Chem 205 Quiz 2

Which of the following species is not a Brønsted-Lowry base? 1. BF3 2. PO4^3- 3. H2O 4. NH3

BF3 is not a Brønsted-Lowry base because it cannot accept a proton due to the absence of an available pair of electrons. NH3, H2O, and PO43− can all act as bases by accepting protons

Which of the following compounds is the strongest acid?

BrCH2OH *Reason: BrCH2OH>CH3OH>CH3Cl>CH3NH2 CH3OH is weak acid . CH3NH2 is base BrCH2OH is strong acid. on alpha carbon electron with drawing groups are increases the acidic nature of acidic are increases.

What is the correct classification of the following compound? CH3-O-CH3

Brønsted-Lowry base and Lewis base

Which of the following compounds is not a Lewis acid? I. AlCl3 II. CBr4 III. HCl IV. H2O

CBr4 *reason: CBr4 (Carbon tetrabromide) is a non-polar covalent compound composed of carbon and bromine atoms. It does not have any vacant orbitals or electron-deficient atoms capable of accepting electron pairs. Thus CBr4 is not a Lewis acid.

Which of the following species is the conjugate base of methanol, CH3OH?

CH3O-

Which of the following will proceed as written? CH3OH+NaCl⟶NaOEt+HCl CH3OH+NH3⟶CH3O−+NH4+ CH3ONa+HCl⟶CH3OH+NaCl CH3OH+H2O⟶CH3O−+H3O+ .

CH3ONa+HCl⟶CH3OH+NaCl In the provided reactions, the some reactants are NaCl,NH3 , HCl and H2O . From these, it is clear that the HCl is stronger acid as compared to the other reactants. Stronger acid means capable to do the substitution as compared to others. It means, the reaction which takes place is: CH3ONa+HCl⟶CH3OH+NaCl . Explanation: More the stronger acid, more ability to do the substitution of the atoms in between the elements takes place.

Which of the following ranks the compounds in order of increasing basicity, putting the least basic first?

CH4 < CH3OH < CH3NH2 *Reason: The basicity is mainly depends on the acceptance of the proton. more ability to accept the proton more will be basicity. Basicity is inversely proportional to the electronegativity of the atom. - CH3OH and CH3NH2 both have non bonded electron but oxygen atom have more electronegative than Nitrogen atom So amine easily donate non electron but alcohol do not donate easily non bonded electron. So amine is more basic than alcohol - CH4 have no negative charge and have no non bonded electron so it is least basic

Which of the following ranks the compounds in order of increasing acidity, putting the least acidic first?

CH4>NH3>H2O *Reason: - CH4 (methane) - In methane, the hydrogen atom is bonded to carbon. Carbon is less electronegative than nitrogen and oxygen, so the H−C bond is relatively non-polar. Methane is the weakest acid among these compounds. - NH3 (ammonia) - In ammonia, the hydrogen atom is bonded to nitrogen. Nitrogen is more electronegative than carbon, leading to a more polar H−N bond compared to H−C in methane. Ammonia is a stronger acid compared to methane. -H2O (water) - In water, the hydrogen atom is bonded to oxygen. Oxygen is even more electronegative than nitrogen, resulting in a highly polar H−O bond. Water is the strongest acid among these compounds due to its highly polar bond.

Which is the conjugate base in the following reaction? HCl + H2O <=> Cl- + H3O+

Cl- *reason: The concept of conjugate acids and conjugate bases developed by the Bronsted - lowry acid-base theory. By losing a proton of compound, conjugate base is formed. Conjugate base is a base. it can abstract the proton and transformed into it's compound. Acid + Base ⇌ Conjugate Base + Conjugate Acid so, in equation HCl + H2O = Cl- + H3O+ here, Cl- can abstract proton from oxonium ion and transformed into its compound HCl. and oxonium ion is an behaves like acid, by donating a proton to Cl- . so oxonium ion is conjugate acid and conjugate base is Cl-. so, in conclusion the conjugate base is Cl-. First option is correct.

Which of the following compounds has the lowest pKa?

H2S: pKa= 7

Consider the following structures I-IV. Which two species represent a conjugate acid-base pair?

I and II

Identify the Lewis base in the following reaction.

