IX Practical Chemistry KBSE Experiment No. 6

To Neutralize an acid (Hydrochloric Acid) with base (Sodium Hydroxide)using Phenolphthalein as indicator.

Viva Voce
Q.1. What is an Acid?

Ans. Acids are compounds whose solution in water exhibit the following properties.

1. They have a sour taste.

2. They turn blue litmus red.

3. They give hydrogen when treated with metal.

4. They react with metal oxides and their hydroxides forming salt oxide and water.


Q.2. What is Arhenius definition of an Acid?

Ans. According to Arhenius. Acids are those substances which produce H ions in aqueous

solution.


Q.3. What is Ionization?

Ans. The process of formation of H ions from acids is known Ionization.


Q.4. What are Strong Acids?

Ans. Those acids which ionize completely are called Strong Acids. Examples HCl, H2SO4, HNO3.


Q.5. What are Weak Acids?

Ans. Acids which ionise to small extent in water are called Weak Acids.


Q.6. What are Hydronium Ions?

Ans. Free H ions do not exist freely in water and so they are associated with water and form

H3O (Hydronium Ions)


Q.7. What is Lowry and Bronsted definition of Acid?

Ans. Lowry and Bronsted defined an acid as a substance which tends to lose Protons or Acids

are Protons Donors.


Q.8. What is Lewis definition of an Acid?

Ans. It has been observed that donation of Hydrogen Ion in an acid is not essential, since

an acid may not even possess as Hydrogen atom in its molecule. Hence Lewis an American

Scientist proposed generalised concept of acid. Acid is an electron acceptor.

Example. Aluminium Chloride acts as Lewis Acid because its molecule is short of two

electron.


Q.9. In which substances do the following acids occur? Citric Acid, Tartaric Acid, Acetic

Acid, Lactic Acid, Formic Acid.

Ans.

Citric Acid -------> Lemon

Tartaric Acid -----> Grapes, Tamarind

Acetic Acid -------> Vinegar

Lactic Acid -------> Fermented milk

Formic Acid -------> Sting of bees, Wasp


Q.10. What is the effect of Acid on the following? Blue Litmus, Methyl Orange,

Phenolphtalene.

Ans.

Blue Litmus -------> Red

Methyl Orange -----> Red

Phenolphtalene ----> No effect.


Q.11. What happen when acid reacts with base?

Ans. Acids and Bases neutralize each other then salt and water are formed.

Hcl + NaOH -------> NaCl + H2O

(Acid) (Base) (salt) (Water)


Q.12. What is Basicity of Acid?

Ans. The number of replaceable or ionizable Hydrogen atoms present in the molecule of Acid

indicates its Basicity. Example

HCl -------> Monobasic Acid

H2SO4 -----> Dibasic Acid

H3PO4 -----> Tribasic Acid


Q.13. What is Concentrated Acid?

Ans. Pure Acid containing no water is called Concentrated Acid.


Q.14. What is Dilute Acid?

Ans. Acid containing large amount of water is called Dilute Acid.


Q.15. Does the acid react with Gold and Silver?

Ans. No.


Q.16. What is the effect of acid on the Skin?

Ans. Strong Acids Corrode the Skin.


Q.17. What is the percentage of HCl in the gastric juice?

Ans. 0.2 to 0.4%


Q.18. What is the function of HCl in the Human Body?

Ans. It is essential for the proper digestion of food.


Q.19. What is the definition of Base according to Arhenius?

Ans. According to Arhenius a base is a substance which in aqueous solution provides Hydroxyl

Ions (OH) Example NaOH, Ba(OH)2, Al(OH)3

NaoH <-------> Na+ + OH

Ba(OH)2 <-------> Ba++ + 2OH-

Al (OH)3 <-------> Al+++ + 3 OH-

Q.20 What is the definition of base according to Lowry and Bronsted?

Ans. A base is a proton acceptor.




Q.21. Is it essential that an acid should donate H+ ions?

Ans. Donation of Hydrogen ions in an acid is not essential since an acid may not even

possess a Hydrogen Atom in its molecule.




Q.22. What is generalised definition of Base according to Lewis?

Ans. Base is an electron donor.




Q.23. What are the general properties of Base?


Ans.


1. They have a bitter taste.


2. They have slippery touch.


3. They conduct electricity.


4. They react with indicators


Red Litmus -------> Blue


Phenolphtalene ---> Pink


Methyle Orange ---> Yellow


Turmeric Paper ---> Brown


5. Combine with fats to form Soaps.


6. They react with bases to form salt and water.


NaOH + HCl -------> NaCl + H2O




Q.24. What is Strong Base?

Ans. A base which ionises completely is called Strong Base e.g. NaOH, KOH.


Q.25. What is Weak Base?

Ans. A base which contain small amount of water is called Weak Base.


Q.26. What is Concentrated Base?

Ans. A base which contains small amount of water is called Concentrated Base.


