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Example: Methyl orange, Phenolphthalein, Methyl red, Methyl blue. Colour in alkaline media(base)

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JHARKHAND RAI UNIVERSITY LAB MANUAL of B.Tech –I semester 1. Study of indicator (methyl orange)

Theory:indicators are generally weak organic compound which have different colour in different media. It is used in volumetric analysis where change of colour indicate the end point of the reaction .the change of colour also indicates whether the solution is acidic , base , or neutral. An indicator does not take part in a chemical reaction but it change in colour raptly on the neutral point or equivalence.

Example: Methyl orange, Phenolphthalein, Methyl red, Methyl blue Colour change of indicator in different media

Indicator Colour in alkaline media(Base) Colour in neutral media Colour in Acidic media

Methyl orange Yellow Orange pink

Phenolphthalein pink colourless colourless

Selection of indicator

Titrating of Indicator used

Acid Base

Strong(HCL,H2SO4,HNO3) Strong(NaOH,KOH) Use any indicator

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Weak (oxalic acid ,acetic acid) Strong Phenolphthalein

Weak Weak No indicator is

suitable, do not titrate.

Chemical required:

(i) NaOH (N/10) solution (ii) HCl (N/10) solution (iii) Methyl orange Apparatus required

(i) Burette stand (ii) Burette

(iii) Pipette (iv) Beaker

(v) Conical flask (vi) Conical funnel (vii) Dropper

Procedure:

(a) Take a burette and wash it with distilled water.

(b) Rinse and fill the solutionHCl N/10 with the help of conical funnel and set the initial burette reading as zero.

© Clamp it vertically to the burette stand.

(c) Rinse the pipette with water and then with the given NaOH solution. (d) Pipette out 10ml of given NaOH (N/10) solution into a conical flask

and add one or two drops of methyl orange.

(e) Titrate it against the HCl(N/10) solution taken in the burette till the colour of the solution in the conical flask changes from colour yellowish to pink colour

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(g) Repeat the titration until concordant values are obtained. Observation: No of observation Volume of NaOH solution in mL Burette reading

Different Constant Indicator used Initial Final

Calculation:

2. Determination of strength of KMnO4 using standard solution of Mohr's salt

Theory:

In this titration, potassium permanganate is the oxidizing agent and Mohr’s salt is the reducing agent. Mohr’s salt is a double salt of ferrous sulphate and ammonium sulphate and its composition is FeSO4.(NH4)2SO4.6H2O. It is a

primary standard. Therefore, its standard solution can be prepared directly. Ferrous ions of Mohr’s salt undergo hydrolysis in aqueous solution. To prevent the hydrolysis, Conc. H2SO4 needs to be added to the Mohr’s salt

crystals during the preparation of its standard solution. Chemical required:

(i) Potassium permanganate (KMnO4) (ii) Mohr’s salt (FeSO4.(NH4)2SO4.6H2O)

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Apparatus required

(viii) Burette stand (ix) Burette

(x) Pipette (xi) Beaker

(xii) Conical flask (xiii) Conical funnel (xiv) Dropper

(xv) Measuring flask 10mL. Procedure:

(a)

Take a burette and wash it with distilled water.

(b)

Rinse and fill the solution KMnO4 with the help of conical funnel and set the initial burette reading as zero.

(c)

Clamp it vertically to the burette stands.

(d)

Rinse the pipette or measuring flask with water and then with the given solution.

(e)

Pipette out or measure 10ml of given Mohr’s salt solution into a conical flask and add half test tube of H2SO4 solution

(f)

Titrate it against the KMnO4 solution taken in the burette till the colour of the solution in the conical flask changes from colourless to light pinkcolour.

(g)

Note down the final burette reading.

(h) Repeat the titration until concordant values are obtained. Observation: No of observation Volume of NaOH solution in mL Burette reading

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Calculation:

3. Estimation of Hydrochloric Acid solution Supplied titrating against standard Sodium Hydroxide Solution

Objective: — the main theme of this experiment is to determine the strength of ‘Commercial Hydrochloric acid’ with a standard Sodium Hydroxide

solution. As Sodium Hydroxide is itself a secondary standard substance, so it is standardized by the standard Oxalic-acid solution.

Theory: — in this experiment we shall determine the Strength of commercial Hydrochloric Acid solution by a secondary standard solution of NaOH. This is done by means of ‘Titration’. The important matters that are related with the experiment are stated below:

Titration: — in presence of a suitable indicator, the volumetric analysis in which a standard solution is added in another solution (whose strength is not known) to reach its end point to determine the strength of that solution is called ‘titration’.

Standard Solution:A solution of known concentration is called a ‘standard solution’.

