Exp-12.1: To Analyse the Given Salt for Acidic and Basic Radicals

Analytical chemistry is the chemical analysis of a particular compound, which includes both qualitative and quantitative analysis of a substance. Qualitative analysis of inorganic salts is a process of detection of acidic and basic radicals present in a given salt. Inorganic salts are obtained through the complete or partial neutralisation of an acid and base.

Table of Contents

• Aim 

• Apparatus Required

• Theory: Dry Heating Test

• Procedure

• Observation

• Result

Aim

To analyse the given salt for acidic and basic radicals using a dry heating test.

Apparatus required

1. Test tubes

2. Test tube holder

3. Salt sample

4. Bunsen burner

Theory

1. Qualitative analysis of various inorganic salts is based on two basic principles, i.e. Solubility of a product and the Common ion effect. 

2. Solubility product is defined as the equilibrium present between a solid compound and its ions in a solution. Hence, when the ionic product of a salt exceeds the solubility product, precipitation of that particular ion takes place. 

3. The common ion effect is what controls the ionic products of various salts. It is known to suppress the ionisation of a particular electrolyte when another electrolyte having a common ion is added to the solution. 

4. Dry heating is a test which is used to detect anions and cations of a particular salt. The heating of salts causes them to undergo decomposition which leads to the release of a particular gas, or it may show a significant colour change in the residue.

Procedure

1. Take 0.1g of dry salt in a properly dry and clean test tube.

2. Heat the contents of the test tube over a Bunsen burner for about one minute.

3. Observe the changes occurring in the test tube.  

4. Note down the observations.

Dry heating test

Observations 

Result

To identify the acid and basic radicals in the given sample, a dry heating test is conducted, and it will help to identify nitrate, halides, copper, ferrous, zinc and cobalt ions. 

Precautions

1. Use a completely dry test tube for the above test, not even a drop of water should be present.

2. While heating the test tube, do not heat it constantly, but keep it over an angle and heat it slowly by removing it to and fro from the flame.

3. Keep the test tube away from the mouth, nose and body.

4. Use all lab safety gadgets such as lab coats and hand gloves.

5. Use a proper, stable test tube holder to heat the test tube.

Lab Manual Questions

1. What are the basic steps involved in inorganic salt analysis?

Ans: For a systematic analysis of a given inorganic salt, the following steps are performed:-

• Preliminary tests are conducted for the given salt. These are generally dry tests and hence use the powdered or dry form of the salt.

• Determination of cations is conducted using a wet test followed by confirmatory tests for the derived action. 

• Determination of anions is conducted using a wet test, followed by confirmatory tests for the derived anion.

• Both of the wet tests are conducted by using the solution of the salt.

2. What does a physical examination of salt mean?

Ans: Physical examination of salt is the study of the given salt for its colour, smell, density etc. This basic information helps us understand which ions might be present or absent in the given salt. E.g. If the colour of the salt is white then there is a possibility that the salt does not contain Cu2+, Mn2+, Co2+, Fe3+ etc ions. 

3. What is a flame test?

Ans: Salts when reacted upon by conc. HCl from chlorides, which are volatile and their vapours, impart distinctive colour to the flame. In a flame test, a paste of salt and conc. HCl is prepared. With the help of a platinum wire, this salt paste is introduced in the non-luminous flame and colour change is observed. This test can determine the presence of some basic radicals such as Sr2+, Ba2+, Ca2+ etc.

4. What is aqua-regia?

Ans: Aqua-regia is a mixture of concentrated HCl and concentrated HNO3. It is prepared in a ratio of 3:1 and is used for dissolving salts which are insoluble in water, dil HCl and dil HNO3. A salt which does not dissolve in aqua regia is also termed an insoluble salt.

Viva Questions 

1. How is O.S. made?

Ans: O.S is known as the original solution and is prepared by dissolving a small amount of the given salt into either water, dil HCl, dil HNO3 or aqua regia.

2. Give the uses of table salt.

Ans: Table salt is majorly used for flavouring food items and the preservation of food items. It is also used for tanning, dyeing, bleaching, etc.

