1. Acid – base
Q: 1 Circle only ONE correct answer:
1. The pH of a weak acid (0.1 M, Ka=10-5) =
a) 2
b) 12
c) 4
d) 5
2. While the pH of the same acid in presence of 0.0 1 N sodium acetate is :
a) 4.76
b) 5.76
c) 3.76
d) none of them
3. Used as catalyst in Kjeldahl method.
a) Na2SO4
b) CuSO4
4. The pH (effective range of indicator) =
a) pKind  1
b) pKind  10-1
c) CuNO3
c) pKind
d) NaNO3
d) pKind  log10
5. During titration of 50 ml 0.1 N acetic acid (pK a= 4.76), the pH after addition of
10 ml 0.1 N NaOH=
a) 8.73
b) 4.15
c) 12.26
d) none of the above
6. While (for the above titration) the pH after addition of 50 ml NaOH =
a) 8.73
b) 4.15
c) 12.26
d) 7
7. Indirect (residual, back) titration are used in case (s)
a) Volatile substances
c) need of certain treatment
b) insoluble substances
d) all of the above
8. is a mixture of an indicator and an inert dye whose colour does not change with pH
a) Universal indicator
c)Screened indicator
b) Mixed indicator
d) Turbidity indicator
9. Are salts of weak organic acids or bases of high molecular weight, which coagulate and
settle out of the solution at a definite pH value.
a) Universal indicator
c)Screened indicator
b) Mixed indicator
d) Turbidity indicator
10. It’s a mixture of two indicators, to produce a definite and characteristic colour
change within a very narrow range of pH
a) Universal indicator
c)Screened indicator
b) Mixed indicator
d) Turbidity indicator
11. Mixture of a number of various indicator, used for rapid and approximate
determination of pH
a) Universal indicator
c)Screened indicator
b) Mixed indicator
d) Turbidity indicator
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12. The indicator constant for methyl orange indicator can be calculated using the
following equation:
\
a) pH = pKind + log [In ]
[HIn]
c) pH = pKa + log
[A  ]
[HA]
b) pH = pKw – pKind – log
d) pH = pKw – pKb – log
[In \ ]
[OH In]
[A ]
[HA]
13. Dibasic acid can titrated stepwise with alkali provided the ratio K1/K2 is
a) 102
b) 103
c) 104
d) 10-3
14. pH if ammonium acetate solution can be calculate using the following equation
a) pH = ½ (pKw + pCs – pKb)
b) pH = ½ (pKw – pCs + pKa)
c) pH = ½ pKw + ½ pKa – ½pKb
15. For water-soluble salts the acid of which is insoluble in water, but soluble in
an immiscible solvent. For example, sodium salicylate or sodium benzoate its
determination by:
a) Formol
b) two indicators
c) Kjeldahl's
d) Biphasic
titration
method
Method
Titrations
16. Phenolphthalein in strong alkaline medium is colourless due to:
a) Has quinonoid structure
c) Has benzenoid structure
b) Tribasic salt formation
d) None of all
Q3: Formulate the balance equations represent the following reactions:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Formaldehyde with ammonium salt solution.
Hydrolysis of borax
Biphasic determination of sodium salicylate
Determination of ammonium chloride using formol titration
Reaction of sodium carbonate with HCl
Back titration of aspirin
Determination of Nitrogen by Kjeldahl's Method
Determination of Boric Acid
Determination of Carbonate and Bicarbonate in Mixture
Q 4: Write on the followings:
1. Explain the colour change of methyl orange at different pH (with drawing the
chemical structure)
2. Buffer solutions (Types, Henderson's equation for calculation the pH of buffer
solution and properties)
3. Titration of easily hydrolysable salts . Illustrate with ONE example.
4. Residual (indirect) titration (acid base titration). Illustrate with ONE example.
5. Biphasic titration
6. Double indicator titration. Illustrate one example
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7. Ostwald Theory for colour changes of acid base indicator
Q4:
Draw the structure formula of the followings:
1. Methyl orange indicator
2. I. Draw the chemical structure of phenolphthalein at different pH (mention the
type of chrmophore each time)
Q 5:
Write the equations represent the following:
1. pH for salts of weak acids and strong bases.
2. Henderson equation for acidic buffer
Q 6. Calculate:
1.
2.
3.
4.
5.
6.
Calculate the pH for 50 ml 0.1 N NH4OH solution titrated with 0.2 N HCl
standard solutions at:
a) Before titration
d) At equivalent point
b) After addition of 5 ml of titrant
e) After addition of 25.1 ml of titrant
c) At midpoint
Calculate the concentration and degree of hydrolysis for NH 4Cl salt at 5.27 pH
(Kb=1.8 x 10-5)
Calculate the pH during titration of 100 ml of 0.1 N acetic acid (pK a= 4.76) with
0.1 N sodium hydroxide
a) before the titration
c) at the equivalent point
b) after addition of 25 ml NaOH
d) after the addition of 100.1 ml NaOH
(Mention the type of equations used each time)
Calculate the pH of a solution containing 0.1 N acetic acid and 0.1 N sodium
acetate.
Compare the result if the solution contain 0.1 N acetic acid only (pKa = 4.76)
Calculate the pH of a solution containing 0.07 N ammonia and 0.28 N ammonium
chloride.
Compare the result if the solution contain 0.0 7 N ammonia only (pK b = 4.76)
Calculate the pH and the [H+] of a 0.0037M solution of cocaine base (pK b =
5.59)?
Q 7: Mark (√) for correct or (X) for false statements:
1. The Molar solution (1M) contains one gram-equivalent weight in one liter of
solvent.
