EXERCISE
1.(a) Give only one suitable chemical test to identify the following gases.
(i) Ammonia
(ii) Hydrogen chloride
(iii) Carbon dioxide
(iv) Hydrogen
Ans: (i) Ammonia
Test: Bring a moist red litmus paper near the gas.
Observation: The paper turns blue.
(ii) Hydrogen chloride
Test: Bring a rod dipped in ammonium hydroxide near the gas.
Observation: Dense white fumes of ammonium chloride are formed.
(iii) Carbon dioxide
Test: Bubble the gas through lime water (a solution of calcium hydroxide).
Observation: The clear lime water turns milky.
(iv) Hydrogen
Test: Bring a burning splint to the mouth of the gas-filled test tube.
Observation: The gas burns with a ‘pop’ sound.
(b) Select a basic gas mentioned in Q.1 (a). How is the basic nature suspected?
Ans: The gas from the list that is basic in nature is Ammonia (NH₃).You can tell it’s a base because if you hold a piece of moist red litmus paper in this gas, the paper will slowly change its colour from red to blue. This colour change is a simple and classic way to confirm that a substance is basic.
(c) Select acidic gases from the gases mentioned in Q.1(a). How is the acidic nature suspected?
Ans:(c) The acidic gases from Q.1(a) are:
(ii) Hydrogen chloride (HCl)
(iii) Carbon dioxide (CO₂)
How the acidic nature is suspected:
The acidic nature of these gases is suspected through a simple test using moist blue litmus paper.
When a gas suspected to be acidic is brought into contact with moist blue litmus paper, it turns the paper red. This colour change is a classic indicator of acidity.
For Hydrogen chloride (HCl): The gas dissolves in the moisture on the paper to form hydrochloric acid, which immediately and sharply turns the blue litmus paper red.
For Carbon dioxide (CO₂): The gas dissolves in the water to form a weak acid called carbonic acid (H₂CO₃). This acid then slowly turns the blue litmus paper red.
This common test allows us to quickly identify and suspect the presence of an acidic gas.
(d) The two gases A and B are bleaching agents. A is greenish yellow and bleaches due to its oxidising property, while B bleaches due to its reduction. Identify A and B.
Ans: Based on their described properties:
Gas A is Chlorine (Cl₂).
It is identified by its characteristic greenish-yellow colour.
It acts as a bleaching agent through its strong oxidising property, which permanently destroys colour-bearing organic compounds.
Gas B is Sulphur dioxide (SO₂).
It is a colourless gas.
It bleaches coloured materials by a process of reduction, making the colour temporary. The bleached material often regains its colour upon exposure to air or oxidising agents.
(e)(a) Which gas turns blue cobalt chloride paper light pink?
(b) Give one similarity in test between:
(i) Cl₂ and HCl
(ii) SO₂ and CO₂
Ans:(a) Which gas turns blue cobalt chloride paper light pink?
Water vapour is the gas that turns blue cobalt chloride paper light pink. This colour change is a standard test to confirm the presence of moisture.
(b) Give one similarity in test between:
(i) Cl₂ and HCl
Both chlorine gas (Cl₂) and hydrogen chloride gas (HCl) turn moist blue litmus paper red. This is because they both produce acidic solutions when they dissolve in water; HCl forms hydrochloric acid directly, while Cl₂ reacts with water to form hydrochloric and hypochlorous acids.
(ii) SO₂ and CO₂
Both sulphur dioxide (SO₂) and carbon dioxide (CO₂) turn lime water milky when bubbled through it. This happens because they react with calcium hydroxide in lime water to form insoluble white precipitates (calcium sulphite and calcium carbonate, respectively).
2. Name the gases which:
(a) extinguish a burning wooden splinter.
(b) turn moist red litmus blue.
(c) have no effect on moist litmus.
(d) affect the acidified K₂Cr₂O₇ paper and also turn lime water milky.
Ans: (a) Gases that extinguish a burning wooden splinter:
These are generally non-combustible gases that do not support combustion. Common examples include Carbon dioxide (CO₂), Nitrogen (N₂), and Chlorine (Cl₂).
(b) Gases that turn moist red litmus blue:
This is a characteristic test for basic (alkaline) gases. The most common example is Ammonia (NH₃).
(c) Gases that have no effect on moist litmus:
These are neutral gases.
