Selina Concise Solutions for ICSE Class 10 Chemistry Chapter 13 Practical Work

Exercise 1

Solution 1.
(a) (i) Chemical test for ammonia:
If a rod dipped in concentrated hydrochloric acid is brought near ammonia gas, dense white fumes of ammonium chloride (\( \text{NH}_4\text{Cl} \)) are formed.
(ii) Chemical test for Sulphur dioxide:
It decolorizes pink coloured potassium permanganate solution.
(iii) Chemical test for HCl:
When HCl gas is passed through \( \text{AgNO}_3 \) solution, white precipitates of AgCl are formed which gets dissolved in excess of \( \text{NH}_4\text{OH} \).
(iv) Chemical test for Chlorine:
It turns moist starch iodide paper (KI + starch solution) blue black.
(v) Chemical test for Carbon dioxide:
When this gas is passed through lime water, it turns milky due to the formation of white precipitates of \( \text{CaCO}_3 \) and on passing excess of carbon dioxide gas, this milkiness disappears.
(vi) Chemical test for oxygen:
This gas is absorbed in colourless alkaline solution of pyrogallol and turns it dark brown.
(vii) Chemical test for hydrogen:
It burns with a pop sound when a burning taper is brought near it.
(b) Ammonia is a basic gas and its basic nature is suspected through litmus paper test because it changes the colour of red litmus paper to blue.
(c) Chlorine, carbon dioxide, hydrogen chloride, hydrogen sulphide and sulphur dioxide are acidic gases since they convert blue litmus to red.
(d) A is chlorine and B is Sulphur dioxide.
(e) Water vapour.
Answer: Chemical tests help identify gases based on their unique reactions with specific reagents. Each gas produces characteristic color changes, precipitates, or other observable changes that allow us to confirm its identity.

📝 Teacher's Note: Demonstrate these tests with actual gases in a well-ventilated lab. Students often confuse the color changes, so create a comparison chart showing before and after results for each test.

🎯 Exam Tip: Remember the key phrases: "dense white fumes" for ammonia test, "milky then clear" for CO₂, and "pop sound" for hydrogen. These exact descriptions earn full marks.

Solution 2.
(a) \( \text{O}_2 \)
(b) \( \text{NH}_3 \)
(c) Water vapour
(d) \( \text{SO}_2 \)
Answer: The answers identify specific gases based on their properties and behavior in different tests.

📝 Teacher's Note: Connect each answer to the chemical tests from Solution 1. Ask students to explain why each gas was chosen for each part.

🎯 Exam Tip: Write chemical formulas correctly with proper subscripts and superscripts to avoid losing marks for notation errors.

Solution 3.
(a) \( \text{Na}_2\text{CO}_3 \) and \( \text{K}_2\text{CO}_3 \)
(b) \( \text{SO}_2 \)
(c) \( \text{CO}_2 \)
(d) \( \text{Cl}_2 \)
(e) \( \text{H}_2\text{S} \)
Answer: These are specific chemical compounds and gases that can be identified through various chemical tests and their distinctive properties.

📝 Teacher's Note: Help students understand the difference between compounds (like carbonates) and elements (like gases). Use molecular models if available.

🎯 Exam Tip: Double-check chemical formulas for correct capitalization and subscripts - \( \text{CO}_2 \) not Co2 or co2.

Solution 4.
Silver nitrate and ammonium nitrate.
Answer: These are the two nitrate compounds that can be distinguished using specific chemical tests based on their different cations (silver vs ammonium).

📝 Teacher's Note: Demonstrate how the silver ion and ammonium ion react differently with the same reagents, making identification possible.

🎯 Exam Tip: When naming compounds, always include both the cation and anion names completely for full marks.

Solution 5.
(a) \( \text{Cl}^- \)
(b) \( \text{SO}_4^{2-} \)
(c) \( \text{CO}_3^{2-} \)
(d) \( \text{SO}_3^{2-} \)
Answer: These are anions (negatively charged ions) that can be identified through specific precipitation tests and color reactions.

📝 Teacher's Note: Emphasize the importance of writing correct charges on ions. Practice drawing the electron configurations to show why these charges occur.

🎯 Exam Tip: Always include the correct charge notation (superscript) when writing ions - examiners deduct marks for missing charges.

