Category: Chemistry Notes PPT

An important class of organic compounds containing the carbonyl group comprises aldehydes and ketones. Aldehyde has the RCH(=O) structure, while R₂C(=O) has the structure of a ketone.

 

In this article, we will study the following concepts in detail.

1. Test for aldehydes and ketones, 

2. How aldehyde and ketone can be distinguished by various tests.

Aim

Identify the presence of functional group aldehydes or ketones in the given organic compound.

 

Materials Required

The test of aldehyde and ketone-

1. Schiff’s reagent

2. Silver nitrate solution

3. Fehling’s solutions A

4. Fehling’s solutions B

5. Dilute ammonium hydroxide solution

6. 2,4-Dinitrophenylhydrazine reagent

7. Chromic acid

8. Sulfuric acid

9. Sodium bisulfite

10. Test tubes

11. Test tube holder

12. Beaker

 

Theory 

Aldehydes and ketones are volatile compounds with low molecular weights. Aldehyde and ketone identification is based on two types of reactions, the double bond addition reaction, and the oxidation reaction. 

 

In aldehydes, a hydrogen atom and aliphatic or aromatic radicals are attached to the carbonyl group. Formaldehyde is an exceptional case where two hydrogen atoms are attached to the carbonyl that is present in formaldehyde. In ketones, two aliphatic or aromatic groups are affixed to the carbonyl group.

 

Tests to Detect the Presence of Aldehyde and Ketone

1. 2,4-dinitrophenylHydrazine Test

Aldehyde and ketone react with a 2,4-dinitrophenylhydrazine test to give a yellow to orange color precipitate. The aldehyde test reaction is given below-

2. Sodium Bisulfite Test

When aldehydes and ketone react with Sodium bisulfite, crystalline precipitate.

 

Aldehyde and Ketone can be Distinguished By

1. Schiff’s Test

In some dye formulation reactions, such as the reaction between sodium bisulfite and fuchsine, the Schiff reagent is the product produced. It is used to detect an aldehyde’s presence. A magenta-coloured dye with a chemical formula C20H20N3·HCl, which is decolourized by sodium bisulfate, is fuchsine or rosaniline hydrochloride. A pink colour indicates the presence of an aldehyde group.

2. Fehling’s Test

The Fehling test consists of a solution that in laboratories is normally freshly prepared. The solution occurs in two different forms known as Fehling’s A and Fehling’s B. Fehling’s A is a blue copper(II) sulfate solution. A clear liquid consisting of potassium sodium tartrate (Rochelle salt) and a powerful alkali, normally sodium hydroxide, is Fehling’s B. Solutions A and B are prepared separately.

 

The deep blue ingredient is the bis(tartrate) complex of Cu2+. Cu2+ is reduced to Cu+ when the aldehyde compound is treated with Fehling’s solution, and the aldehyde is reduced to acids. A red precipitate is formed during the reaction.

 

 

3. Tollen’s Test

The Tollens test is a chemical test used to distinguish sugar reducers from non-sugar reducers. This test is known as the silver mirror test. Aldehydes react by giving a grey-black precipitate or a silver mirror to the Tollens reagent. A freshly prepared reagent from Tollen should always be used. In the Tollens reagent, aldehydes are oxidized to the corresponding acid, and silver is reduced from the +1 oxidation state to its elemental form. Ketones usually do not respond to this test.

RCHO + 2[Ag(NH3)2]OH → R-COONH4+ 3NH3 + H2O + 2Ag↓(silver mirror)

4. Test with Chromic Acid

A green to blue precipitate is given by aldehydes reacting with chromic acid. With chromic acid, ketones do not react. Some of the primary and secondary alcohols are also tested.

R-CHO + 2CrO3 + 3H2SO4 → 3R-C(O)-OH + 3H2O + Cr2(SO4)3(green colour)

5. Sodium Nitroprusside Test:

Ketones only give this test and not aldehyde. An anion is formed when ketone reacts with an alkali, further this anion reacts with sodium nitroprusside to form a coloured complex. The red colour shows the presence of ketones. 

CH3 + OH^–→ CH3COCH^2–+ H2O

[Fe(CN)5NO]^2- + CH3COCH^2– → [Fe(CN)5NO.CH3COCH2]^3-

 

Procedure and Observation:

 

Results:

The given organic compound has an aldehyde/ ketone functional group present.