(d) Gases that affect acidified K₂Cr₂O₇ paper and also turn lime water milky:
The acidified potassium dichromate paper turns from orange to green, indicating a reducing gas. Turning lime water milky shows the gas is carbon dioxide. The only common gas that fits both properties is Sulphur dioxide (SO₂). It reduces the dichromate and, when produced in excess during a reaction, can turn lime water milky before the precipitate dissolves with more gas.
3. Name:
(a) Two carbonates which do not produce carbon dioxide on heating.
(b) A colourless gas which bleaches.
(c) Gases which have a sour taste.
(d) A greenish yellow gas which also bleaches.
(e) A gas with a rotten egg smell.
Ans: (a) Sodium carbonate (Na₂CO₃) and Potassium carbonate (K₂CO₃). These two are very stable and do not break down when heated alone.
(b) A colourless gas which bleaches.
Ans: Sulphur dioxide (SO₂). It acts as a bleaching agent, especially for organic dyes and materials like straw or paper.
(c) Gases which have a sour taste.
Ans: Acidic gases like Carbon dioxide (CO₂) and Sulphur dioxide (SO₂) can produce a sour or sharp taste when dissolved in water, forming carbonic acid and sulphurous acid respectively.
(d) A greenish yellow gas which also bleaches.
Ans: Chlorine (Cl₂). It is a greenish-yellow coloured gas known for its strong bleaching action.
(e) A gas with a rotten egg smell.
Ans: Hydrogen sulphide (H₂S). It is well known for its characteristic foul smell of rotten eggs.
4. From the following list of substances, choose those which meet the description given below:
Substances: Ammonium chloride, ammonium nitrate, chlorine, dilute hydrochloric acid, iron, lead nitrate, manganese (IV) oxide, silver nitrate, sodium nitrate, sodium nitrite, sulphur.
Description: Two compounds whose aqueous solutions give white precipitates with dilute hydrochloric acid.
Ans: The two compounds whose aqueous solutions give white precipitates with dilute hydrochloric acid are Silver nitrate (AgNO₃) and Lead nitrate (Pb(NO₃)₂).
Explanation:
When dilute hydrochloric acid (HCl) is added to their solutions, the following double displacement reactions occur, forming insoluble white precipitates:
With Silver nitrate solution:
AgNO₃ (aq) + HCl (aq) → AgCl (s) ↓ + HNO₃ (aq)
The silver chloride (AgCl) formed is a white precipitate.
With Lead nitrate solution:
Pb(NO₃)₂ (aq) + 2HCl (aq) → PbCl₂ (s) ↓ + 2HNO₃ (aq)
The lead chloride (PbCl₂) formed is also a white precipitate.
5. Name the anion present in each of the following compounds:
(a) Compound A, when warmed with concentrated sulphuric acid, gives a gas which fumes in moist air and gives dense white fumes with ammonia.
(b) When barium chloride solution is added to a solution of compound B, a white precipitate insoluble in dilute hydrochloric acid is formed.
(c) The action of heat on the insoluble compound C produces a gas which turns lime water milky.
(d) Compound D, when warmed with dilute sulphuric acid, gives a gas which turns acidified potassium dichromate solution green.
Ans: (a) Compound A: Chloride ion (Cl⁻)
When warmed with concentrated sulphuric acid, a chloride salt produces hydrogen chloride (HCl) gas. This gas is known to fume in moist air. Furthermore, hydrogen chloride gas reacts with ammonia gas to form a dense white smoke of ammonium chloride (NH₄Cl), which is a characteristic confirmatory test.
(b) Compound B: Sulphate ion (SO₄²⁻)
The sulphate ion reacts with barium ions from barium chloride to form a white precipitate of barium sulphate (BaSO₄). A key identifying feature of this precipitate is that it is insoluble in dilute hydrochloric acid, which helps distinguish it from other white precipitates like those of carbonates or sulphites.
(c) Compound C: Carbonate ion (CO₃²⁻)
Many insoluble carbonates, such as copper carbonate or zinc carbonate, decompose upon heating to release carbon dioxide (CO₂) gas. The standard test for carbon dioxide is that it turns lime water (a solution of calcium hydroxide) milky due to the formation of insoluble calcium carbonate.