3. Define normal salts.

Ans: Salts which are formed by the complete replacement of the ionizable H+ ions or OH- ions by metallic ions of a base are known as normal salts. E.g.- HCl reacts with NaOH giving NaCl and water. 

4. Enlist the members present in group 4 basic radicals.

Ans: Group 4 of the basic radicals contain- Co2+, Mn2+, Ni2+, Zn2+

5. What does a radical group mean?

Ans: Radicals are also known as free radicals, and these are molecules which contain at least one unpaired electron. 

6. Give the group reagent used for the detection of group 4 cations.

Ans: The group reagent for Group 4 cations is Hydrogen sulphide(H2S)  in the presence of Ammonium hydroxide(NH4OH).

7. What are acids and bases?

Ans: Acid is a substance which is sour and turns blue litmus paper red. For, e.g.- HCl, and HNO3. The base is soapy and bitter to taste and turns red litmus paper blue. E.g.- NaOH, KOH, Ca(OH)2 etc.

8. How is salt formed?

Ans: Salt is formed due to the neutralisation reaction between an acid and base, and hence it generally has a neutral pH.

9. What is the general scale of acids and bases on a pH scale?

Ans: Acids have a pH range of 0-6 and bases have a pH range of 8-14. The pH 7 is for neutral compounds.

10. What is a double salt?

Ans: A salt formed by the crystallisation of two simple salts or from a mixture of their respective saturated salt solutions is known as double salt. E.g. Potash alum.

Practical Based Questions (MCQs)

1. Find the odd one out

1. Flame test

2. Borax bead test

3. Charcoal cavity test

4. Basic radicals group-III tests

Ans: Basic radicals group-III tests

2. Non-luminous flames are also known as____

1. Oxidising flame

2. Reducing flame

3. Medium flame

4. Green colour flame

Ans: Oxidising flame

3. The original solution is used for

1. Dry tests

2. Flame tests

3. Wet tests

4. Colour test

Ans: Wet tests

4. In salt analysis, cation is _____and anion is_____

1. Acidic radical, basic radical

2. Basic radical, acidic radical

3. Negative, positive

4. Both A and C

Ans: Basic radical, acidic radical

5. A salt which is formed from the partial replacement of hydroxyl groups from a polyacidic base by an acidic radical is a ____

1. Acidic salts

2. Basic salts

3. Normal salts

4. Mixed salt

Ans: Basic salt

6. A basic radicals list includes

1. Sodium, Ferrous, Gold, and Nickel ions

2. Sodium, Chlorine, Potassium, and Aluminium ions

3. Ferrous, Sulphate, Cobalt, and Mercury ions

4. Nitrate, Nitrite, Helium, and Chromium ions

Ans: Sodium, Ferrous, Gold, Nickel ions

7. Mention the group reagent of group I of cations

1. Dil sulphuric acid 

2. Dil hydrochloric acid

3. Ammonium hydroxide

4. Hydrogen sulphide

Ans: Dil hydrochloric acid

8. Group III of cations contains___and ____

1. Magnesium ions, calcium ions

2. Lead ions, Copper ions

3. Magnesium ions, aluminium ions

4. Ferric ions, aluminium ions

Ans: Ferric ions, aluminium ions

9. Assertion: Acidic radical is negative in charge

Reason 1: It is formed due to the release of a negative charge from a base.

Reason 2: It is formed due to the release of hydrogen ions from an acid.

1. Both reasons are the correct explanation for the assertion

2. Both reasons are incorrect explanations for the assertion

3. Reason 1 is correct and Reason 2 is incorrect

4. Reason 2 is correct and Reason 1 is incorrect

Ans: Reason 2 is correct and Reason 1 is incorrect

10. State which of the following is true.

1. Anion comes from a base

2. Cation comes from an acid

3. Acid is a substance which donates a proton.

4. The base is a substance which donates a neutron.

Ans: Acid is a substance which donates a proton.

Conclusion

A dry test is one of the preliminary tests which is performed to identify the acidic and basic radicals present in salt. Preliminary tests do not indicate the exact radicals of salt, rather they are the probable ions which might be present in the salt.