 

Precautions:

1. conduct the experiment, the reagents should be freshly prepared. 

2. Not directly on the flame to heat the reaction mixture. 

3. Wash the test tube with nitric acid to destroy the silver mirror after running the Tollen test, since it is explosive material.

 

Did you know?

Formaldehyde has an odor that is unpleasant. It is difficult to handle in a gaseous state due to its reactivity. Therefore, it is dissolved in water for many applications and marketed as a 37 percent to 40 percent aqueous solution called formalin. Proteins are denatured by formaldehyde, making them insoluble in water and resistant to bacterial decay. For this reason, in embalming solutions and in preserving biological specimens, formalin is used.

 

DNPH Test

The use of the reagent 2, 4-dinitrophenylhydrazine allows imines to be formed from ketones or aldehydes (DNPH). The carbonyl of an aldehyde or ketone is attacked by the main amino group of the DNPH in an environment with an acidic nature in this addition-elimination reaction. A hydrazone is formed as a result of the condensation reaction, and it precipitates out of the solution.

 

Non-conjugated ketones or aldehydes are indicated by yellow precipitates, whereas conjugated systems are indicated by red-orange precipitates. This test is used to distinguish ketones and aldehydes from alcohols and esters, which do not react with DNPH and therefore do not generate a precipitate. The ketone or aldehyde derivatives are crystalline solids with well-defined melting temperatures that have been documented in the literature and can be used to identify specific compounds.

 

Haloform Test

The haloform test is another method for determining whether a ketone is methyl ketone. A methyl group is attached to the carbonyl carbon in methyl ketones (RCOCH3). Hydrogen (methyl aldehyde), an alkyl group, or an aryl group can be used as the R group.

Under basic conditions, the haloform test response mechanism occurs. The ketone first passes through a keto-enol tautomerization process. The nucleophilic enolate then attacks the iodine, resulting in the formation of an iodine ion and a halogenated ketone. This process is repeated three times more until all hydrogens in the ketone methyl group have been replaced by iodine. The hydroxide then combines with the electrophilic carbon core of the carbonyl to generate a tetrahedral intermediate with a negatively charged oxygen that is single bonded to the carbonyl. The trihalomethane group departs as a stable leaving group when the C-O double bond is formatted. Finally, the negatively charged trihalomethane group deprotonates the produced carboxylic acid, yielding the haloform — trihalomethane — and a carboxylate. If the halogen is iodine, the precipitate will be a distinctive yellow tint. Only methyl ketones will undergo this reaction, and any other carbonyl-containing molecule will have a negative result.

Exothermic welding which is also known as thermite welding is a process that uses heat from an exothermic reaction to produce coalescence between two metals.  The name is derived from ‘thermite’ which is given to reactions happening between metal oxides and reducing agents. The thermite heat consists of metal oxides having a low heat of formation and metallic reducing agents which, when oxidised, have high heat of formation. The excess heat generated from the reaction products provides the energy source to form the weld between two metals.

 

The powder consists of aluminium and the oxide of other metals like iron. Once heated, it gives off an enormous amount of heat which is a result of the chemical combination of aluminium with the oxygen of the oxide. The reaction temperature can rise about 2400° C.

 

For joining the steel parts, thermite welding is mainly used. Thus the common components of thermite welding are the iron oxide that is present in about 78% and the aluminium powder that is present in about 22%. The proportion of 78% and 22% respectively is determined by the combustion reaction of the aluminium and the reaction is as follows:-

 

8Al + Fe₃O₄→ 9Fe + 4Al₂O₃

 

The product of the combustion reaction which is iron and aluminium oxide is heated up to 2500°C which is equal to  4500°F. Therefore the sand or the ceramic mould is filled up with liquid iron. The slag which is an aluminium oxide that then floats up to the surface is then removed from the weld surface.

 

To repair steel castings and forgings, for joining railroad rails, steel wires and steel pipes, for joining the large cast and forged parts, thermite welding is used. 