(d) Compound D: Sulphite ion (SO₃²⁻)
When a sulphite is warmed with a dilute acid like sulphuric acid, it produces sulphur dioxide (SO₂) gas. Sulphur dioxide is a reducing agent. When this gas is passed through acidified potassium dichromate solution, it reduces the orange dichromate ions to green chromium ions, which is a specific and observable colour change for this test.
6)A given white crystalline salt was tested as follows:
(a) It dissolved in water and the resulting solution turned blue litmus red.
(b) Addition of barium chloride solution to this solution gave a white precipitate.
(c) A flame test on the salt gave a persistent golden-yellow colourisation.
What conclusions can be drawn for each observation?
Ans: a) The solution turns blue litmus red.
This indicates that the aqueous solution of the salt is acidic. This typically happens with salts that are formed from a strong acid and a weak base.
(b) Addition of barium chloride solution gives a white precipitate.
This white precipitate is barium sulphate (BaSO₄), which is insoluble. It forms when the barium ion (Ba²⁺) from barium chloride reacts with the sulphate ion (SO₄²⁻). Therefore, the salt contains the sulphate (SO₄²⁻) anion.
(c) Flame test gives a persistent golden-yellow colour.
A golden-yellow flame is the characteristic test for the sodium (Na⁺) cation.
Final Conclusion:
By combining all these conclusions, the white crystalline salt is identified as Sodium Sulphate (Na₂SO₄). The acidity of its solution can be confirmed by other tests.
7)(a) Sodium hydroxide solution is added to solution A. A white precipitate is formed which is insoluble in excess sodium hydroxide solution. Name the metal ion present in solution A.
(b) When ammonium hydroxide is added to solution B, a pale blue precipitate is formed. This precipitate dissolves in excess ammonium hydroxide giving an inky blue solution. Name the cation present in solution B.
(c) When an ammonium salt is warmed with sodium hydroxide solution, ammonia gas is evolved. State three ways in which you could identify this gas.
Ans:(a) Metal ion in solution A:
The metal ion present in solution A is the Calcium ion (Ca²⁺). This is identified by the formation of a white precipitate of calcium hydroxide [Ca(OH)₂], which is insoluble in an excess of sodium hydroxide solution.
(b) Cation in solution B:
The cation present in solution B is the Copper(II) ion (Cu²⁺). This is confirmed by the initial formation of a pale blue precipitate of copper(II) hydroxide [Cu(OH)₂], which then dissolves in excess ammonium hydroxide to form a soluble, deep inky-blue complex tetraamminecopper(II) ion [Cu(NH₃)₄]²⁺.
(c) Three tests to identify Ammonia gas:
Litmus Paper Test: Bring a moist red litmus paper near the gas. If it is ammonia, the paper will turn blue, confirming its basic nature.
Fuming Test: Bring a glass rod dipped in concentrated hydrochloric acid near the mouth of the test tube. Dense white fumes of ammonium chloride will form if ammonia gas is present.
Alkaline Smell Test: Carefully smell the gas. It has a characteristic pungent (sharp, choking) odour that is easily recognizable.
8.Complete the following table and write your Observations
| Hydrogen Sulphide | Ammonia | Sulphur Dioxide | Hydrogen chloride | |
| Shake the gas with red litmus solution | ||||
| Shake the gas with blue litmus solution | ||||
| Apple a burning splint to the gas |
Ans:
| Hydrogen Sulphide | Ammonia | Sulphur Dioxide | Hydrogen chloride | |
| Shake the gas with red litmus solution | No change.Litmus stays red. | Turns blue It is a basic gas | Turns red | Turns red |
| Shake the gas with blue litmus solution | No change.Litmus stays blue. | No change | Turns red | Turns red |
| Apple a burning splint to the gas | Splint is extinguised | Splint is extinguised | Splint is extinguised | Splint is extinguised |
10. Distinguish by a chemical test:
(a) Sodium carbonate and sodium sulphide
(b) Sodium chloride and sodium sulphide
(c) Sodium hydroxide solution and ammonium hydroxide solution
(d) Ammonium sulphate and sodium sulphate
(e) Sulphuric acid from nitric acid and hydrochloric acid
Ans:(a) Sodium carbonate and sodium sulphide
Add dilute HCl.
Sodium carbonate releases CO₂ gas with brisk effervescence, turning lime water milky.
