General Chemistry Practical Safety Rules 2024-2025
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Questions and Answers

What color did the solution plus FeCl3 produce initially?

  • Crimson red
  • Dark violet (correct)
  • Pale green
  • Bright yellow

What change occurred to the dark violet color over time?

  • It decolorized (correct)
  • It turned bright orange
  • It became dark blue
  • It remained unchanged

Which substance is identified as A.R in the given content?

  • Hydrochloric acid
  • Potassium permanganate
  • Sodium chloride
  • Thiosulphate (correct)

What could be inferred about the interaction of thiosulphate with the solution?

<p>It contributes to the decolorization (A)</p> Signup and view all the answers

What chemical change does the presence of FeCl3 indicate?

<p>Oxidation of thiosulphate (A)</p> Signup and view all the answers

What happens when a substance is reacted with HCl?

<p>It forms white fumes. (A)</p> Signup and view all the answers

What is the effect of a certain substance on litmus paper?

<p>It turns red litmus paper blue. (B)</p> Signup and view all the answers

What precipitate is formed when a solution is treated with Nessler's reagent?

<p>Brown precipitate. (B)</p> Signup and view all the answers

Which ion is indicated by the formation of a white precipitate when combined with Na3PO4?

<p>Mg2+ (D)</p> Signup and view all the answers

What does the reaction of a solution containing Mg2+ and NH4Cl yield?

<p>A white precipitate (C)</p> Signup and view all the answers

Which statement is true regarding the use of Nessler's reagent?

<p>It is used to confirm the presence of certain substances. (A)</p> Signup and view all the answers

Which of the following is a characteristic odor related to some chemical reactions?

<p>Pungent and sharp. (D)</p> Signup and view all the answers

Which ion is typically tested with Na2CO3 to produce a white precipitate?

<p>Mg2+ (D)</p> Signup and view all the answers

Which combination of reagents leads to the precipitation of Sr2+ ions?

<p>NH4Cl and Na2CO3 (A)</p> Signup and view all the answers

After boiling or scratching, which ion is reduced negatively indicated by the reaction sequence provided?

<p>Sr2+ (B)</p> Signup and view all the answers

What should be done with a heated object before placing it on the balance?

<p>Cool it first. (A)</p> Signup and view all the answers

When diluting acid, which method is considered correct?

<p>Always pour acid into water. (A)</p> Signup and view all the answers

Why is it important never to pour water into acid during dilution?

<p>It can cause an exothermic reaction. (C)</p> Signup and view all the answers

Which of the following statements is true regarding handling heated objects?

<p>They should be cooled before weighing to prevent balance damage. (C)</p> Signup and view all the answers

What is the primary reason for adding acid to water rather than the other way around?

<p>To minimize the risk of splattering. (A)</p> Signup and view all the answers

What effect does the addition of NH4Cl have on the concentration of hydroxide ions, [OH-]?

<p>It decreases [OH-] (B)</p> Signup and view all the answers

Which of the following statements best explains the common ion effect in the context given?

<p>The presence of NH4+ reduces the solubility of the compound. (C)</p> Signup and view all the answers

Which of these reactions shifts to the left upon the addition of NH4Cl?

<p>NH4OH ⇌ NH4+ + OH- (D)</p> Signup and view all the answers

When NH4OH is added, what effect is observed on the concentration of S2-?

<p>The concentration of S2- increases. (A)</p> Signup and view all the answers

What precipitate forms in the presence of NH4Cl and decreased [OH-]?

<p>Group II precipitate (D)</p> Signup and view all the answers

Which statement accurately describes the solubility of the precipitate formed with nitric acid?

<p>The precipitate is insoluble when the anion is a sulphate. (B), The precipitate formed is soluble if the anion is a phosphate or borate. (D)</p> Signup and view all the answers

What type of precipitate is formed when testing for sulphate with nitric acid?

<p>White precipitate (B)</p> Signup and view all the answers

Which anions are suggested to result in a soluble precipitate when reacted with nitric acid?