Advantages and Disadvantages of Thermite Welding

Advantages of thermite welding are as follows:

1. It is a very simple procedure or process to join two similar or dissimilar metals together quickly. 

2. As no costly power supply is required, this process is very economical and convenient. 

3. The thermite process is used in a place where there is no availability of electricity.
   

Disadvantages of thermite welding are as follows:

1. Thermite welding is essentially used for parts of every section of ferrous metals.

2. It is proven to be economical for the welding of light parts and cheap metals.

3. It has a very slow welding rate.

4. The presence of a very high temperature may cause distortion and a change in grain structure in the welded region.

5. The welded region also contains slag contamination and hydrogen gas.
   

What is Thermite Mixture? 

It is a mixture of fine aluminium powder and iron oxide in a ratio of about 1:3 by weight.

 

Thermite formula is given by Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat

 

In this topic we have discussed what thermite is, Let’s understand the process of Thermite Welding.

Process of Thermite Welding

It is the most effective, highly mobile method used for joining heavy section steel structures like rails. The high heat input and metallurgical properties of the thermit steel make the process ideal to weld high strength, high hardness steels which are used in modern rails.

 

Thermit Welding always requires skilled labour for the welding process and must not be undertaken by someone who has not been trained to use it. Thermite welding results in a thermite reaction that involves the burning of thermite which is a mixture of iron oxide and fine aluminium powder present in the ratio of 1:3 by weight.

 

As a result of the reaction that is preheating of the thermite mixture up to 1300° centigrade the temperature reaches up to 3000° centigrade but it is essential in order to start the reaction. The reaction is as follows along with the diagrammatic representation of the thermite welding process. 

8 Al + 3Fe₃O₄  [longrightarrow] 9Fe + 4Al₂0₃ + Heat(3000˚C, 35 kJ/kg of mixture)

 

()

 

There is a greater affinity for aluminium to react with oxygen. Therefore the aluminium reacts with ferric oxide in order to generate pure iron and slag Aluminium oxide. Aluminium oxide then floats on the top of the metal pool in the form of slag and the pure iron that is formed settles below. It is because there is a large density difference between the two.

Steps to be Followed while Doing Welding

1. A proper gap must be prepared between the two rails, which must be accurately aligned by means of straight edges to ensure the finished joint is perfectly straight and flat.

2. After the first step, the second step involves pre-formed refractory moulds that are manufactured to accurately fit it around the specific rail profile, are clamped around the rail gap and then sealed in position. Equipment used in locating the preheating burner and the thermit container is then assembled afterwards.

3. The weld cavity which is formed inside the mould is preheated using an oxy-fuel gas burner with accurately set gas pressures for a given time. The quality of the finished weld highly depends on the precision of this preheating process.

4. On completion of the preheating process, the container is fitted at the top of the moulds, the portion is ignited and the subsequent exothermic reaction produces the molten Thermit Steel. The container consists of an automatic tapping system enabling the liquid steel – which is at a temperature in excess of 2,500°C – to discharge directly into the weld cavity.

5. The welded joint is allowed to cool down for a certain amount of time before the excess steel and the mould material are removed from the top of the rail with the help of a hydraulic trimming device.

6. Once cold the joint is cleaned of all debris, the rail running surfaces are inspected. The finished weld must be inspected carefully before it is passed as ready for service.
   

Types of Welding

There are two types of welding:

Fusion Welding: It will heat and fuse the metal parts, the thermite mixture will act as a filler metal also.

 

Pressure Welding: It will heat the metal part and raise them for forging temperature and forging force is applied in order to join them.

Conclusion

In this article, we have learnt about thermite welding, its advantages and disadvantages along with the process of thermite welding. We also learnt about what steps to be followed while doing welding, and what are the other types of welding. 

You may be familiar with a lot of chemicals and you may even be using many of those. One such chemical is Tin Oxide. It has two types viz; Tin Monoxide and Tin Dioxide. In this article, we are going to cover the properties, uses and preparation of both these types. 

Tin oxide is an inorganic compound composed of tin and oxygen. Tin belongs to the fourteenth group of the modern periodic table. Another name of tin is stannum. Tin generally forms two types of oxides, one is stannous oxide and another one is stannic oxide. In this article, we will discuss the types of tin oxides, SnO2 compound name, SnO2 chemical name, tin oxide formula, and SnO2 name.