Sodium sulphide releases H₂S gas with a rotten egg smell, turning lead acetate paper black.
(b) Sodium chloride and sodium sulphide
Add lead nitrate solution.
Sodium sulphide gives a black precipitate of lead sulphide.
(c) Sodium hydroxide and ammonium hydroxide
Warm with an ammonium salt.
Sodium hydroxide shows no change.
Ammonium hydroxide releases ammonia gas, turning red litmus blue.
(d) Ammonium sulphate and sodium sulphate
Warm with NaOH solution.
Ammonium sulphate releases ammonia gas, turning red litmus blue.
Sodium sulphate shows no change.
(e) Sulphuric acid from nitric acid and hydrochloric acid
Add barium chloride solution.
Sulphuric acid gives a white precipitate of barium sulphate, insoluble in acids.
Nitric acid and hydrochloric acid show no precipitate.
12. State your observations when:
(a) Lead nitrate solution and sodium chloride solution are mixed.
(b) Zinc chloride solution, zinc nitrate solution and zinc sulphate solutions are added individually to:
(i) Barium chloride solution
(ii) Lead nitrate solution
(c) Bicarbonates are decomposed by dilute H₂SO₄.
2NaHCO₃ + H₂SO₄ → Na₂SO₄ + 2H₂O + 2CO₂
2KHCO₃ + H₂SO₄ → K₂SO₄ + 2H₂O + 2CO₂
Ans: (a) Lead nitrate and sodium chloride solutions are mixed:
A white precipitate of lead chloride forms.
(b) Zinc chloride, zinc nitrate, and zinc sulphate solutions added to:
(i) Barium chloride solution:
Only zinc sulphate forms a white precipitate of barium sulphate. The others show no change.
(ii) Lead nitrate solution:
Zinc chloride gives a white precipitate of lead chloride.
Zinc sulphate gives a white precipitate of lead sulphate.
Zinc nitrate shows no reaction.
(c) Bicarbonates decomposed by dilute H₂SO₄:
A colorless gas (carbon dioxide) is released with brisk effervescence. The gas turns lime water milky.
13. The questions (i) to (v) refer to the following salt solutions listed A to F.
A. Copper nitrate
B. Iron (II) sulphate
C. Iron (III) chloride
D. Lead nitrate
E. Magnesium sulphate
F. Zinc chloride
(i) Which two solutions will give a white precipitate when treated with dilute hydrochloric acid followed by barium chloride solution?
(ii) Which two solutions will give a white precipitate when treated with dilute nitric acid followed by silver nitrate solution?
(iii) Which solution will give a white precipitate when either dilute hydrochloric acid or dilute sulphuric acid is added to it?
(iv) Which solution becomes a deep/inky blue colour when excess of ammonium hydroxide is added to it?
(v) Which solution gives a white precipitate with excess ammonium hydroxide solution?
Ans:(i) Which two solutions will give a white precipitate when treated with dilute hydrochloric acid followed by barium chloride solution?
Ans: B. Iron (II) sulphate and E. Magnesium sulphate.
Reason: The first step (adding dilute HCl) confirms the absence of carbonate and sulfite ions, which would have produced effervescence. The second step (adding BaCl₂) tests for the sulfate ion (SO₄²⁻). Both FeSO₄ and MgSO₄ contain sulfate ions, which react with BaCl₂ to form a white precipitate of barium sulfate (BaSO₄).
(ii) Which two solutions will give a white precipitate when treated with dilute nitric acid followed by silver nitrate solution?
Ans: A. Copper nitrate and F. Zinc chloride.
Reason: The first step (adding dilute HNO₃) confirms the absence of carbonate ions. The second step (adding AgNO₃) tests for chloride ions (Cl⁻). Both Cu(NO₃)₂ and ZnCl₂ do not contain chloride ions, so this answer seems incorrect. The correct solutions should be those containing chloride ions, which are C. Iron (III) chloride and F. Zinc chloride. They form a white precipitate of silver chloride (AgCl) with silver nitrate.
(iii) Which solution will give a white precipitate when either dilute hydrochloric acid or dilute sulphuric acid is added to it?
Ans: D. Lead nitrate.
Reason: Lead ions (Pb²⁺) form insoluble salts with both chloride and sulfate ions. With HCl, it forms white lead chloride (PbCl₂) precipitate. With H₂SO₄, it forms white lead sulfate (PbSO₄) precipitate.
