Chapter 16: Lab Safety and Practical Skills

Working in chemical laboratory • A chemistry laboratory is a chemist workshop. • It is a place where a student is trained to observe the physical and chemical characteristics of substances. • A student should get himself familiarized with the layout of the laboratory and various fittings provided on the laboratory table as well as the side shelves. General instructions to the students (i) Students are expected to conduct themselves in a responsible manner at all times in the lab. (ii) They are advised not to work alone in the lab: Experiments should be performed in the presence of lab instructor and other laboratory staff. Students should always wear lab coat and safety goggles while working in the (ill) lab. Girls must tie up their scarves and hair before start working in the lab. (iv) Determine the potential hazards related to any equipment or the experiment before starting any work. Appropriate safety precautions must be observed. (v) There must not be any crowding in the lab and students should stick to their work places at a safe distance from each other. (vi) Don't bring any food items in the lab. Never taste or smell any compound or a gas. (vii) Any accident or breakage of glassware must be reported to the incharge of the laboratory immediately t or an equipment properly then you must (vili) If you cannot handle an instr seek help from the instructor (1X) Do not pour chemicals down the drains and do not utilize the sewer for chemical waste disposal. (x) Follow the warning sign displayed in the lab.

While working in a laboratory, we may face various házards. These hazards are generally divided into three main categories: physical hazards, chemical hazards, and biological hazards. (i) Physical hazards Slips and falls • The most common physical hazards are slips and falls, especially on wet floors. • Workers should take precautions to prevent slipping, tripping, or falling. Handling broken glassware: • Cu2+-resistant gloves should be worn when handling broken glass to prevent cuts, abrasions, and skin injuries. • It is important to dispose of broken glassware in a designated container to avoid injury. (ii) Chemical hazards Safe use of chemicals Chemicals should always be used according to standard procedures. • Workers must be aware of each chemical's hazards and the necessary safety precautions to use them safely. Flammable Oxidizing Explosive Toxic Irritant Fig: Pictogram of chemical hazards (iii) Biological hazards Common biological hazards include allergens, infectious diseases from animals (zoonotic diseases), and viral infections. These are transferred from animals plants water and air to human. : Proper safety measures should be followed to prevent the spread of these diseases. ee 1 Corrosive Compressed gas Health hazard Environmental hazard

Waste disposal system for chemical Chemical waste cannot be disposed off in bins or sewer system. Most chemical wastes must be disposed off keeping in view the following rules and regulation of Environmental Protection Agency (EPA): (i) Store chemical wastes in proper containers. (ii) Label the chemical waste containers with the types of wastes, the date of waste and place of origin. These containers are then transferred to the allocated site where these are appropriately (i11) treated to dispose them off (iv) Chemical treatment of wastes involves neutralization, precipitation, ion exchange, oxidation or reduction. FIRST AID IN LABORATORY

First aid in laboratory Every laboratory must have a first aid box. Common accidents and their first aid treatments are given as: Table 16.1: Accidents and their first aid treatment First Aid Treatment Lype of Accident Cuts (i) Minor cuts (i) Remove the glass piece if any, apply a little methylated spirit or tincture iodine with a piece of cotton. Both act as disinfectant. (11) Serious cuts (ii) Apply pressure on the Cu2+ for about 10 minutes to stop bleeding. Consult a doctor. Eye Injuries (i) Acid in the eye (i) Wash thoroughly with water and then with 1% sodium bicarbonate solution. (ii). Alkali in the eye (ii) Wash with water followed by 1% boric acid solution. (iii)Do not rub the eyes. Remove the particle carefully with soft (iii)Foreign particle handkerchief then wash with water. in the eye (iv) Soreness in the (iv)Put a drop of olive oil in the-eyes and keep them closed form some time. eye Burns (i) Apply Burnol mustard oil (i) Burns with dry heat (flame, hot object (ii) Wash freely with ice cold water. Then wash with a saturated (ii) Acid burns solution of sodium bicarbonate and again with water (iii) Wash freely with water and then with 1% acetic acid solution (iii) Alkali burns and again with water, dry the skin and apply the Burnol. (iv) Wash fully with 2% ammonia solution and apply glycerine. (iv) Bromine burns Wipe off glycerine after sometime and apply Burnol. Poisons (i) Poisons (i) Spit immediately wash mouth with water repeatedly swallowed (ii) Drink a lot of water or lime water or milk of magnesia. (ii) Acid swallowed (iii) Caustic alkalies (iii)Drink a lot of water; drink a glass of lemon or orange juice. swallowed (iv) Take milk or white part of the egg. (iv) Salt of heavy metals swallowed Fire (i) Do not run. Wrap with blanket or with dry cotton cloth. Lie (i) Clothes catch fire down on the floor. (ii) Beaker (ii) Cover the beaker with a duster or damp cloth. This will Cu2+ off the supply of oxygen. containing inflammable liquid, catches fire. (iii) Throw a mixture of sand and sodium bicarbonate. Do not throw (iii)Spirit or oil al-water. It will simply spread the fire. catches fire. (iv) Switch off the electric supply immediately and throw sand. Do (iv) Electric parts not throw water in such cases to extinguish fire. catch fire. Quick Check 16.1 (a) Mention common types of hazard. Common types of hazards include: • Physical hazards (broken glass, fire) • Chemical hazards (toxic or corrosive chemicals) • Biological hazards (bacteria, viruses) • Electrical hazards (exposed wires) (b) How chemical waste is disposed off! Ans. Chemical waste cannot be disposed of in bins or sewer system. Most chemical wastes must be disposed of keeping in view the following rules and regulation of Environmental Protection Agency (EPA). (i) Store chemical wastes in proper containers (il) Label the chemical waste containers with the types of wastes, the date of waste and place of origin. (i11) These containers are then transferred to the allocated site where these are appropriately treated to dispose them off. (iv) Chemical treatment of wastes involves neutralization, precipitation, ion exchange, oxidation or reduction. (c) How H2SO4 burn is treated in the lab? Ans. If sulfuric acid (HzSO4) spills on skin: • Wash immediately with plenty of water for at least 15 minutes • Remove contaminated clothing • Seek medical help if irritation continues (d) What are different types of burns? Ans. Different types of burns include: • Thermal burns (caused by heat or fire) • Chemical burns (caused by acids or bases) • Electrical burns (caused by electric shock) ACID-BASE TITRATION