<p>Phosphate and borate (D)</p> Signup and view all the answers

When testing for the presence of sulphate using nitric acid, what could be the result of the test?

<p>It may yield an insoluble precipitate. (A)</p> Signup and view all the answers

Which of the following is a likely result for an acid reaction involving a sulphate ion?

<p>Formation of a white precipitate. (C)</p> Signup and view all the answers

Flashcards

Safety Rule: Heated Objects on Balance

Never place a heated object directly on the balance. Allow it to cool down first.

Diluting Acid

Always add acid to water, never the other way around.

Why Diluting Acid is Dangerous

Adding water to acid can create a violent exothermic reaction, potentially causing splashes and burns.

Exothermic Reaction

A chemical reaction that releases heat into the surroundings.

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Acid Dilution Safety

The process of diluting acid requires careful addition of acid to water, with constant stirring, to control the heat released.

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FeCl3

Iron (III) chloride is a chemical compound, used in a variety of applications including water treatment, etching, and manufacturing.

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Dark violet color

The solution with FeCl3 exhibits a distinctive dark violet color.

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Decolorized with time

The dark violet color of the solution fades or disappears over time.

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Thiosulphate

Thiosulphate is a chemical compound (like a salt) that can react with FeCl3 to decolorize the solution.

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A.R

A.R. stands for Analytical Reagent, indicating a high purity and quality of the chemical compound.

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Ammoniacal Odor

The characteristic smell of ammonia, often described as pungent or sharp.

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White Fumes with HCl

When ammonia gas reacts with hydrochloric acid (HCl), it produces dense white fumes of ammonium chloride (NH4Cl).

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Turns Red Litmus Paper Blue

Ammonia is basic, meaning it increases the hydroxide ion concentration (OH-) in solution. Litmus paper turns blue in the presence of a base.

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Nessler's Reagent Test

Nessler's reagent (K2[HgI4]) is used to detect the presence of ammonia. A brown precipitate indicates a positive test.

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Confirmatory Test for Ammonia

A confirmatory test confirms the presence of a substance by providing additional evidence. Nessler's reagent is a confirmatory test for ammonia.

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Sr2+ Detection

Strontium ions (Sr2+) can be detected by heating a sample in a Bunsen burner flame. If the flame turns a crimson red color, it indicates the presence of strontium ions.

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Ca2+ Detection

Calcium ions (Ca2+) can be detected by adding sodium carbonate (Na2CO3) to a solution. If a white precipitate forms, it indicates the presence of calcium ions.

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Mg2+ Detection (1)

Magnesium ions (Mg2+) can be detected by adding ammonium chloride (NH4Cl), ammonium hydroxide (NH4OH), and sodium phosphate (Na3PO4) to a solution. If a white precipitate forms, it indicates the presence of magnesium ions.

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Mg2+ Detection (2)

Magnesium ions (Mg2+) can also be detected by adding sodium carbonate (Na2CO3) to a solution. If a white precipitate forms, it indicates the presence of magnesium ions.

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Nitric Acid Test (Nitrate)

This test helps identify if a substance contains nitrate ions. It involves adding nitric acid to the solution. If a precipitate forms, it indicates the presence of a specific anion, and if it doesn't, it suggests another possible anion.

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Insoluble Precipitate with Nitric Acid

A precipitate that does not dissolve in nitric acid is usually a sign that the substance contains sulfate ions. The presence of an insoluble precipitate indicates the absence of phosphate or borate.

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Soluble Precipitate with Nitric Acid

If the precipitate dissolves in nitric acid, it suggests the presence of phosphate or borate ions. This is because their precipitates tend to dissolve in nitric acid.

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Confirmatory Test for Sulfate

This test provides additional confirmation for the presence of sulfate ions. It is performed by adding a specific reagent (usually barium chloride) to the solution. A white precipitate indicates the presence of sulfate.

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Confirmatory Test with Barium Chloride

This test uses barium chloride to identify the presence of sulfate. When barium chloride is added to a solution containing sulfate ions, a white precipitate is formed. This is a definitive sign of sulfate ions in the solution.