(iv) Which solution becomes a deep/inky blue colour when excess of ammonium hydroxide is added to it?
Ans: A. Copper nitrate.
Reason: Copper ions (Cu²⁺) first form a pale blue precipitate of copper hydroxide with NH₄OH. This precipitate dissolves in excess NH₄OH to form a deep or inky blue complex ion, [Cu(NH₃)₄]²⁺ (tetraamminecopper(II)).
(v) Which solution gives a white precipitate with excess ammonium hydroxide solution?
Ans: F. Zinc chloride.
Reason: Zinc ions (Zn²⁺) form a white precipitate of zinc hydroxide with NH₄OH. Unlike other metal hydroxides, this white precipitate is soluble in excess NaOH but not in excess NH₄OH, so it persists as a white precipitate.
14. Salts A, B, C, D and E undergo reactions (i) to (v) respectively. Identify the anion present in these salts on the basis of these reactions.
(a) When silver nitrate solution is added to a solution of A, a white precipitate, insoluble in dilute nitric acid, is formed.
(b) Addition of dilute hydrochloric acid to B produces a gas which turns lead acetate paper black.
(c) When a freshly prepared solution of ferrous sulphate is added to a solution of C and concentrated sulphuric acid is gently poured from the side of the test-tube, a brown ring is formed.
(d) When dilute sulphuric acid is added to D, a gas is produced which turns acidified potassium dichromate solution from orange to green.
(e) Addition of dilute hydrochloric acid to E produces an effervescence. The gas produced turns lime water milky but does not affect acidified potassium dichromate solution.
Ans: (a) The white precipitate insoluble in dilute nitric acid indicates the anion is Chloride (Cl⁻).
(b) The gas that turns lead acetate paper black is hydrogen sulfide (H₂S), so the anion is Sulfide (S²⁻).
(c) The formation of a brown ring confirms the anion is Nitrate (NO₃⁻).
(d) The gas that turns acidified potassium dichromate green is sulfur dioxide (SO₂), so the anion is Sulfite (SO₃²⁻).
(e) The effervescence producing a gas that turns lime water milky but does not affect acidified K₂Cr₂O₇ is carbon dioxide (CO₂), indicating the anion is Carbonate (CO₃²⁻).
2008
(a) The salt which in solution gives a pale green precipitate with sodium hydroxide solution and a white precipitate with barium chloride solution is:
(i) Iron (III) sulphate
(ii) Iron (II) sulphate
(iii) Iron (II) chloride
(iv) Iron (III) chloride
Ans:(ii) Iron (II) sulphate
The pale green precipitate with sodium hydroxide is characteristic of ferrous hydroxide, Fe(OH)₂, which confirms the Iron (II) cation.The white precipitate with barium chloride is barium sulphate, BaSO₄, which confirms the sulphate anion.Therefore, the salt is Iron (II) sulphate, FeSO₄.
(b) Identify the following substances:
(i) An alkaline gas A which gives dense white fumes with hydrogen chloride.
(ii) A dilute acid B which does not normally give hydrogen when reacted with metals but does give a gas when it reacts with copper.
(iii) Gas C has an offensive smell like rotten eggs.
(iv) Gas D is a colourless gas which can be used as a bleaching agent.
(v) Liquid E can be dehydrated to produce ethene.
Ans:
(i) A is Ammonia gas (NH₃)
It is the common alkaline gas that creates dense white fumes of ammonium chloride with hydrogen chloride.
(ii) B is Nitric acid (HNO₃)
This dilute acid typically does not produce hydrogen with most metals. However, with copper, it gives nitrogen dioxide gas.
(iii) C is Hydrogen sulphide gas (H₂S)
This gas is well-known for its distinctive, offensive smell similar to rotten eggs.
(iv) D is Sulphur dioxide gas (SO₂)
It is a colourless gas that acts as a bleaching agent in the presence of moisture.
(v) E is Ethanol (C₂H₅OH)
Upon dehydration with concentrated sulphuric acid, ethanol loses a water molecule to form ethene gas.
2009
(a) Carbon dioxide and sulphur dioxide gas can be distinguished by using:
(i) moist blue litmus paper
(ii) lime water
(iii) acidified potassium dichromate paper
(iv) none of the above.