Types of Tin Oxide

Tin forms two types of oxides:

1. Tin monoxide

2. Tin Dioxide

 

1. Tin Monoxide – 

Tin monoxide is also known as stannous oxide. Tin monoxide is an inorganic compound composed of one tin and one oxygen element. The tin oxide formula is SnO. The oxidation state of the tin in this compound is +2. Therefore it is represented as tin (II) oxide. This compound exists in two forms; a stable form bluish-black in color while another one is the metastable form also known as red form.

 

Properties of Tin (II) Oxide

Physical Properties of Tin Oxide

• Tin (II) oxide exists in the solid- crystalline form.

• It appears bluish-black in color.

• The melting point of tin (II) oxide is 1976℉.

• The density of this is 6.45 g/cm3.

• Tin (II) oxide is not soluble in water.

 

Tin (II) Oxide Structure

The tetragonal PbO layer structure of black -SnO contains four coordinate square pyramidal tin atoms. The rare mineral romarchite is found in nature in this form. The asymmetry is commonly attributed to a sterically active lone pair, but electron density calculations reveal that it is caused by an antibonding interaction between the Sn(5s) and O(2p) orbitals. The lone pair’s electrical structure and chemistry define the majority of the material’s properties.

In SnO, non-stoichiometry has been observed.

Between 2.5 and 3 eV has been measured as the electronic bandgap.

le size.

 

Preparation of  Tin (II) Oxide

Heating the tin(II) oxide hydrate, SnO x H2O (x1),  which  forms  when  a  tin(II)  salt  reacts  with an alkali hydroxide such as NaOH, produces blue-black SnO.

The precipitate formed by the action of aqueous ammonia on a tin(II) salt can be gently heated to generate metastable, crimson SnO.

In the laboratory, SnO can be made as a pure material by heating tin(II) oxalate (stannous oxalate) in the absence of air or under a CO₂ environment. 

This process can also be used to make ferrous oxide and manganese oxide.

SnC2O4·2H2O → SnO + CO2 + CO + 2 H2O

SnO2 is formed when tin(II) oxide burns in the air with a dull green flame.

2 SnO + O2 → 2 SnO2 

When heated in an inert environment, disproportionation occurs, resulting in the 

formation of Sn metal and Sn3O4, which then reacts to form SnO2 and Sn metal.

4SnO → Sn3O4 + Sn;  Sn3O4 → 2SnO2 + Sn

SnO is amphoteric, forming tin(II) salts in strong acids and stannites containing Sn(OH)3 in strong bases. It forms the ionic complexes Sn(OH2)32+ and Sn(OH)(OH2)2+ when dissolved in strong acid solutions, and Sn3(OH)42+ when dissolved in less acid solutions. Anhydrous stannites, such as K2Sn2O3 and K2SnO2, are also known. To reduce the copper (I) to metallic clusters in the preparation of copper ruby glass, SnO is used as a reducing agent. 

2. Tin Dioxide- 

SnO2‘s name stands for Tin dioxide. Tin dioxide is also known as stannic oxide. Tin dioxide is an inorganic compound composed of one tin and two oxygen elements. SnO2 chemical name is a stannic oxide or tin (IV) oxide. The tin oxide formula for this oxide is SnO2. The oxidation state of the tin in this compound is +4. Therefore it is represented as tin (IV) oxide. Tin (IV) oxide also occurs in the mineral form in the earth’s crust. The mineral form of tin (IV) oxide is cassiterite. This mineral is one of the important and main ores of tin. SnO2 compound name represents the compounds of tin (IV) oxide which exist in ionic or covalent form.

 

Properties of Tin (IV) Oxide

Physical Properties of Tin (IV) Oxide

• Tin (IV) oxide exists in solid form.

• The color of tin (IV) oxide is colorless.

• The melting point of tin (IV) oxide is 2966℉.

• The density of this is 6.95 g/cm3.

• Tin (IV) oxide is not soluble in water.

 

Tin (IV) Oxide Structure

The rutile structure crystallizes using tin(IV) oxide. As a result, the tin atoms have six coordina
tes while the oxygen atoms have three. SnO2 is commonly thought of as an n-type semiconductor that lacks oxygen.