Solution 6.
(a) Since the salt solution turned blue litmus red hence the salt may be an acid.
(b) Since addition of barium chloride into the solution of salt gave white precipitate so the salt may contain \( \text{SO}_4^{2-} \), \( \text{SO}_3^{2-} \), \( \text{CO}_3^{2-} \) anion.
(c) The flame test of the salt gives persistent golden yellow colourisation which suggests presence of \( \text{Na}^+ \) ion.
Answer: These are analytical observations that help identify the components of an unknown salt through litmus test, precipitation test, and flame test respectively.

📝 Teacher's Note: Conduct actual flame tests to show students the distinctive colors. Sodium's golden yellow is very characteristic and easy to remember.

🎯 Exam Tip: Link each observation to a specific test - "litmus test shows acidity," "barium chloride test shows sulfate/carbonate," "flame test shows sodium."

Solution 7.
(a) \( \text{Ca}^{2+} \)
(b) \( \text{Cu}^+ \)
(c) The three ways are:
1. Ammonia gas turns moist red litmus blue.
2. If a rod dipped in concentrated HCl is brought near the gas, dense white fumes of \( \text{NH}_4\text{Cl} \) are formed.
3. The gas turns colourless Nessler's reagent i.e. \( \text{K}_2\text{HgI}_4 \) brown.
Answer: Part (a) and (b) identify specific metal cations, while part (c) describes three different methods to confirm the presence of ammonia gas.

📝 Teacher's Note: Show students that having multiple tests for the same substance increases confidence in identification. Nessler's reagent is very sensitive to ammonia.

🎯 Exam Tip: For "three ways" questions, number your answers clearly (1, 2, 3) and ensure each method is distinctly different.

Solution 8.

Answer: This comparative table shows how different gases react with litmus indicators and burning splints, helping distinguish between acidic, basic, and neutral gases.

📝 Teacher's Note: Use this table as a reference chart in the lab. Students should understand that only ammonia is basic (turns red litmus blue) while the others are acidic.

🎯 Exam Tip: When drawing tables in exams, keep them neat and ensure all cells are filled. Missing entries lose marks even if other parts are correct.

Solution 9.
(P) Ammonium chloride
(Q) Calcium
(R) Calcium hydroxide
(S) Lead (II) Nitrate
(T) Calcium Oxide
(U) Lead (II) Oxide
(V) Chlorine
(W) Hydrogen chloride
Answer: These are chemical compounds and elements identified by their letters, likely from a previous question or diagram showing their chemical properties and reactions.

📝 Teacher's Note: Ensure students understand the naming conventions for compounds, especially the use of Roman numerals for metals with multiple oxidation states like Lead (II).

🎯 Exam Tip: When writing compound names, always include oxidation states in Roman numerals where applicable - "Lead (II)" not just "Lead".

Solution 10.

Answer: This table shows the characteristic colors produced when different metal carbonates are heated and then cooled, which helps in identifying the metal present.

📝 Teacher's Note: Demonstrate the heating of these carbonates safely. The color change on cooling is due to the formation of metal oxides with different colors.

🎯 Exam Tip: Remember the color pattern: white for zinc, yellow for lead, black for copper. These are standard results that appear frequently in exams.

Solution 11.
(i) Sodium carbonate and sodium sulphite can be distinguished by using acidified \( \text{K}_2\text{Cr}_2\text{O}_7 \):
Take a small quantity of salt in a test tube; add dil. \( \text{H}_2\text{SO}_4 \) and warm if necessary. Now if on bringing a filter paper moistened with acidified \( \text{K}_2\text{Cr}_2\text{O}_7 \) near the gas evolved, the orange colour of the paper turns green then it is sodium sulphite.
(ii) Sodium thiosulphate and sodium sulphite:
The salts can be distinguished by using silver acetate. To the salt silver acetate and dil. \( \text{HNO}_3 \) are added. If there is formation of a white precipitate which slowly turns black then it is thiosulphate anion since silver acetate forms \( \text{Ag}_2\text{S}_2\text{O}_3 \) which being unstable in acid solution gets converted to black \( \text{Ag}_2\text{S} \).
(iii) Sodium hydroxide solution and ammonium hydroxide solution:
These salts can be distinguished by using a metal cation like calcium. When we add calcium salt to sodium hydroxide and ammonium hydroxide, then a white curdy ppt. is formed only in case of sodium hydroxide.
(iv) Ammonium sulphate and sodium sulphate:
These salts can be distinguished by using KOH. When KOH is added to ammonium sulphate, ammonia gas is evolved. Whereas there is no evolution of ammonia gas in case of sodium sulphate.
(v) Add barium chloride solution to sulphuric acid, nitric acid and hydrochloric acid. A white precipitate is formed in dilute sulphuric acid, and no such precipitate is formed in nitric acid and hydrochloric acid.
\( \text{BaCl}_2(\text{aq}) + \text{H}_2\text{SO}_4(\text{aq}) \rightarrow \text{BaSO}_4(\text{s}) + 2\text{HCl}(\text{aq}) \)
Answer: These are systematic methods to distinguish between similar chemical compounds using specific reagents that produce different reactions with each compound.