Ans: The correct choice is (iii) acidified potassium dichromate paper.
Reason: Sulphur dioxide (SO₂) gas will turn the acidified potassium dichromate paper from orange to green. Carbon dioxide (CO₂) gas has no effect on this paper, allowing you to tell them apart.
The other options are not suitable because:
(i) moist blue litmus paper: Both gases are acidic and will turn blue litmus red.
(ii) lime water: Both gases will turn lime water milky.
(b) Identify the substance ‘R’ based on the information given below:
The pale green solid ‘R’ turns reddish brown on heating. Its aqueous solution gives a white precipitate with barium chloride solution. The precipitate is insoluble in mineral acids.
Ans: the substance R is Ferrous Sulphate (FeSO₄).
Explanation:
Pale green solid: Ferrous sulphate crystals (FeSO₄·7H₂O) are pale green.
Turns reddish brown on heating: Upon heating, ferrous sulphate decomposes to form ferric oxide (Fe₂O₃), which is reddish-brown in color.
Gives white precipitate with barium chloride: Its aqueous solution contains sulphate ions (SO₄²⁻). These ions react with barium chloride (BaCl₂) to form a white precipitate of barium sulphate (BaSO₄).
Precipitate insoluble in mineral acids: Barium sulphate (BaSO₄) is a highly insoluble salt and does not dissolve in strong acids (mineral acids).
(c) Give one chemical test to distinguish between the following pairs of compounds.
(i) Zinc sulphate soln. and zinc chloride soln.
(ii) Iron (II) chloride soln. and iron (III) chloride soln.
(iii) Calcium nitrate soln. and calcium chloride soln.
Ans:(i) Distinguish between Zinc Sulphate and Zinc Chloride
Test: Add Barium Chloride solution.
Zinc Sulphate: Forms a white precipitate.
Zinc Chloride: No precipitate forms.
(ii) Distinguish between Iron (II) Chloride and Iron (III) Chloride
Test: Add Sodium Hydroxide solution.
Iron (II) Chloride: A dirty green precipitate forms.
Iron (III) Chloride: A reddish-brown precipitate forms.
(iii) Distinguish between Calcium Nitrate and Calcium Chloride
Test: Add Silver Nitrate solution.
Calcium Chloride: A white, curdy precipitate is seen.
Calcium Nitrate: No visible reaction occurs.
2010
(a) Select the correct answer from A, B, C, D and E.
A. Nitroso iron (II) sulphate
B. Iron (III) chloride
C. Chromium sulphate
D. Lead (II) chloride
E. Sodium chloride.
Ans: The compound which is responsible for the green colour formed when SO₂ is bubbled through acidified potassium dichromate solution.
The compound responsible for the green colour is C. Chromium sulphate.
Explanation:
When sulphur dioxide (SO₂) gas is bubbled through acidified potassium dichromate solution, the orange dichromate ions (Cr₂O₇²⁻) are reduced. During this reaction, the chromium changes from its +6 oxidation state (orange) to the +3 oxidation state. Chromium in the +3 state forms green hydrated ions, which is observed as chromium sulphate in solution. Therefore, chromium sulphate is the compound that causes the characteristic green colour.
(b) State your observation:
(i) a piece of moist blue litmus paper.
(ii) paper soaked in potassium permanganate solution – is introduced in each case into a jar of sulphur dioxide.
(c) Write the equation for the reaction of magnesium sulphate solution with barium chloride solution.
Ans: (b) Observations:
(i) The moist blue litmus paper turns red.
(ii) The paper soaked in potassium permanganate solution turns from pink to colourless.
(c) Chemical Equation:
Ans: MgSO₄(aq) + BaCl₂(aq) → BaSO₄(s)↓ + MgCl₂(aq)
(Observation: A white precipitate of Barium Sulphate is formed.)
2011(a) Choose from the list of substances – Acetylene gas, aqua fortis, coke, brass, barium chloride, bronze, platinum.
(Note: The question is incomplete in the provided text.)
Ans:
“Identify the alloys from the given list.”
Answer: From the list, the substances that are alloys are Brass and Bronze. Both are well-known metal mixtures, not pure elements. Brass is mainly copper and zinc, while bronze is primarily copper and tin.
“Which substance is a strong oxidizing acid?”
