Content Curator
Selenic acid is a colourless, crystalline, soluble strong dibasic acid having the chemical formula H2SeO4. The acid form and inorganic salts of dihydrogen selenium tetraoxide are included. It's a selenium oxoacid whose structure is more precisely characterised as (HO)2SeO2. It can be produced by oxidising lower oxidation states of selenium compounds. One way is to oxidise selenium dioxide using hydrogen peroxide.
| Table of Content |
Key terms: Selenic Acid, Ammonia, Hydrophilic, Oxidizer, Crystalline, Selenium oxoacid, Viscosity
Also Read: Selenium
Selenic Acid Structure
[Click Here for Sample Questions]
The molecule is tetrahedral, as predicted by VSEPR THEORY. The Se–O bond length is 161 PM. In the solid-state, it crystallises in an orthorhombic structure.
Selenic Acid Chemical Structure
Selenic Acid Properties
[Click Here for Sample Questions]
- Selenic acid shows up as white crystals. Exceptionally destructive to skin, eyes, and mucous films. Destructive to metal. Harmful by skin assimilation and by ingestion.
- It has a molar mass of 144.9734 grams per mol, a density of 2.95 g/cm cubic, a melting point of 58 degrees Celsius, and a boiling point of 260 degrees Celsius.
- It dissolves in sulfuric acid but not in ammonia.
Also Read: Potassium Sulphate
Preparation of Selenic Acid
[Click Here for Sample Questions]
Selenic Acid is made by oxidising lower-oxidation-state selenium compounds. The oxidation of selenium dioxide with hydrogen peroxide is one method:
SeO2 + H2O2 → H2SeO4
Unlike the hydration of sulphur trioxide to produce sulphuric acid, the hydration of selenium trioxide is impracticable. Selenic acid can also be made by oxidizing selenous acid (H2SeO3)with halogens like chlorine or bromine, or by using potassium permanganate. Using chlorine or bromine as an oxidizing agent, on the other hand, creates hydrochloric or hydrobromic acid as a by-product, which must be eliminated from the solution since they can reduce selenic acid to selenous acid.
Another way to make selenic acid is to use chlorine to oxidize elemental selenium in a water suspension:
Se + 4 H2O + 3 Cl2 → H2SeO4 + 6 HCl
Reactions of Selenic acid
[Click Here for Sample Questions]
- Selenic acid, like sulphuric acid, is a powerful acid that is hydrophilic in nature and water-soluble. Viscosity is a property of concentrated solutions. It is known that crystalline mono and di-hydrates exist. The monohydrate melts at 26 degrees Celsius, while the dihydrate melts at 51.7 degrees Celsius.
- A red-yellow solution of gold(III) selenate is formed when hot, concentrated selenic acid interacts with gold:
2 Au + 6 H2SeO4 → Au2(SeO4)3 + 3 H2SeO3 + 3 H2O
- Selenic acid reacts with barium ions to form BaSeO4, which is like sulphate. Selenate salts are like sulphate salts; however, they are more soluble. The crystal structure of several selenate salts is identical to that of the corresponding sulphate salts.
- Treatment with fluorosulphuric acid gives selenoyl fluoride:
H2SeO4 + 2 HO3SF → SeO2F2 + 2 H2SO4
Also Read: Sulphuric Acid
Uses of Selenic Acid
[Click Here for Sample Questions]
- As a specialist oxidizing agent, selenic acid is utilized.
- It was added to chromium-plating baths to help prevent plated vehicle items from pitting, blistering, and rusting, particularly in the North American snow belt.
- It's found in metal cleaners, drain cleaners, and toilet cleaners.
Also Read: Polymorphism
Things to Remember
- Selenic acid is an organic compound with the chemical formula H2SeO4. Selenic acid is a selenium oxoacid. It is the conjugate acid of a hydrogen selenate.
- Mitscherlich invented it in 1827 when he hung lead selenate in water and precipitated the lead using hydrogen sulphide. Selenic acid can also be made by oxidizing aqueous solutions of selenious acid with appropriate reagents, such as chlorine or bromine.
- Selenic acid is a crystalline white substance. Skin, eyes, and mucous membranes are all severely harmed. Metals are corroded by this substance. Toxic when ingested and absorbed via the skin.