Secondary Standard Solution: — A ‘Secondary Standard’ is a substance which may be used for standardizations, and whose content of active

substance has been found by comparison against a primary standard. On the other hand ‘primary standard’ is a compound of sufficient purity from which a standard solution can be prepared by direct weighing of a quantity if it, followed by dilution to give a defined volume of solution.

Indicator: — in our acid-base titration there is an important use of indicator. An ‘indicator’ is a chemical substance that detects the Equivalent point (i.e. the end point) of reaction by changing its colour. Indicators have different structures in acidic and in basic solution.

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The ‘equivalent point’ is the point in a titration when a stoichiometric amount of reactant has been added.

Normality: The number of gram equivalent weight of a solute per liter of solution is called normality.

Normality (N) = gm. equivalent of solute /liters per solution. It is known to us that both alkalimetry and acidimetry are based on neutralization reaction.

Acid produces H+ and alkali produces OH-ions (Hydrogen and Hydroxyl ion respectively) and when they come in contact with each other, they create H2O (water) by combining with one another.

H+ + OH- =H2O

It is the basic concept of neutralization and by using this idea a certain volume of standard solution is allowed to react with a known volume of another solution until neutral point is achieved. Some chemical reagents called indicators are used to determine the neutral point.

If an acid-base reaction is such like that, aACID + b BASE = PRODUCT

Then we know that

V base X S base= V acid X S acid So, S acid = (V base X S base) / V acid

As NaOH is a secondary substance it will be first standardized using primary standard substance ‘Oxalic-acid’

Chemical required:

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Apparatus required

(xvi) Burette stand (xvii) Burette

(xviii) Pipette (xix) Beaker

(xx) Conical flask (xxi) Conical funnel (xxii) Dropper

Procedure:

(a) Take a burette and wash it with distilled water.

(i) Rinse and fill the solution HCl N/10 with the help of conical funnel and set the initial burette reading as zero.

© Clamp it vertically to the burette stand.

(j) Rinse the pipette with water and then with the given NaOH solution. (k) Pipette out 10ml of given NaOH (N/10) solution into a conical flask

and add one or two drops of methyl orange.

(l) Titrate it against the HCl(N/10) solution taken in the burette till the colour of the solution in the conical flask changes from colour yellowish to pink colour

(m) Note down the final burette reading.

(n) Repeat the titration until concordant values are obtained. Observation: No of observation Volume of NaOH solution in mL Burette reading

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Calculation:

4. Estimation of NaOH solution Titrating against(N/10) Oxalic acid solution.

Theory:

Estimation means to determine the amount of the substance in gram present in 1L of its solution

Gram per liter = equivalent wt. X Normality of solution Where normality is determine from the relation.

N1V1=N2V2

Chemical required:

(vii) NaOH (N/10) solution (viii) Oxalic (N/10) solution (ix) Phenolphthalein

Apparatus required

(xxiii) Burette stand (xxiv) Burette

(xxv) Pipette (xxvi) Beaker

(xxvii) Conical flask (xxviii) Conical funnel (xxix) Dropper

Procedure:

(a) Take a burette and wash it with distilled water.

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© Clamp it vertically to the burette stand.

(p) Rinse the pipette with water and then with the given NaOH solution. (q) Pipette out 10ml of given NaOH (N/10) solution into a conical flask

and add one or two drops of methyl orange.

(r) Titrate it against the oxalic acid (N/10) solution taken in the burette till the colour of the solution in the conical flask changes from pink colour tocolourless.

(s) Note down the final burette reading.

(t) Repeat the titration until concordant values are obtained.

Observation: No of observation Volume of NaOH solution in mL Burette reading

Different Constant Indicator used Initial Final

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5. Preparation of potass alum Theory:

Crystallization is always carried out with saturated solution .potass alum in the commercial name its chemical name is potassium sulphate aluminum sulphate 24.H2O [K2SO4.Al2(SO4)3.24H2O] Chemical required: (i) K2SO4O (ii) Al2(SO4)3 Apparatus required

(i) Copper water bath (ii) China Basin

(iii) Glass rod (iv) Beaker (v) Spatula (vi) Watch glass (vii) Tripod (viii) Filter paper

Procedure:

1. I g of K2SO4was dissolve in minimum volume of

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2. 2g of Al2(SO4)3 was dissolve with similar fashion in another 100mL

beaker.

3. The two solutions mixed together and taken in basin and evaporate on the cupper water bath.

4. When crystal appeared on the solution the basin was made float on water taken in a beaker up to it top. It was cooled at the room temperature.