2. pH of solutions of weak mono–equivalent bases; e.g. ammonia is =½ (pKw – pCa +
pKa)
3. Biphasic titration is applied for water soluble salts, their acids are water
insoluble.
4. Kjeldahl’s method can be used for determination of organic nitrogenous compounds.
5. The Normal solution (1N) contains one gram-molecular weight in one liter of
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solvent.
6. Kjeldahl’s method can be used for determination of organic nitrogenous compounds.
7. ZnO can be directly titrated with standard HCl using M.O. or M.R. as indicators.
8. M.O is the suitable indicator used for titration of weak acids versus strong bases.
Q8: How can you analyze the following?
1.
2.
3.
4.
5.
6.
7.
Mixture of Carbonate and bicarbonate
Mixtures of boric acid borax
Mixture of CaO and calcium carbonate
Mixture of hydrochloric acid and acetic acid
Sodium carbonate and sodium hydroxide
Determination of aspirin
Determination of sodium salicylate
Q9: Complete the following
1. In back titration of BaCl2 the solution must be heated to 70oC after addition of Na2CO3
to…..
2. The indicator used in titration of acetic acid with NaOH is………….. , while …………….is used in
titration of ammonium hydroxide with HCl
3. Residual or back titration is used for: (give examples)
a)
b)
c)
4. Basic buffer is consists of………and …….. such as…………. and ………..………….. and its pH=
6. The buffer capacity: ……………………………..
7. For NH4Cl salt solution the pH = …………………, while for CH3COONH4 the pH= …………………………
8. Hendrson equation for acidic buffer is ………..………., while that of basic indicator is ………………
9. Temperature has marked effect on basic buffer because: …………………………………..
10. Universal indicator is consists of ………… …………… ………………… and it is used for ………….. and ……
………
, while screened indicator is consists of ……………………………………… and is used in
…………………………….
11. In determination of of Calcium Oxide and Calcium Carbonate alcohol is added ……………….
Q10: Draw the titration curve represents the titration of:
indicator)
1.
2.
3.
4.
5.
Strong acid versus strong base.
Titration curves of Strong bases versus Strong acids:
Titration curves of weak acids versus strong bases
Titration curves of weak bases versus strong acids
Carbonate and Bicarbonate in mixture versus HCl
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(mention the suitable
2. Volumetric Precipitation Titration
Q: 1 Circle only ONE correct answer:
1. The Ksp for the SrF2 (its solubility = 0.114 g/L, and M.W. 126) =
a) 9.05x 10-4
b) 3 x 10-9
c) 1.5 x 10-32
d) 1.1 x 10-10
2. Which of the following compounds decrease the solubility of BaSO4:
a) MgCl
b)NaNO3
c) NaSO4
d) non of the above
3. Which of the following indicator cannot be used in precipitimetric determination of Cl a) Rodamine
b) eosin
c) fluorescein d) none of the above
4. Using Mohar method for determination of halides the pH of the medium must be:
a) >10
b) <6
c) in between 6 -10
d) non of the above
5. Used as precipitating agent in determination Ba2+:
a) potassium ferrocyanide
c) sodium pyriantimonate
b) sodium rhodizonate
d) Rhodamine
Q2: Formulate the balance equations represent the following reactions:
1) Liebeg’s method for determination of cyanide
2) In Denige's modification of Liebig method
Q 3: Write on the followings:
1.
2.
3.
4.
Q4:
Limitation of Mohr's method (illustrate by equations)
Fajan’s method for determination of chloride
Mohr method (formation the second precipitate)
Volhard’s method for Cl- determination
Draw the structure formula of the followings:
1. Barium rodizonate
2. Eriochrome Black T (EBT)
3.
Fluorescein
Q 5. Solve the following problems:
1. Calculate the solubility of Mg(OH)2 in pure water (Ksp =3.4 x 10-11, M.wt 58)
2. Calculate the solubility product of lead phosphate pb3(PO4)2 (solubility 0.00014
g/liter and M.wt=811.7)
3. Calculate of the solubility of silver chromate from its solubility product K sp = 24 x
10–12, MW =331.8
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4. Calculate the solubility product of strontium fluoride SrF2 (solubility 0.114 g/liter and
M.Wt = 126)
5. Calculate the solubility of AgCl in pure water (Ksp = 1.1 x 10-10, M.Wt. 143)
Q6: Mark (√) for correct or (X) for false statements:
1. Mohr’s method is not recommended for iodide – determination.
2. Volhard method is based on the titration of silver ion with standard
thiocyyanate.
3. Arsenate, phosphate and oxalate interfere in the determination of chloride by
Volhard’s method.
4. Mohr's method is not recommented for iodide determination of Cl5. In Fajan's method eosin is the best indicator for determination of Cl6. The presence of diverse ion decrease the solubility of slightly soluble compound
3. Gravimetry
Q1: Write short notes on:
1)
2)
3)
4)
5)
6)
Homogeneous precipitation (give examples)
Pyrolysis curves for calcium oxalate
Types of contamination
Removal of contamination in gravimetric analysis
Organic precipitant
Determination of Cl- (or sulphate, aluminum., iron , magnesium, calcium)
gravimetry
Q6: calculate:
Orthophosphate (PO43-) is determined by weighting as ammonium phosphomolybdate,
(NH4)3PO4.12MoO3. Calculate the percent of P in. the sample and the percent of P2O5 if the
precipitate from a 0.2711-g sample weighed 1.1682g.
Q7: Mark (√) for correct or (X) for false statements:
1) Drying is ususally done at temoperature above 250 o C while ignition below that
temperature
2) The graph recording the volume of titrant against pCs is called pyrolysis curves
3) Washing a precipitate is useful to remove surface adsorbed impurities
4) Organic precipitats are more sensitive and can be used for determination of minute
amount of ions
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