- Selenic acid is a more powerful oxidizer than sulphuric acid, capable of releasing chlorine from chloride ions while also reducing to selenous acid:
H2SeO4 + 2 H+ + 2 Cl− → H2SeO3 + H2O + Cl2
Also Read: Aldehydes, Ketones, and Carboxylic Acids
Sample Questions
Ques. Selenious acid (H2SeO3), a diprotic acid has Ka1=3.0×10−3 and Ka2=5.0×10−8. What is the [OH−] of a 0.30 M solution of a selenious acid? (3 marks)
(A) 5.0 * 10-6
(B) 3.5 * 10-13
(C) 3.5 * 10-11
(D) 2.85 * 10-3
Ans. The correct option is (B).
Explanation: Here also, Ka2<<<Ka1 so second ionization can be neglected
∴ H2SeO3⇔HSeO3− +H+
or Since (10×0.03)−x≈(0.03×10) since x is very small
∴ Ka11=3×10-3 = (0.03×10) / x2
or x = √ 9×10−4 = 3×10−2
∴ [OH−] = [H+] / 10−14 = 3.3×10−13 ≈ 3.5×10−13
Ques: What is the pH of a 0.10 M solution of barium hydroxide, Ba (OH)2? (3 marks)
(A) 13.30
(B) 11.7
(C) 11.30
(D) None of the above
Ans: Correct option is (A)
pH =13.30
Barium hydroxide is a strong base for both stages of dissociation:
Ba (OH)2(s) → Ba2+ + 2OH–
So the solution will have 0.20 M hydroxide ions. Now use the auto dissociation product for water:
[H+][OH–] = 1.0×10-14M
[OH–] = 2.0 × 10-1M
[H+] = 5.0 × 10-14M
And then pH = −log10 ([H+] = 5.0 × 10-14)
= 13.30
Ques: Write the formula for selenic acid. What are the anion name and formula? (2 marks)
Ans: Selenic acid is prepared by oxidizing selenium dioxide using hydrogen peroxide. The chemical formula of selenic acid is H2SeO4.
The anion formed from selenic acid is a selenate ion. It is represented by the chemical formula SeO2−4. Selenate is a strong oxidizer. At room temperature, they are readily soluble in aqueous solutions.
Ques: Fluorine is more electronegative than Chlorine even then P-Fluorobenzoic acid is a weaker acid than p-Chlorobenzoic acid. State the possible reason for this. (2 marks)
Ans: The I and +M actions with the benzene ring are thought to be caused by fluorine and chlorine (owing to the presence of lone electron pairs). The I effect tends to enhance acidic strength, whereas the +M effect tends to reduce acidic strength.
Fluorine has a stronger I impact than chlorine because it is more electronegative. It does, however, have a stronger +M impact than chlorine (opposing factor). This might be because the carbon and fluorine atoms' 2p orbitals are comparable in size, but the carbon and chlorine atoms' orbitals aren't. As a result, p fluorobenzoic acid is less effective than p chlorobenzoic acid in terms of potency.
Ques: Arrange the following carbonyl compounds in increasing order of their reactivity in nucleophilic addition reactions (3 marks)
(a) Ethanal, propanal, propanone, butanone
(b) Benzaldehyde, p-tolualdehyde, p-nitrobenzaldehyde, acetophenone
Ans: (a) The carbonyl compounds are reactive towards nucleophilic addition processes in the following order: butanone, propanone, propanal, and ethanal.
Two elements influence reactivity. There are two types of steric and electronic factors.
(b) The following is the ascending order of reactivity:
acetophenone < p-tolualdehyde < benzaldehyde < p-nitrobenzaldehyde
Explanation: Acetophenone is the least reactive to nucleophilic addition since it is a ketone. The rest are aldehydes. Because the CH3 group present at the para position concerning the -CHO group will enhance the electron density on the carbonyl carbon atom due to the hyperconjugation effect, p-tolualdehyde is less reactive than benzaldehyde. As a result, as compared to benzaldehyde, the nucleophile attack is less severe.
Ques: Name the industries in which Carboxylic acids are used? (2 marks)
Ans: Organic acids are used in the food industry to make vinegar, sodium salts, and other soft beverages, while sodium benzoate is used to preserve goods. Acetic is used in the chemical industry to make dyes, fragrances, and rayons, among other things. Acetic acids are used to make rubber in the rubber manufacturing business. Many carboxylic acids are utilized in the pharmaceutical business to make various types of medications.