Answer: The strong acid in the list is Aqua fortis. This is the historical name for nitric acid, which is known for its strong, corrosive properties and is often used in laboratories for various chemical reactions.
“Name a substance used as a laboratory reagent to test for sulfate ions.”
Answer: The substance used for this test is Barium chloride. In the lab, when we add it to a solution containing sulfate ions, it instantly forms a white, insoluble precipitate of barium sulfate, making the test very reliable.
“Which of these is a noble or inert metal?”
Answer: The noble metal in the list is Platinum. It is famous for its high resistance to corrosion and oxidation, which is why it’s often used in jewelry and as a catalyst in many industrial processes.
“Which substance is an unsaturated hydrocarbon gas?”
Answer: The gaseous hydrocarbon is Acetylene gas. It’s a colorless gas widely used as a fuel in welding and metal-cutting torches because it burns with a very hot flame.
“Identify the substance used as a solid fuel.”
Answer: The substance used as a solid fuel is Coke. It is a carbon-rich material produced by heating coal in the absence of air and is primarily used in blast furnaces to smelt iron from its ore.
2012
(a) Name the gas which turns acidified potassium dichromate solution green.
(b) Identify the anion present in the following compounds:
(i) Compound X on heating with copper turnings and conc. sulphuric acid liberates a reddish brown gas.
(ii) When a solution of compound Y is treated with silver nitrate solution a white precipitate is obtained which is soluble in excess of ammonium hydroxide solution.
(iii) Compound Z which on reacting with dilute sulphuric acid liberates a gas which turns lime water milky, but the gas has no effect on acidified potassium dichromate solution.
(iv) Compound L on reacting with barium chloride solution gives a white precipitate insoluble in dilute hydrochloric acid or dilute nitric acid.
(c) State one chemical test between each of the following pairs:
(i) Sodium carbonate and sodium sulphite.
(ii) Ferrous nitrate and lead nitrate.
(iii) Manganese dioxide and copper (II) oxide.
(d) State your observation: A zinc granule is added to copper sulphate solution.
(e) Give a balanced equation for the reaction: Silver nitrate solution and sodium chloride solution.
Ans: (a) Name the gas which turns acidified potassium dichromate solution green.
Ans: Sulphur dioxide gas (SO₂).
(b) Identify the anion present in the following compounds:
(i) Compound X on heating with copper turnings and conc. sulphuric acid liberates a reddish brown gas.
Ans: The reddish-brown gas is nitrogen dioxide (NO₂). The anion present in compound X is the nitrate ion (NO₃⁻).
(ii) When a solution of compound Y is treated with silver nitrate solution a white precipitate is obtained which is soluble in excess of ammonium hydroxide solution.
Ans: The white precipitate soluble in excess NH₄OH indicates the presence of the chloride ion (Cl⁻).
(iii) Compound Z which on reacting with dilute sulphuric acid liberates a gas which turns lime water milky, but the gas has no effect on acidified potassium dichromate solution.
Ans: The gas that turns lime water milky is carbon dioxide (CO₂). Since it does not affect acidified K₂Cr₂O₇, it confirms it is CO₂ and not SO₂. The anion present is the carbonate ion (CO₃²⁻).
(iv) Compound L on reacting with barium chloride solution gives a white precipitate insoluble in dilute hydrochloric acid or dilute nitric acid.
Ans: A white precipitate with BaCl₂ that is insoluble in dilute acids is characteristic of the sulphate ion (SO₄²⁻).
(c) State one chemical test between each of the following pairs:
(i) Sodium carbonate and sodium sulphite.
Ans: Add dilute sulphuric acid to both.
Sodium Carbonate: Will produce carbon dioxide (CO₂) gas which turns lime water milky.
Sodium Sulphite: Will produce sulphur dioxide (SO₂) gas which has a pungent, choking smell and turns acidified potassium dichromate paper from orange to green.
(ii) Ferrous nitrate and lead nitrate.
Ans: Add a few drops of potassium iodide (KI) solution to both.
Lead Nitrate: Will form a bright yellow precipitate of lead iodide (PbI₂).
Ferrous Nitrate: Will not form a precipitate (may show a colour change due to oxidation, but no distinct yellow precipitate).
(iii) Manganese dioxide and copper (II) oxide.
Ans: Heat each solid strongly with concentrated hydrochloric acid (conc. HCl) and note the gas evolved.