Stannic acid is the name given to the hydrous forms of SnO2. These materials appear to be hydrated SnO2 particles with a composition that reflects particle size.

Chemical Properties of Tin (IV) Oxide

• Tin (IV) oxide is thermally more stable than the SnO.

• Tin (IV) oxide is amphoteric in nature. It reacts with acid as well as with base.

• It reacts with strong acids and forms tin (IV) salts as a product.

• Tin (IV) oxide acts as a reducing agent as in this compound tin is in its highest oxidation state.

 

Preparation of Tin (IV) Oxide

2SnO + O2 → 2SnO2

4SnO → Sn3O4 + Sn

Sn3O4 → SnO2 + Sn.

 

Uses of Tin Oxides

• Tin oxides are used in making ceramic glasses.

• Tin oxide is used in the formation of different dyes.

• Tin oxides are used in polishing the surfaces.

• It is used as a sensor for gas sensing.

• Tin oxides are used as a precursor for various chemical reactions.

• It is used as an illuminating agent.

 

Tin oxide nanoparticles have magnetic characteristics that are exploited in magnetic data storage and magnetic resonance imaging; Energy-saving coatings and anti-static coatings are used as catalysts; In solar cells, as electrodes and anti-reflection coatings; Gas sensors, optoelectronic devices, and resistors are all used in the production of gas sensors; 

 

Did You know?

Why Should You Consider ? 

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Transition elements are elements found on the periodic table in Groups 3-12 (old groups IIA-IIB) The term refers to the fact that the d sublevel that is being filled is at a lower principal energy level than the s sublevel that came before it. Scandium, the first transition element, has an electron configuration of [Ar]3d14s2. Remember that the configuration is the opposite of the fill order, with the 4 s filling before the 3 d begins. The transition elements are frequently referred to as transition metals because they are all metals. They exhibit typical metallic properties as a group and are less reactive than the metals in Groups 1 and 2. 

Some of the more well-known ones are so unreactive that they can be found in nature in their free, or uncombined, form. Platinum, gold, and silver are examples. The transition elements are often referred to as “d -block” elements due to their unique filling order. Compounds containing a variety of transition elements are distinguished by their ability to be widely and vividly coloured. The d-orbitals absorb light of various energies as visible light passes through a transition metal compound dissolved in water. Visible light of a given energy level that is not absorbed results in a clear coloured solution.

Properties of Transition Elements

The transition elements’ general properties are as follows:

• They are typically metals with a high melting point.

• They have a variety of oxidation states.

• They usually combine to form coloured compounds.

• They are frequently paramagnetic.

• They have a high charge/radius ratio.

• High density and hardness.

• The boiling and melting points are both very high.

• Construct paramagnetic compounds.

• Variable oxidation states are displayed.

• Coloured compounds and ions are common.

• Create catalytically active compounds.

• Create stable complexes

Oxidation States

The number of electrons that an atom loses, gains, or appears to use when joining with another atom in a compound is related to its oxidation state. It also determines an atom’s ability to oxidise (lose electrons) or reduce (gain electrons) other atoms or species. Almost all transition metals have multiple oxidation states that have been experimentally observed. Ions are formed by adding or subtracting negative charges from an atom. Keeping the atomic orbitals in mind when assigning oxidation numbers aids in understanding that transition metals are a special case, but not an exception to this convenient method. 

An atom with an oxidation number of -1 accepts an electron to achieve a more stable configuration. The electron donation is then +1. When a transition metal loses electrons, it usually loses s orbital electrons first, followed by d orbital electrons. See Formation of coordination complexes for a more detailed discussion of how these compounds form. Most transition metals have multiple oxidation states because transition metals lose electron(s) more easily than alkali metals and alkaline earth metals. The valence s-orbital of alkali metals contains one electron, and their ions almost always have oxidation states of +1. (from losing a single electron). Similarly, alkaline earth metals have two electrons in their valence s-orbitals, resulting in +2 oxidation state ions (from losing both). Transition metals, on the other hand, are more complex and exhibit a variety of observable oxidation states, owing primarily to the removal of d-orbital electrons.