Acid-Baes titration Volumetric analysis is used to find the concentrations of solutions by means of a technique known as titration. In this technique a solution of unknown concentration is combined slowly and carefully with a known volume of a standard solution until a colour change shows the completion of the reaction. The substance which indicates the completion of reaction by the change in its colour is called an indicator. The moment at which the indicator changes colour is called the end point. Either acidic or basic solution can be taken in a burette with the other solution taken in a conical or a titration flask. Did you know? S.Q. How phenolphthalein as indicator works? Ans. Phenolphthalein solution is prepared by adding one gram of the indicator is 500cm of 50% ethanol. Use only one to two drops in 10cm of the solutions to be titrated. The color change is from pink to colorless as the pH decreases. The light pink color which marks the end point tends to fade gradually due to the interference of atmospheric carbon dioxide which slowly dissolves in the solution. Materials required Burette, pipette, funnel, conical flask, HCl solution, NaOH solution, phenolphthalein. Procedure of titration • Rinse the pipette with distilled water and NaOH solution. • Rinse the conical flask with distilled water. • Pipette 10cm' of NaOH into the conical flask and add 1-2 drops of phenolphthalein. The solution turns pink • Rinse the burette with distilled water and then Hcl solution. • Fill the burette with HCl using a funnel, then remove the funnel. • Release some acid to remove air bubbles and note the initial burette reading. • Place the conical flask on white paper under the burette and perform a rough titration by adding acid dropwise while swirling the flask. • When the pink color just disappears and the solution becomes colorless, note the final reading. • Repeat the titration to get accurate and concordant readings. Take at least three concordant readings which agree with one another within 0.1 cm? Initial reading Pipette Acid solution Dropper Indicator 2 Fig: Procedure of titration Observations Titration number Rough Reading Final reading Initial reading Volume of acid used (cm') (x-y) cm Volume of HCl solution used = The balanced chemical equation: NaOH (ag) + HC (aq) → NaClag) + H, 0(1) From the equation, ni = n2 = 1 Calculation Find out the molarity of NaOH solution by using the following molarity equation: MI= Molarity of acid solution VI=Volume of the acid used ni=No. of moles of the acid in the balanced chemical equation M2=Molarity of base solution V2= Volume of base solution used n2=No. of moles of the base in the balanced chemical equation _M. Molarity of the given base solution is Quick Check 16.2 (a) Define indicator and endpoint in a titration. Indicator An indicator is a chemical substance that changes color at a specific pH. It is used in titrations to show when the reaction is near completion. Burette Final reading . .. Hold Hold Release 5. 3. 3 Acid Base n, n2 Endpoint The endpoint is the stage in a titration when the indicator changes color, showing that the titration is complete and the acid has neutralized the base (or vice versa). (b) What is meant by concordant readings? Ans. Concordant readings are repeated titration results that agree with one another within a small margin, typically 0.1 cm (c) How the volume of the titrant used is calculated? Ans. The volume of titrant used in a titration is calculated by subtracting the initial volume of the titrant in the burette from the final reading after the reaction reaches the end point. TESTS FOR IDENTIFICATION OF ANIONS