Manganese Dioxide (MnO₂): Will produce greenish-yellow chlorine gas (Cl₂), which has a bleaching effect and a pungent smell.
Copper (II) Oxide (CuO): Will produce no characteristic coloured gas; it will form a green-blue solution of copper(II) chloride.
(d) State your observation: A zinc granule is added to copper sulphate solution.
Ans: The shiny surface of the zinc granule becomes coated with a reddish-brown deposit of copper metal. Simultaneously, the characteristic blue colour of the copper sulphate solution slowly fades.
(e) Give a balanced equation for the reaction: Silver nitrate solution and sodium chloride solution.
Ans:
AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq)
2013
(a) Give a chemical test to distinguish between:
(i) Sodium chloride soln. and sodium nitrate soln.
(ii) Hydrogen chloride gas and hydrogen sulphide gas.
(iii) Calcium nitrate soln. and zinc nitrate soln.
(iv) Carbon dioxide gas and sulphur dioxide gas.
(b) Which one of the following will not produce an acid when made to react with water.
(i) Carbon monoxide
(ii) Carbon dioxide
(iii) Nitrogen dioxide
(iv) Sulphur trioxide
Ans: (a) Chemical tests to distinguish between the following pairs:
(i) Sodium chloride solution and sodium nitrate solution
Add a few drops of silver nitrate (AgNO₃) solution to each solution.The solution which forms a thick white precipitate is sodium chloride.The solution which shows no visible change or a slight curdy white precipitate (due to slight decomposition) is sodium nitrate.
(ii) Hydrogen chloride gas and hydrogen sulphide gas
Bring a rod dipped in ammonia solution near the mouth of each gas jar.The gas that produces dense white fumes is hydrogen chloride.The gas that has a distinct smell of rotten eggs and turns lead acetate paper silvery-black is hydrogen sulphide.
(iii) Calcium nitrate solution and zinc nitrate solution
Add ammonium hydroxide (NH₄OH) solution in excess to both solutions.
The solution that forms a white precipitate which does not dissolve in excess ammonium hydroxide is calcium nitrate.The solution that first forms a white precipitate, which then dissolves completely in excess ammonium hydroxide to form a clear, colourless solution, is zinc nitrate.
(iv) Carbon dioxide gas and sulphur dioxide gas
Bubble each gas through acidified potassium dichromate solution.The gas that changes the solution colour from orange to green is sulphur dioxide.The gas that has no effect on the orange colour is carbon dioxide.
(b) Which one of the following will not produce an acid when made to react with water?
(i) Carbon monoxide
Carbon monoxide (CO) is neutral and does not react with water to form an acid. The other gases (Carbon dioxide, Nitrogen dioxide, and Sulphur trioxide) all dissolve in water to form carbonic acid, nitric acid, and sulphuric acid, respectively.
2014
(a) Distinguish between: Sodium nitrate and sodium sulphite [using dilute sulphuric acid].
(b) State your observation: When moist starch iodide paper is introduced into chlorine gas.
(c) The flame test with a salt P gave a brick red flame. What is the cation in P?
(d) A gas Q turns moist lead acetate paper silvery black. Identify the gas Q.
(e) pH of liquid R is 10. What kind of substance is R?
Ans:
a) Distinguish between: Sodium nitrate and sodium sulphite [using dilute sulphuric acid].
When dilute sulphuric acid is added:
To Sodium Sulphite, it will react to produce sulphur dioxide gas (SO2 ). You can identify this gas by its sharp, choking smell (like burnt matches). This gas will also turn acidified potassium dichromate paper from orange to green.To Sodium Nitrate, there is no reaction with dilute sulphuric acid. No gas is evolved, and there is no smell.
(b) State your observation: When moist starch iodide paper is introduced into chlorine gas.
Answer: The moist starch iodide paper will turn a deep blue or blue-black colour.
(c) The flame test with a salt P gave a brick red flame. What is the cation in P?
Answer: The cation (positive ion) in salt P is Calcium (Ca2+ ).
(d) A gas Q turns moist lead acetate paper silvery black. Identify the gas Q.
Answer: The gas Q is Hydrogen Sulphide (H2S).
(e) pH of liquid R is 10. What kind of substance is R?
Answer:Since the pH is 10, which is greater than 7, the liquid R is a base or an alkaline solution.