Q.27. What is Dilute Base?

Ans. That base which contain large amount of water is called Dilute Base.


Q.28. What is an Alkali?

Ans. A base which is highly soluble in water is called an Alkali. It ionises nearly

completely e.g. NaOH, KOH.


Q.29. Do you think that every base is an Alkali?

Ans. No.


Q,30. Do you think Alkali is a base?

Ans. Yes.


Q.31. What is the Acidity of Base?

Ans. The number of Hydroxyl Ions which a molecule of base can provide is called Acidity of

the base.

NaOH -------> Monoacid Base

Ba(OH)2 ----> Diacid Base

Al(OH)3 ----> Triacid Base


Q.32. Give examples of Weak Acids?

Ans. Acetic Acid (CH3COOH), Carbonic Acid (H2CO3).


Q.33. Does Acetic Acid ionise completely?

Ans. No. it ionises partially.


Q.34. Give example of Weak Base?

Ans. NH4OH (Ammonium Hydroxide)


Q.35. What is One Mole?

Ans. Molecular Weights of a substance in gram is termed 1 Mole.


Q.36. By how much amount of base, one mole of acid can be neutralised?

Ans. One Mole of Base is required.


Q.37. What is Neutralization?

Ans. Neutralization is simply a reaction between Hydrogen Ion of an Acid an Hydroxide Ion of

the base to form water. In this reaction salt is also produced which remains in the solution

as Ion.


Q.38. What is meant by "Titraton"

Ans. Titration is the process of adding one solution from Burette in the conical flask (or

any other container containing known volume of other solution) to measure the volume of the

solution of the burette after the completion of chemical reaction between the two solutions

using indicator.

OR

Titation is the process of adding one solution from one burette to another in the conical

flask in order to determine its volume after the completion of Chemical reaction.

OR

Titration is an operation by which the strength of an unknown solution is determined by

allowing it to react with a standard solution.


Q.39. Why do you use Phenolpthalene as indicator in the experiment?

Ans. This is a titration of weak acid and a strong base. Hence Phenolphtalene is a suitable

indicator.


Q.40. What do you mean by End Point?

Ans. It is the exact stage at which the chemical reaction of the titration solutions is just

completed.


Q.41. Why alkali is taken in the burette when Phenolphtalene is used as an indicator?

Ans. The appearance of a pink colour at the end point can be observed easily. So it is

comparatively better than the disapperance of colour when acid is used in the burette.


Q.42. What are the Ionic definitions of Acids and Bases?

Ans. By the ionic point of view the acids are substances which give Hydrogen Ion (H+) in

solution while bases are substances which give Hydroxyl Ion (OH-) in solution.


Q.43. What is the formula of Oxalic Acid?

Ans. The formula of Oxalic Acid is

COOH

|

COOH


Q.44. What substances are present in the conical flask after neutralization?

Ans. Salt and water are present in the conical flask after neutralization.


Q.45. How will you obtain salt from the conical flask?

Ans. Salt can be obtained by evaporation.


Q.46. What do you undertand by the words 10 ml and 20oC written on the pipette?

Ans. It means that 20oC temperature, the pipette can contain 10 ml of liquid upto the given

mark.


Q.47. How will you represent the reaction of Oxalic Acid with Sodium Hydroxide by

Chemical equation?

Ans.

COOH COONa

| + 2NaOH ----> | +2H2O

COOH COONa


(oxalic acid) (Sodium Hydroxide) (Sodium Formate) (Water)


Q.48. What is an Indicator?

Ans. Indicator is a substance which is added to the solution in titration process and

indicates the end point of the reaction.


Q.49. Why do you call Oxalic Acid an Acid?

Ans. Oxalic Acid is called Acid because in its aqueous solution, it gives of H+ ions and it,

turn blue litmus red.


Q.50. What is the reaction between Sodium Hydroxide and Hydrochloric Acid?

Ans.

NaOH + HCl ----------> NaCl + H2O

(SOdium Hydroxide) (Hydrochloric Acid) (Sodium Chloride) (Water)


Q.51. What are the two important indicators generally used in titration?

Ans. Phenolphtalene and Methyl Orange are the two indicators generally used in Titration.


Q.52. How many number of molecules are present in the Crystals of Oxalic Acid?

Ans. Two molecules of water are present in the crystal of Oxalic Acid (C2H2O4.2H2O)


Q.53. What name is given to the water molecules present in the Crystals of a Solid

Substance?

Ans. Water molecules of Crystallisation.


Q.54. What is the formula of Sodium Carbonate?

Ans. Na2CO3.


Q.55. What is meant by weak Alkali?

Ans. A weak alkali is that alkali which does not ionise completely and produces less number

of Hydroxyl group.


Q.56. Give the names of few Alkalies?

Ans.

1. Calcium Hydroxide

2. Barium Hydroxide

3. Sodium Carbonate

4. Sodium Bicarbonate

5. Potassium Bicarbonate


Q.57. What indicator is used in the titration between strong acid and weak alkali?