(i) Identification of carbonate CO* radical Experiment Take about 2g of solid carbonate Effervescence sample in a clean test tube and during which a gas evolves then add about 5cm of dilute briskly, that turns lime water the gas Hcl solution. Pass turns milky. evolved in the above step through a solution of lime water treelm. Reactions involved in the above steps CO?- ( Identification of chloride (CI), bromide (Brand iodide (l') radicals. Experiment Take 2g of solid sample in a test tube A thick white precipitate 1s and 5cm of distilled water to make the aqueous solution. Add a few drops of • the dil. HNO solution to acidity solution of the salt, finally add about 5cm of aqueous Ag NO3 Reactions involved in the above tests Ag (ag) + Claq) white ppt → AgBr(s) Ag (ag) + Braq) cream yellow ppt A8 (ag) + (ay) → Ag (s) bright yellow ppt Observation Inference takes place are Carbonate CO?- indicated ions. Observation Inference are formed which dissolves in indicated ag. NH3 thick A Br ions are cream-yellow indicated precipitate is formed. ions are A bright yellow precipitate is formed indicated Did you know? S.Q. Why HNO is added in detection of halides? Ans. In the above tests for the detection of halide ions, dilute nitric acid is added to prevent the precipitation of carbonate ions along-with halide ions. Chloride (White) Bromide (Cream) Fig: Observation of reactions of halide ions with AgNO, (ill) Identification of Nitrate NO, radical Experiment Take 2g of solid sample in a A characteristic smell of clean test tube and dissolve it in NH3 gas is felt near the 5cm distilled water. Add to it mouth of test tube. This gas turns red litmus paper 5cm of sodium hydroxide solution. Finally add 3g blue. Ge! powdered aluminium metal. Aluminium metal reduces nitrate ions to ammonium ions which then react with aqueous NaOH to evolve ammonia gas. (iv) Identification of Sulphate SO* radical Experiment Take 3g of solid sample in a clean test A tube. Dissolve it in 5cm' of distilled water. Acidify the solution with a few drops of dil. HNO3 and then add 5cm barium nitrate solution. SO 3(ag) + Barat) → BaSO, (white ppt.) Did you know? S.Q. Why HNO added to carbonate solution? Ans. Dilute nitric acid is added to destroy any carbonate ions present in the solution as an impurity. iodide (Yellow) Observation Inference NO, indicated. Inference Observation heavy white SO, ions are indicated precipitate of BaSO is formed. (s) Quick Check 16.3 (a) Distinguish between carbonate (CO;) and bicarbonate (HCO3 ) radicals. Ans. • Carbonate (CO3 ): Reacts with dilute acid to produce carbon dioxide gas rapidly with effervescence. Test: CO3 + 2HCI → CO2 + H20 + 2Cl- • Bicarbonate (HCO3 ): Also reacts with dilute acid, but the reaction is slower and less vigorous. Test: HCO5 + Hcl → CO2 + H20 + CH • Difference: Carbonate gives brisk effervescence. (b) What is ring test? Give equation for this test. Ans. Ring Test It is a confirmatory test for nitrate (NOs) ions. When freshly prepared FeSO4 solution is added to a nitrate solution, and concentrated H2SOa is added along the sides of the test tube, a brown ring appears at the junction. Reaction → FeSO,. NO FeSO, + NO- Brown Ring Nitric oxide (NO) reacts with Fet to form a brown ring of [Fe(H2O)s(NO)|*+. (c) Give names and formulas of some water-insoluble sulphates. Ans. Some water-insoluble sulphates are: • Barium sulphate - BaSO4 • Lead(II) sulphate - PbSO4 • Calcium sulphate (sparingly soluble) - CaSO4 • Strontium sulphate - SrSO4 TESTS FOR IDENTIFICATION OF BASIC RADICALS