Tryptophan (Trp or W symbol) is an alpha-amino acid that is used in protein biosynthesis. Tryptophan has an alpha-amino group, an alpha-carboxylic acid group, and an indole side chain, making it a non-polar aromatic amino acid. In humans, it is essential, meaning that it can not be synthesized by the body and must be obtained from the diet. Tryptophan is the precursor of the neurotransmitter serotonin, the hormone melatonin, and vitamin B3 are all precursors of tryptophan. The codon UGG encodes it.

Frederick Hopkins first reported the isolation of tryptophan in 1901. Hopkins recovered tryptophan from hydrolyzed casein, recovering 4-8 g of tryptophan from 600 g of crude casein.

In this article, we will study tryptophan amino acids, source of tryptophan, and tryptophan and serotonin In detail.

Lysine and Tryptophan

A few similarities are shared between lysine and tryptophan. They are both amino acids used to make proteins — and they are important, meaning you have to get them from your diet because they can’t be created by your body. You have a greater chance of not getting enough lysine and tryptophan than other amino acids,  which makes them both amino acid-limiting. Otherwise, they each have functions that are unique.

Physical Properties of Tryptophan

It is a solid colour, slightly yellowish-white, with no odour and a flat taste. C₁₁H₁₂N₂O₂ is its chemical formula and has a molar mass of 204.229 g·mol−1. It is soluble in hot alcohol, alkali hydroxides, ethanol, acetic acid, but insoluble in chloroform and ethyl ether. Trp’s melting point is 290.5 dec °C and has a pKa value equal to 25 °C at 7.38. 

Source of Tryptophan

In most protein-based foods or dietary proteins, tryptophan is present. Chocolate, oats, dried dates, milk, yoghurt, cottage cheese, red meat, eggs, pork, poultry, sesame, chickpeas, almonds, sunflower seeds, pumpkin, buckwheat, spirulina, and peanuts are particularly abundant. 

Production of Tryptophan

As an essential amino acid, tryptophan in humans and other animals is not synthesized from simpler compounds, so it needs to be present in the diet in the form of proteins containing tryptophan. Tryptophan is usually synthesized by plants and microorganisms from shikimic acid or anthranilate. 

1. Anthranilate condenses with phosphoribosylpyrophosphate (PRPP), which as a by-product generates pyrophosphate. 

2. The ring of the ribose moiety is opened and subjected to reductive decarboxylation, producing indole-3-glycerol phosphate; this, in turn, is transformed into indole. 

3. The formation of tryptophan from indol and amino acid serine is catalyzed by tryptophan synthase in the last step.

Uses of Tryptophan

1. In the “anchoring” of the membrane, proteins inside the cell membrane, tryptophan and tyrosine residues play unique roles.

2. Tryptophan is also essential in glycan-protein interactions, along with other aromatic amino acids.

3. For the following substances, tryptophan acts as a biochemical precursor: 

• Serotonin (a neurotransmitter), synthesized by tryptophan hydroxylase.

• Melatonin (a neurohormone) is in turn synthesized from serotonin, via N-acetyltransferase and 5-hydroxy indole-O-methyltransferase enzymes.

• Niacin, also known as vitamin B3, is synthesized from tryptophan via kynurenine and quinolinic acids.

• Auxins (a class of phytohormones) is synthesized from tryptophan.

Tryptophan Depression (acts as an antidepressant)

Low levels of tryptophan are responsible for depression and anxiety. 

Since tryptophan is converted into 5-hydroxytryptophan (5-HTP), which is then converted into serotonin as a neurotransmitter, it has been suggested that tryptophan or 5-HTP intake can improve symptoms of depression by increasing the level of serotonin in the brain. In the United States and the United Kingdom as a dietary supplement for use as an antidepressant, anxiolytic, and sleep aid, tryptophan is marketed over the counter. It is also sold for the treatment of severe depression in several European countries as a prescription medication.

Did You Know?

High cellular levels of this amino acid activate a repressor protein that binds to the trp operon in bacteria that synthesize tryptophan. Binding this repressor to the tryptophan operon inhibits downstream DNA transcription that codes for the enzymes involved in tryptophan biosynthesis. So high tryptophan levels inhibit tryptophan synthesis via a negative feedback loop, and transcription from the trp operon resumes when the cell’s tryptophan levels go down again. This allows for tightly regulated and rapid responses to changes in the inner and outer tryptophan levels of the cell.