I. Br2 *reason: Br2 donates electron pair to Febr2, so Br2 acts as a lewis base.

Which of the following would have the lowest pKa? I. CH3CH2CH2CH II.ClCH2CH2CH2CH2COOHClCOOH III. CH3CH2CHClCH2COOH IV. CH3CHClCH2CH2COOH

I. CH3CH2CH2CH *reason: The polar group is O−H bond and hydrogen can be easily removed . The carboxylate ion is stabilized by −Inductive effect of −Cl group. The Inductive effect depends on the distance of separation. Closer the −Cl group, more is the effect. In the last molecule, Cl group shows greater Inductive effect on the carboxylate ion and is more stable than the rest. Cl is an electron Withdrawing group(EWG) due to its high electronegativity. The EWG increases the acidity by stabilizing the anion formed after the removal of Hydrogen whereas Electron Donating Groups decrease the acidity of a compound.

Rank the following compounds in order of increasing acidity, putting the least acidic first. I. CH3OOH II. FCH2COOH III. ClCH2COOH IV. BrCH2COOH

I<IV<III<II *reason: F>Cl>Br>H (electronegativity)

What are the products of the following proton transfer reaction?

II. *reason: As in ketone oxygen contains 2 lone pairs in between this two one l.p. will be protonated by H+ coming from H2SO4. And H2SO4 becomes HSO4- as 1 proton is eliminated by ketone.

Rank the following conjugate bases in order of increasing basicity, putting the least basic first. I. NH2- II. HO- III. CH3-

II<I<III *reason: The conjugate acid pair of given bases is ammonia, water, and methane respectively (by adding a proton to each of them). As per the conjugate acid-base pair theory, if acid is strong it's conjugate base will be weak. Thus using this we can compare the basicity of these three ions We know, when a proton is bound to an electronegative atom, it becomes more acidic. Thus among these molecules, water is the most acidic molecule, then comes ammonia and then methane will come (electronegativity decreases in the order O>N>C) Thus on comparing the conjugate bases, CH3- is the strongest base, the NH2- will come and the least basic among this is OH-. (Reverse order of acidity of their conjugate acids)

Rank the following compounds in order of decreasing acidity, putting the most acidic first. I. CH3CH2OH II. CH3CH2NH2 III. ClCH2CH2OH

III>I>II *reason: Cl>O>N (electronegativity)

Rank the following compounds in order of decreasing acidity, putting the most acidic first. I. CH3OCH3 II. CH3CHO III. CH3CH2OH IV. CH3COOH

IV>III>II>I *Reason: Acidity is based on the stability of conjugate base it forms when it loses a proton. CH3OCH3 (Dimethl ether) - This compound does not have an acidic proton. It doesn't donate proton and is not acidic. CH3CHO (Acetaldehyde)−It has a proton in the carbonyl group and it loses a proton to produce CH3CO−, which is less acidic. CH3CH2OH (Ethanol)−It has a proton in the carboxyl group and it loses the proton to form CH3CH2O−, which is more acidic. CH3COOH (Acetic acid)−It is the most acidic among the given compounds.

What is the role of methylchloride (CH3Cl) in the following reaction?

Lewis base Methyl chloride(CH3Cl) serves as a Lewis base in the reactionCH3Cl+AlCl3. To create a coordinate bond with the aluminium atom in AlCl3, it transfers two electrons from its chlorine atom. This interaction emphasises CH3Cl′s ability to supply electrons and its function as a Lewis base in the reaction.

Which of the following statements about Lewis bases is true?

Lewis bases are electron pair donors.

Which of the following statements is a correct definition for a Brønsted-Lowry acid?

Proton donor

Which of the following compounds is the weakest acid?

SiH4 *Reason: SiH4 is weakest acid it's pka value is very high approximately 47 therefore this is weakest acid from the given compounds

Identify the acid/conjugate acid (in that order) in the following reaction: H2O + CH3COOH <=>H3O+ + CH3COO-

acid: CH3COOH conjugate acid: H3O+ *reason: # Acids are the substances which have tendency to give H+ ions. # Conjugate acid of a base is formed by adding one H+ ion in base.

Identify the base/conjugate base (in that order) in the following reaction: H2O + CH3COOH<=> H3O+ + CH3COO-

base: H2O conjugate base: CH3COO-

What is the direction of equilibrium when acetylene (C2H2) reacts with ethoxide (CH3CH2O-) in an acid-base reaction?

left *reason: To predict the direction of equilibrium reaction, we have to know the value of pK pK of Acetylene = 25 pK of Ethanol = 16 ∆pK = pK (product) - pK (reactant) ∆pK = (16 - 25) ∆pK = -9 When ∆pK = 0 means Perfect Equilibrium ∆pK = 0 to -10 means Reactant dominant ∆pK = 0 to +10 means Product dominant ∆pKa = -9 means Reactant dominant Hence, Equilibrium will shift in left direction. Therefore, Backward Reaction will favoured