5. The mother liquor was decanted out and crystal were press between layer of filter paper to soak dry

6. Salt analysis :

Group I (dilute H2SO4 group) –CO32-(carbonate), SO32- (sulphite), S 2-(sulphide), NO2- (nitrite): Salt + dilH2SO4

1. No reaction: Group I anion notpresent. Continue to group II. 2. Carbonate: Colourless andodorless gas (CO2)

1. WE 1 + MgSO4 = white ppt

3. Sulphite: Colourless gas withpungent smell

1. WE + BaCl2 (aq) = white ppt soluble in dilHCl

Group II (conc H2SO4 group) –Cl-(chloride), Br- (bromide), I- (iodide), NO3- (nitrate), CH3COO- (acetate), C2O42-(oxalate): Salt + conc H2SO4

1. No reaction: Group II anion notpresent. Continue to group III.

2. Chloride: Colourless whitepungent fumes (HCl); intensify when glass rod dipped in NH4OH is brought near mouth of test tube

1. Silver nitrate test: WE +AgNO3 = white ppt soluble in NH4OH 2. Chromyl chloride test: Salt +solid K2Cr2O7 + 2-3 drops conc

H2SO4 = orange / red fumes of chromyl chloride 6 1. Vapours + NaOH (aq) = yellow solution

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3. Bromide: Reddish brown vapour

1. Silver nitrate test: WE +AgNO3 (aq) = yellow ppt partially soluble in NH4OH

2. Organic layer test: WE + CCl4+1 drop conc HNO3 = Upper layer aqueous; lower layer organic of orange / brown colour (bromine is soluble in non-polar solvent)

4. Iodide: Violet vapours

1. Silver nitrate test: WE +AgNO3 (aq) = yellow ppt insoluble in NH4OH

2. Organic layer test: WE + CCl4 + 1 drop conc HNO3 = Upper layer aqueous; lower layer organic of violet colour (iodine is soluble in non-polar solvent)

5. Nitrate: Brown fumes withpungent smell, which intensify on adding paper pellets (may need heating)

1. Brown ring test: WE + freshlyprepared FeSO4 sol + 1 drop conc

HNO3 added alongside of test tube = brown ring formed at junction of sol and acid

Group III anions (special group) –

SO42- (sulphate), PO43- (phosphate): Nogroup reagent

1. Sulphate:

1. Barium chloride test: WE +BaCl2 (aq) = white ppt insoluble in concHCl

2. Lead acetate test: WE + leadacetate (aq) + acetic acid = white ppt soluble in CH3COONH (ammonium acetate)

Cations

Group 0 –NH4+(ammonium):Nogroup reagent

1. Sodium hydroxide test: Salt +NaOH = pungent smelling gas; gives white fumes when a glass rod dipped in concHCl is brought near mouth of test tube

2. Nessler's reagent 8 test: OS9+NaOH + Nessler's reagent = Brown / yellow ppt

Group I –Pb2+(lead):

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1. Leave OS undisturbed = white crystals formed on cooling 2. Potassium iodide test: OS + KI =yellow ppt

3. Potassium chromate test: OS +K2CrO4 = yellow ppt

Group II –Cu2+(copper): OS + dilHCl + H2S = black ppt

1. Throw off extra sol, retain ppt, and dissolve in a few drops of conc HNO3 = bluish green sol, ppt dissolves; divide into two parts 1. Part 1 + excess NH4OH = blue coloured sol

2. Potassium ferrocyanide test:

Part 2 + acetic acid + K4[Fe(CN)6] = reddish brown / chocolate colouredppt (Note – this test is difficult to get)

Group III –Fe2+, Fe3+(iron), Al3+(aluminium):

OS + solid NH4Cl + excess NH4OH

1. Fe2+ / Fe3+: Note – ferrous saltsare green in colour, ferric salts are brown in colour.

1. If ferrous salt has been given, convert to ferric: OS + concHNO3 + heat = brown ppt; then do reaction with group reagent

2. Brown ppt + HCl; then divide into two parts

1. Potassium ferrocyanide test: Part 1 + K4[Fe(CN)6] =blue ppt / colour

2. Potassium thiocyanate test: Part 2 + KCNS = bloodred colour 2. Al3+: Gelatinous white ppt

1. Blue lake test: Retain ppt + dilHCl = clear sol

1. Sol + blue litmus and NH4OH (drop-by-drop) = blue colour layer ('lake') floats over colourless sol

Group IV –Co2+(cobalt), Ni2+(nickel),Mn2+ (manganese), Zn2+ (zinc):

OS + solid NH4Cl + excess NH4OH + pass H2S gas

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1. Co2+: Blue residue; turnspink / purple when dissolved in water; divide into two parts

1. Part 1 + dil acetic acid + KNO2 + warm = yellow ppt

2. Part 2 + ether (1 mL) + solid NH4CNS 11 = blue colour in ether

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References

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