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Acid-Base Titration
Q.1
For which type of titration methyl orange used as an indicator?
Correct Verbatim Answer
Methyl orange is used for strong acid-weak base titrations because it changes color in the acidic pH range (around pH 3.1- 4.4), making it suitable for detecting the acidic end point.
Q.2
Explain why phenolphthalein is a suitable indicator for the titration of a weak acid with a strong base but not for the titration of a strong acid with a weak base.
Correct Verbatim Answer
In a weak acid-strong base titration, the equivalence point lies in the basic pH range where phenolphthalein changes color (pH 8.3-10). However, in a strong acid- weak base titration, the equivalence point is would remain acidic, so phenolphthalein colorless and is unsuitable.
Q.3
Explain why different indicators change color over different pH ranges.
Correct Verbatim Answer
Each indicator is a weak acid or base and has a unique pKa value. The color change occurs over a specific pH range where the ratio of the protonated and deprotonated. forms changes, leading to visible color changes.
Q.3
Describe common types of the Chemistry lab hazards with two examples in each case.
Correct Verbatim Answer
See Q.2 from theory. What are common accidents in the
Q.4
Why is it always advisable to use dilute solutions while performing experiments in volumetric analysis?
Correct Verbatim Answer
Dilute solutions help to avoid sudden or violent reactions, ensure more accurate titration results, and make color changes easier to detect near the end point.
Lab Safety Rules
Q.4
Chemistry lab? How they are managed in first aid treatment.
Correct Verbatim Answer
See Q.4 from theory. Inference Crt ions are indicated. Crt ions are indicated. Green ppt Inference NHt ions are indicated Inference .Cations are indicated. Cations are indicated. white ppt
Basic Radicals
Q.5
White precipitates are formed when Ca2+, Al3+ and Zn2+ all react separately with NaOH solution. How will you detect which basic radical is present?
Correct Verbatim Answer
•Cat: Precipitate of Ca(OH)2 is insoluble in excess NaOH. • Al3+: Precipitate of AI(OH)з dissolves in excess NaOH forming a colorless solution. • Zn?+: Zn(OH)2 also dissolves in excess NaOH but can be confirmed with HaS, forming a white precipitate of ZnS.
Q.5
How the following acid radicals are indicated and confirmed in salt analysis: (i) CO, (ii) Cl (ili) NO; (iv) SO%
Correct Verbatim Answer
See Q.6 from theory
Q.6
How can Fet be distinguished from Fe3+ chemically?
Correct Verbatim Answer
•Add potassium ferricyanide: Fet gives a blue precipitate (Turnbull's blue). • Add potassium thiocyanate: Fe3+ gives a deep red solution due to the formation of Fe(SCN)3.
Q.6
How the following basic radicals are indicated and confirmed in salt analysis: (i) Cu?+ (i) ARt (iii) Fe3+ (iv) Zn?+
Correct Verbatim Answer
See Q.7 from theory.
Q.7
Why does Cat not give a precipitate with aqueous ammonia?
Correct Verbatim Answer
Aqueous ammonia does not produce a sufficiently high OH concentration to precipitate Ca(OH)2 due to its low solubility product (Ksp); hence, no visible precipitate forms.
Q.8
How wilt you find out the concentration of acetic acid in vinegar solution?
Correct Verbatim Answer
By performing an acid-base titration using NaOH of known concentration as the titrant and phenolphthalein as the indicator. The volume of NaOH used to reach the end point is used in the molarity equation to calculate the acetic acid concentration. precautions must
Q.9
What you observe while diluting a concentrated acid?
Correct Verbatim Answer
Always add acid to water slowly, never the reverse, while stirring violent continuously. This prevents splashing due to the exothermic nature of the dilution.
Q.10
Why does an aqueous solution of NazCO: behave like a base? ion (CO3=) carbonate
Correct Verbatim Answer
The hydrolyzes in water to form OH ions, making the solution basic. SLO BASED SHORT ANSWER QUESTIONS
Acid-Base Titration
Q.11
If an aqueous solution of NaOH is kept in an open container, what changes do you expect to take place over time?
Correct Verbatim Answer
NaOH absorbs carbon dioxide (CO2) from air, forming sodium carbonate (Na2CO3), thus reducing the concentration of hydroxide ions in the solution over time.
Q.12
What is titration?
Correct Verbatim Answer
Titration is a volumetric analysis the technique used to determine concentration of a solution by reacting it with a standard solution of known concentration until the reaction reaches completion.
Q.13
What is the role of an indicator in titration?
Correct Verbatim Answer
An indicator is a substance that shows the completion of a reaction by changing its color.
Q.14
Name the indicator used in the acid-base titration.
Correct Verbatim Answer
Phenolphthalein.
Q.15
Why is the funnel removed after filling the burette?
Correct Verbatim Answer
To prevent any extra drops of the solution from entering the burette, which could affect the accuracy of the initial reading.
Q.16
Why is a white paper placed under the conical flask during titration?
Correct Verbatim Answer
To clearly observe the color change of the indicator.
Q.17
Which solution is taken in the burette and which in the conical flask?
Correct Verbatim Answer
Hcl solution is taken in the burette and NaOH solution in the conical flask.
Q.18
What precautions must be taken during an acid-base titration to ensure accurate results?
Correct Verbatim Answer
•Use clean and rinsed apparatus with the appropriate solution. • Ensure no air bubbles are in the burette nozzle. • Remove the funnel before starting the titration. • Add the titrant (acid) slowly near the endpoint. Swirl the flask continuously for proper mixing. • Read the burette at eye level using an anti-parallax card. • Repeat the titration to get concordant readings.
Q.19
What is a chemistry laboratory?
Correct Verbatim Answer
A chemistry laboratory is a chemist's hop where students learn to observe physical and chemical properties of substances by following definite procedures. BASIC RADICALS
Q.20
How Chromium radical (Cr*) test can be Identified?
Correct Verbatim Answer
Add 4g sample in a clean test tube. Dissolve it in 10 cm? distilled water. Make two parts of the above solution for further tests. Experiment Observation To one part, add NaOH A green precipitate appears which solution. turns into green solution when excess of NaOH is added A green precipitate appears which To the second part of the above solution, add 1s insolúble in excess of aqueous ammonia. aqueous ammonia. Crat, + 30H (ag) → Cr (OH) 3(0)
Q.21
Discuss Identification of Ammonium (NH+ ) radical. Observation Experiment Take 4g of sample in a clean Ammonia gas is evolved with a distinct smell test tube. Dissolve it in 10cm' distilled water. Add NaOH Ammonia gas turns moist red litmus blue. solution and gently heat it.
Correct Verbatim Answer
Q.22
How Calcium (Cat) radical test can be performed?
Correct Verbatim Answer
Take 4g solid sample in a clean test tube. Dissolve it in 10cm' distilled water. Make two parts of this solution for further tests Observation Experiment To one part, add NaOH White precipitate is formed which does not dissolve in excess solution. NaOH solution. Only a slight turbidity appears or To the second part of the add above solution, No precipitate is formed. aqueous ammonia. Ca aq) + 20H (ag) → Ca (OH) 2(.) DESCRIPTIVE QUESTIONS