Ques: Which aldehydes are soluble in water? (3 marks)
Ans: The general rule of thumb is that aldehydes and ketones with fewer than six carbon atoms are water-soluble.
Explanation: A battle between the polar "head" and the nonpolar "tail" determines an aldehyde's or ketone's solubility. Because small aldehydes and ketones may establish hydrogen bonds with water, they are miscible with water in all concentrations.
However, as chain length increases, solubility diminishes because the hydrocarbon "tails" of the molecules must squeeze between water molecules. They must destroy the strong hydrogen connections that exist between water molecules without replacing them with something equally as excellent. As a result, the process becomes less energetically advantageous, and solubility declines.
The dividing line is between five and six carbon atoms if "soluble" is defined as "more than 1 g/100 mL." Pentanal and pentane-2-one are soluble, but hexanal and hexane-2-one are not.
Ques: Write the steps of the Etard reaction mechanism. (4 marks)
Ans: Etard response component:
- The response of Toluene with Chromyl Chloride prompts homolytic cleavage which is the breakdown so that each part gets equivalent pieces of electrons.
- Likewise, the C-H obligation of the methyl bunch is additionally separated.
- Toluene breaks to give hydrogen which bonds with the oxygens of two Chromyl Chloride atoms shaping two OCr(OH)Cl2.
- The two OCr(OH)Cl2 particles then, at that point, connect themselves to the carbon of the methyl gathering of Toluene. This is finished with the assistance of second oxygen which frames a temperamental complex compound additionally alluded to as brown complex.
Here our initial segment of the response is finished. This is trailed by :
- The hydrolysis of the shaky complex compound. This will bring about the trading of electrons of oxygen with the carbon of Toluene.
- The oxygen in the primary OCr(OH)Cl2 breaks the C-O bond and joins to the H+ of water shaping OCr(OH)2Cl2.
- The oxygen of the second OCr(OH)Cl2 will break the O-Cr bond-framing twofold bond with Carbon.
- The leftover Cr(OH)Cl2 bonds with OH of water again shaping OCr(OH)2Cl2.
- The two OCr(OH)2Cl2 then, at that point, get isolated to frame Benzaldehyde.
Here stage two is finished giving the completed item Benzaldehyde consequently finishing the Etard response.
Ques: Do ketones oxidized by Tollens' reagent just like aldehydes? (2 marks)
Ans: Ketones, unlike aldehydes, are not oxidized by Tollens' reagent. Tollens' reagent is a weak oxidizing agent, whereas ketones require a strong oxidizing agent to oxidize.
Hydrogen (H) atoms are not linked to the carbonyl group (c=o) in ketones.
The equivalent acid in aldehyde is formed when the hydrogen (H) atom is reduced. Ketones, on the other hand, fail to form a hydrogen atom connection with the carbonyl group, preventing them from passing the Tollens' Test.
Ques: State the chemical reactions of carbonyl compounds. (3 marks)
Ans: Because it attracts electron-rich compounds, the carbon atom in the carbonyl group is known to be electrophilic. Although some electrophiles can be represented as ions, oxygen atoms are dubbed nucleophiles because they have a low electron density. The following are some examples of carbonyl compound reactions:
Carbonyl Reduction- When carbonyl groups are reduced by hydride reagents like NaBH4 and LiAlH4 in the presence of baker's yeast, or by catalytic hydrogenation, this reaction happens.
Carbonyl Alkylation- This process uses organometallic chemicals including organolithium reagents, Grignard reagents, acetylides, and others to alkylate carbonyl compounds.
Carbonyl Alpha Substitution Reaction- In this type of substitution reaction, an electrophile is employed to replace the hydrogen atom.
Ques: Why Aldehydes are more reactive than ketones? Explain. (2 marks)
Ans: Because of the following two factors, aldehydes are more reactive than ketones:
- The amplitude of positive charge on the carbonyl carbon in aldehydes is greater than in ketones, due to the lesser +1 effect of one alkyl group in aldehydes compared to the bigger +1 effect of two alkyl groups. As a result, nucleophilic addition reactions in aldehydes are more common than in ketones.
- Aldehydes are easier to oxidise than ketones because they have an H-atom on the carbonyl group.
Related Links:
Comments