Titration is a method commonly used in laboratories for the quantitative estimation of an analyte i.e., using the method of titration the concentration or strength of a given chemical is determined.

 

Titration is basically used in volumetric analysis. Volumetric analysis can be used for many types of estimation and various types of titrations can be classified under the following categories:

1. Acid-base titration

2. Redox titration

3. Precipitation titration

4. Complexometric titration

Titration chemistry: In general, we can state that titration is a mode of quantitative analysis involving the estimation of the quantity of a chemical species by measuring the volume of the solution of that particular species in a suitable solvent. This method is based on the Law of Equivalence. So, it can be said that titration is the process of determining the volume of the reagents by bringing about a definite reaction to just completion.

 

The solution used during titration whose accurate concentration is known is called titrant and the substance whose volume is to be determined is said to be titrated.

 

Acid-Base Titration

The determination of the strength of a solution of acid by titrating it with a standard solution of a base, or the determination of the strength of a solution of alkali by the means of titration with a standard solution of acid, is termed as acid-base titration.

 

Titration chemistry in detail

The completion of the reaction between an acid and an alkali is termed neutralization and it proceeds with the formation of salt and water according to the general equation:

 

Acid + Base 🡪 Salt + Water

 

The detection of the endpoint of the titration is assisted by the addition of an indicator to the system under investigation. The indicator employed in these titrations is required to indicate the equivalent point rather than the true neutral point. At the point of equivalence, the pH of the solution could be equal to, greater than or less than 7, depending on the relative strengths of the acid and alkali. The salt formed by the solution at the end of the reaction may suffer hydrolysis to some extent and the pH of the solution will either be less than or more than 7. The solution is, thus, not truly neutral.

 

Indicators are used during acid-base titration. The indicators employed are either weak organic acids or weak organic bases. Their degree of dissociation is greatly affected by any alteration in the hydrogen ion concentration of the solution. An acid indicator can be expressed by the general formula HIn and the basic indicators as InOH. 

 

The dissociated and undissociated forms a dynamic equilibrium mixture of two tautomeric forms having different structural formulae and colours. One of these exists in an acidic medium, while the other in an alkaline medium. The change in pH causes the transformation from one form to the other and vice-versa; and consequently, a change in colour is seen.

 

Two such indicators are: Phenolphthalein, Methyl orange

 

pH range of some common acid-base indicators

 

Usually, an indicator such as phenolphthalein is used for the titrations involving a strong alkali and an indicator like methyl orange is used for titrations involving a strong acid.

 

What is Acid-Base Titration?

In order to do the titration, 100ml of the acid/base, that is to be titrated, is taken in a conical flask and a drop of phenolphthalein is added. Suppose, we take the acid in the flask. The counter chemical i.e. the base is taken in the burette and the titration is done until a sharp change in the colour is observed. Phenolphthalein gives pink colour in basic medium. When the sharp change in colour is seen, the addition of the base is stopped and the amount of base added is noted down. By using the concept of normality, and the law of equivalence, and using the known value of the concentration of the base, the unknown concentration of the analyte i.e., the acid that was titrated is determined. 

 

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The basic concept of acid base titration is based on this neutralization curve. The calculations for the determination of the strength or concentration of the unknown analyte are done using the law of equivalence.

 

Law of equivalence:

For a neutralization reaction, the number of equivalents of an acid must be equal to the number of equivalents of the base at the end point / equivalence point.

 

Normality X Volume = Number of equivalents

 

Normality = No. of equivalents of the solute dissolved in 1L of the solution.

 

No. of equivalents for an acid can be calculated as (Molecular weight) / Basicity. 

 

No. of equivalents for an acid can be determined as (Molecular weight) / Acidity.  

 

The overall titration chemistry lays its foundation on this law of equivalence only.

 

In general, during titration, an indicator showing change in color is taken. However, in potentiometric titrations, change in pH is taken for the acid base titration and in such titrations, there’s no requirement for the addition of an indicator because the end point is analyzed by the change in the pH of the solution.

 

Conclusion

This was all about acid base titration where an acid and a base were involved, of which the concentration of one was known and the concentration of the other was unknown; the titrations are performed in order to determine the concentration of the unknown using the known solution.