📝 Teacher's Note: These are classic analytical chemistry techniques. Emphasize the importance of observing color changes, gas evolution, and precipitate formation carefully.

🎯 Exam Tip: For distinction questions, always state the reagent used, the observation for each compound, and the conclusion clearly in separate lines.

Solution 12.
(a) Lead chloride as precipitate and sodium nitrite are formed.
(b)

(c) Dilute sulphuric acid liberates carbon dioxide from metallic carbonates and bicarbonates. Carbon dioxide when bubbled into a test tube containing calcium hydroxide solution turns it milky.
Answer: Part (a) describes a precipitation reaction, part (b) shows how to distinguish zinc salts using different reagents, and part (c) explains the test for carbonates using acid and lime water.

📝 Teacher's Note: Connect the white precipitate in part (b) to the formation of barium sulfate, which is insoluble. This is a classic test for sulfate ions.

🎯 Exam Tip: For tables showing reactions, clearly state "No reaction" rather than leaving cells blank to show you considered each possibility.

Solution 1 (2004).

Answer: This table shows the characteristic colors and solubility behavior when sodium hydroxide is added to different metal salt solutions, which helps identify the metal cations present.

📝 Teacher's Note: Emphasize the difference between "white gelatinous" (zinc) and "white chalky" (lead) - the texture is important for proper identification.

🎯 Exam Tip: Learn the specific descriptive words: "gelatinous" for zinc, "chalky" for lead, "curdy" for calcium, and "reddish brown" for iron (III).

Solution 1 (2005).
(I) Iron (II) Sulphate and Magnesium sulphate
(II) Iron (III) chloride and Zinc Chloride
(III) Lead nitrate
(IV) Copper nitrate.
(V) Lead nitrate.
Answer: These are chemical compounds that can be distinguished through various analytical tests based on their metal cations and anions.

📝 Teacher's Note: Help students understand the difference between Iron (II) and Iron (III) compounds and how they give different colored precipitates with reagents.

🎯 Exam Tip: Always specify the oxidation state of metals like iron - write "Iron (II)" or "Iron (III)" clearly to avoid confusion.

Solution 1 (2006).
(a) When alkaline phenolphthalein solution is added to acids then the colourless solution remains colourless.
(b) Orange colour of methyl orange indicator turns pink when the indicator is added to acids.
(c) Neutral litmus solution turns red on addition to acids.
Answer: These describe how different acid-base indicators behave when added to acidic solutions, showing characteristic color changes that help identify acids.

📝 Teacher's Note: Demonstrate with actual indicators to show these color changes. Students often confuse which indicator changes to which color in acids vs bases.

🎯 Exam Tip: Remember: phenolphthalein stays colorless in acid, methyl orange turns pink in acid, and litmus turns red in acid. Don't mix up these patterns.

Solution 1 (2007).

Answer: This matching table shows different salts (A through E) and their corresponding anions, identified through various analytical tests.

📝 Teacher's Note: Use this as a practice exercise for students to explain which tests would be used to identify each anion in the table.

🎯 Exam Tip: When writing ion formulas, ensure charges are correctly placed as superscripts and are mathematically balanced in the complete compound formula.

Solution 1 (2008).
(a) Iron (II) sulphate
(b) (I) Ammonia (\( \text{NH}_3 \))
(II) Dilute nitric acid (\( \text{HNO}_3 \))
(III) \( \text{H}_2\text{S} \)
(IV) Chlorine (\( \text{Cl}_2 \))
(V) Ethanol
Answer: Part (a) identifies a specific iron compound, while part (b) lists various chemical substances including gases, acids, and organic compounds that can be identified through characteristic tests.

📝 Teacher's Note: Point out that ethanol is an organic compound while the others are inorganic, requiring different types of tests for identification.

🎯 Exam Tip: Include chemical formulas in parentheses when naming compounds to demonstrate complete understanding and earn maximum marks.