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Group III Precipitation with NH4Cl

Group III cations precipitate as hydroxides in the presence of NH4Cl. The addition of NH4Cl decreases the hydroxide ion concentration ([OH-]), preventing the precipitation of Group II cations.

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Common Ion Effect in Group III Precipitation

The presence of NH4Cl introduces a common ion (NH4+) to the equilibrium of NH4OH dissociation, shifting the equilibrium to the left, decreasing the concentration of OH- ions.

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Effect of NH4Cl on Ksp of Group III

Decreasing the [OH-] by adding NH4Cl reduces the Ksp value for Group III hydroxides, making them less soluble and promoting precipitation.

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Solubility of Group II vs. Group III

Group II cations are more soluble than Group III cations. Adding NH4Cl helps to selectively precipitate Group III cations, leaving Group II cations in solution.

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Selective Precipitation with NH4Cl

NH4Cl is used to selectively precipitate Group III cations by decreasing the [OH-] and making the precipitation of Group III hydroxides more favorable, while leaving Group II cations in solution.

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Study Notes

General Chemistry Practical

  • Intended for first-year students in 2024-2025
  • Taught by Dr. A.E.

Safety Rules

  • Wear protective clothing (lab coat, safety glasses, closed shoes/gloves)
  • Never work in the lab without an instructor
  • Avoid unauthorized experiments
  • Do not remove reagents from designated areas
  • Do not taste chemicals or use pipettes to taste chemicals
  • Do not return unused chemicals to the original containers
  • Do not point, look at or smell reagent test tubes directly
  • Do not use droppers, pipettes or spatulas inside reagent bottles
  • No food, drink, contact lenses, or gum in the lab
  • Clean and dry all equipment and benches before starting

Heating Chemicals

  • Point the test tube away from yourself and others during heating
  • Use a test tube holder to hold it at an angle over the flame
  • Continuously move the test tube during heating
  • Never heat flammable liquids directly over an open flame
  • Cool heated objects before placing them on a balance

Diluting Acids

  • Always add acid to water, never water to acid

Waste Disposal

  • Dispose of liquids and water-soluble chemicals in the sink
  • Dispose of hazardous organic liquids in special containers in the fume hood
  • Dispose of insoluble solids and broken glassware in the waste basket

Leaving the Lab

  • Return all equipment and chemicals to their proper places
  • Thoroughly clean all equipment 15 minutes before the end of the lab

Material Safety Data Sheets (MSDS)

  • MSDS documents contain information about the hazards of a chemical material
  • Includes information about potential hazards

Hazards

  • Chemical hazards (toxic, corrosive, irritant, explosive)
  • Biological hazards (pathogenic microbes)
  • Physical hazards (noise, radiation)
  • Mechanical or electrical hazards (high voltage)
  • Psychological hazards

Hazard Rating Systems

  • NFPA uses a color-coded system to indicate the level of hazard for different materials (red for flammability, yellow for reactivity)

Hazards Exposure Limits

  • Lethal Concentration 50 (LC50): Concentration of a chemical that causes death in 50% of test animals exposed by inhalation
  • Lethal Concentration Low (LCLo): Lowest concentration of a chemical that causes death in one human or animal exposed by inhalation
  • Lethal Dose 50 (LD50): Dose of a chemical causing death in 50% of test animals when exposed through routes other than inhalation
  • Lethal Dose Low (LDLo): Minimum amount of a chemical that causes death in one human or animal when exposed through routes other than inhalation

Laboratory Equipment and Glassware

  • Test tubes
  • Beakers
  • Watch glasses
  • Droppers
  • Test tube racks
  • Test tube brushes
  • Test tube holders
  • Reagent bottles

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General Chemistry Practical 2024-2025 PDF

Description

This quiz covers the essential safety rules and procedures for conducting experiments in the General Chemistry laboratory. Designed for first-year students, it emphasizes the importance of safety precautions to ensure a secure laboratory environment. Master these guidelines to prepare effectively for your chemistry practicals.

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