Ans. Methyl orange indicator is used between the titration of strong acid and weak alkali.


Q.58. What is the colour of Methyl orange in Acid and in Alkali?

Ans. Methyl orange gives reddish colour in acidic medium while yellow in alkaline solution.


Q.59. Give structural formula for Methyl Orange?

Ans. Methyl Orange is an Azodye. Its structural formula is given below.

______ _______
/ \ / \

SO3H \______/ N=N \_______/ N(CH3)2


Q.60. What is Litmus?

Ans. It is well known indicator for acids and alkalies. It is derivative of arcinol. It is

also extracted from Lichens.


Q.61. What is Phenolphtalene?

Ans. It is an indicator used in titration. It is prepared by heating to 120oC Phthalic

Anhydride and Phenol for about 8 hours in presence of Anhydrous ZnCl2 or Cone.H2SO4.


Q.62. Give the names of some salts?

Ans. Sodium Carbonate (Na2CO2) Sodium Chloride (NaCl) Potassium Chloride (KCl) Magnesium

Sulphate (MgSO4)


Q.63. What are the necassary precautions in this experiment?

Ans.

1. Burette and Pipette should be washed and rinsed.

2. Burette should be clamped in the stand vertically.

3. While taking reading in the burette lower meniscus should be read.

4. There should be no air bubble in the solution in burette.


Q.64. What is Standard Solution?

Ans. A solution of known strength is called a Standard Solution.


Q.65. What is a Normal Solution?

Ans. A solution containing 1 gm equivalent weight of the substance dissolved per litre of

the solvent is called a normal solution e.g. NOrmal Solution of NaOH contains 40 gm of it

dissolved in 1 litre of water.


Q.66. How can you get salt from conical flask?

Ans. We can get salt from the conical flask by the process of Evaporation.


Q.67. Why Methyl orange is used in the Titration?

Ans. It is an indicator (Complex organic compound) used in the titration of a weak base and

strong acid.


Q.68. What is a Pipette?

Ans. It has a cylindrical shape made up of a glass for measuring the volume of a liquid. It

is marked upto 10 ml to 20 ml


Q.69. What is a Burette?

Ans. It has a cylindrical shape made up of a glass used for measuring the volume of a

liquid. It is marked from 0 ml to 50 ml or 100 ml.


Q.70. While handling the burette what precautions are necassary to be observed?

Ans.

1. Burette should be clamped vertically

2. Lower meniscus of liquid layer should be noted.

3. Remove the air bubbles before starting experiment.

4. Fill it with the help of funnel.


Q.71. What is Pilot Reading?

Ans. The first reading which is obtained after end point.


Q..72. What do you mean by "End Point"?

Ans. That stage at which the Chemical reaction of titration solution just complete.


Q.73. What is Litmus Dye or Litmus Paper?

Ans. It is a dye or Organic compound which is obtained from a plant and which is used as an

indicator as it turns red with acid and red litmus turns blue with base.


Q.74. How do we rinse the burette?

Ans. Wash the burette with water and afterwards rinse with the solution which will be poured

in it.


Q.75. How do you decide that Neutralization is complete?

Ans. Neutrazilation is complete when the single drop of NaOH (Sodium Hydroxide) is added due

to which pink colour is formed.


Q.76. When will you use Methyl Orange as indicator?

Ans. Methyl Orange is used as an indicator for the titration of Strong Acid and Weak Alkali.


Q.77. How is the end point indicated?

Ans. It is indicated by light pink colour.


Q.78. What does light pink colour indicate?

Ans. It shows that neutralization is complete.


Q.79. How do you take the last drop of acid from the Pipette?

Ans. We close the open end of the Pipette with the finger and hold the bulb in the hand,

then the air in the bulb expands due to heat of the hand and forces the last drop out.


Q.80. Which meniscus will you note while taking down the reading of the burette?

Ans. The Lower meniscus.


Q.81. Why do you note lower meniscus?

Ans. In case of colourless liquid lower meniscus is noted and in case of coloured liquid

upper meniscus is noted.


Q.82. How should we read the graduations?

Ans. We put on a piece of white paper on the opposite side so that level of liquid is easily

visible.


Q.83. Which indicator will be used for titration in the following cases?

1. Weak Acid against Strong Alkali

2. Strong Acid against Weak Alkali

3. Strong Acid againts Strong Alkali


Ans.

1. Weak Acid and Strong Base -------> Phenolphtalene

2. Strong Acid and Weak Base -------> Methyl Orange

3. Strong Acid and Strong Base -----> Phenolphtalene or Methyl Orange


Q.84. What are the conditions for a substance to be used as an indicator?

Ans.

1. It should not effect the chemical action.

2. It should give characteristics colour with one of the ions taking part in the chemical

acton.

3. A few drops of it should produce the characteristic change in colour.