(i) Al* (i) NH; (iii) Ca?+ (iv) Cr3+ (V) Cu2+ (vi) Fe2+ (vii) Fe3+ (vili) Zn2+ (i) Identification of Aluminium (Al3+) radical Take 4g of solid sample in a clean test tube. Dissolve it in about 10cm distilled water Divide this solution into two parts for further tests. Experiment To one part, add about 5 cm NaOH solution To the second part of the above solution, add a few drops of aqueous ammonia. Al3+ mild effervescence; bicarbonate gives Observation Inference white Al+ ions gelatinous are indicated precipitate is formed Al'+ A white precipitate is ions are formed indicated white ppt. (* Identification of Ammonium (NH*) radical Experiment Take 4g of sample in a clean test tube. Dissolve it in 10 cm distilled water cma distilled water: Amma dials, Add NaOH solution and gently heat it. NH 4(ag) + OH ac (i) Identification of Calcium (Cat) radical Take 4 g solid sample in a clean test tube. Dissolve it in 10 cm distilled water Make two parts of this solution for further tests. Experiment To one part, add NaOH solution. To the second part of the above solution, add aqueous ammonia. (aq) Ca (a) + 20H (iv) Identification of Chromium radial (Crt) Add 4 g sample in a clean test tube. Dissolve it in 10 cm distilled water. Make two parts of the above solution for further tests. Experiment To one part, add NaOH solution. To the second part of the above solution, add aqueous ammonia. (rat) + 30H (ag) (V) Identification of copper radical (Cu2+) Add: 4g solid sample in a clean test tube. Dissolve it in 10cm' of distilled water. Make two parts of the above solution for further tests. Observation Experiment add NaOH To first part, Light-blue formed solution. Deep blue solution is formed. To the second part of the above solution, add aqueous ammonia. (u ay) + 20H (aq) Inference Observation Ammonia gas is evolved NH, indicated with a distinct smell turns Ammonia gas moist red litmus blue. → NH 3(8) + H, 0(e) Observation Inference is Cal indicated White precipitate dissolve in excess dissolve which does not NaOH solution. Cal indicated Only a slight turbidity Or No appears precipitate is formed white ppt. Inference Observation Crt indicated a green precipitate appears which turns into when green solution excess of NaOH is added. Crt indicated Green precipitate is which appears insoluble in excess of aqueous ammonia. Green ppt. Inference Cu2+ indicated precipitate Cu2+ indicated Blue ppt. (vi) Identification of ferrous radical (Fet) Add 4g solid sample in a clean test tube. Dissolve it in 10cm' of distilled water. Make two parts of the above solution for further tests. Observation Experiment Green precipitate is formed Fet indicated To one portion, add NaOH solution. which is turned into orange brown precipitate after some time. White gelatinous precipitate To the second potion of the of Fe(OH)2 is formed which above solution, add aqueous ammonia. quickly oxidizes to form red brown precipitate of Fe(OH)3. Felay) + 20H (aa) - (vii) Identification of Fe(TIl) radical (Fe*) Take 2g FeCl in a clean test tube. Dissolve it in. 10cm' of distilled water. Make two portions of the solutions for further tests. • Observation Inference Experiment-= 6J6 add NaOH Orange brown precipitate To one portion, is formed. solution. To the second portion of the Orange brown precipitate is formed. above solution, add aqueous ammonia. Fe(a4) + 30Н (a) → Fe(OH) 3(0) (vili) Identification of Zine radical (Zn2+) Take 4g solid sample in a clean test tube. Dissolve it in 10cm? of distilled water. Make two portions of the above solution for further tests. Observation Experiment White precipitate is formed To one portion, add NaOH which is soluble in excess of solution. NaOH solution. White precipitate is formed To the second portion of which dissolves the above solution, add ammonia. aqueous ammonia. Z (ag) + 2OH (ag) = Inference Fet indicated → Fe(OH)2 Green ppt. Fe3+ ions are indicated Fe3+ ions are indicated. Orange brown ppt. Inference •Zn2+ ions are indicated. Zn2+ ions are indicated. in excess of → Zn(OH)2(5) White ppt. Quick Check 16.4 (a) What is lake test? Give equation. Ans. Lake Test: It is a confirmatory test for aluminium ions (Al3+). When Al3+ reacts with NH OH, a white gelatinous precipitate of Al(OH) forms. In the presence of dye (like alizarin), a red lake (colored complex) is formed. Equation Al** + 3NH_OH → AI (OH), 4 + 3NH; (b) How is ammonium ion (NH+*) indicated? Ans. Ammonium ion is indicated by: • Warming with NaOH: It releases ammonia gas (NH3), which has a pungent smell. • The gas turns red litmus blue, confirming basic nature. Test NH; + OH → NH, T +H2O (c) How will you distinguish between ferrous and ferric radicals? The identification of Fet (ferrous ion) and Fe3+ (ferric ion) can be distinguished using chemical tests based on their different colors and reactions with reagents. (d) What happens when aqueous NH is added to Cu2+ solution in limited and excess quantities? • Limited amount: Forms a precipitate of metal hydroxide (e.g., Cu(OH) for copper). • Excess amount: The precipitate dissolves, forming a soluble complex (e.g:, deep, blue [Cu(NH3)4] + for copper). Example Cu2+ + 2NH3 + 2H2O → Cu(OH)21 + 2NH* Cu(OH)2 + 4NH3 → [Cu(NH3)4]12+ + 20H