuels contain small amounts of nitrogen and sulphur.
Answer
(a) Oxides of sulphur and oxides of nitrogen, from the sulphur and nitrogen present in coal and petroleum. (b) $C + O_{2} \to C O_{2}$ + heat and light. (c) Complete combustion releases all the fuel's heat with no soot; incomplete combustion wastes fuel and produces soot.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Two oxidising agents used to oxidise alcohols?Show answer
Alkaline potassium permanganate and acidified potassium dichromate.
2.Catalysts for addition of hydrogen?Show answer
Nickel or palladium.
3.Condition for substitution of methane by chlorine?Show answer
Sunlight.
4.Flame of unsaturated hydrocarbons?Show answer
Yellow with black smoke (sooty).
5.What does a catalyst do?Show answer
Makes a reaction occur or changes its rate without being affected itself.
6.Why are vessel bottoms blackened on a stove?Show answer
Air holes are blocked; incomplete combustion deposits soot and wastes fuel.

Chemical Properties of Carbon Compounds: frequently asked questions

What are the four chemical properties of carbon compounds in Class 10?

Combustion, oxidation (for example, ethanol to ethanoic acid), addition of hydrogen to unsaturated compounds, and substitution of hydrogen by chlorine in saturated hydrocarbons.

What is the difference between addition and substitution reactions?

In addition, atoms add across a double or triple bond of an unsaturated compound. In substitution, one atom or group replaces another, as chlorine replaces hydrogen in methane in sunlight.

What is hydrogenation of oil?

Adding hydrogen to unsaturated vegetable oils using a nickel catalyst, which turns them into saturated fats.

Why do unsaturated compounds burn with a sooty flame?

They burn incompletely, leaving unburnt carbon as soot, so the flame is yellow and smoky.

Is burning of ethanol the same as its oxidation by potassium permanganate?

Both are oxidation. Burning is complete oxidation to carbon dioxide and water; potassium permanganate oxidises ethanol only as far as ethanoic acid.