Which is a stronger base? a. H2 O or HO^- b. H2 O or NH3 c. CH3 CO^-or CH3 O^- d. CH3 O^-or CH3

Which is a stronger base? a. H2 O or HO^- b. H2 O or NH3 c....

Key Concepts

Resonance Stabilization Effects

Resonance stabilization involves the delocalization of charge over multiple atoms, which can stabilize a negative charge in a base. When a base is resonance-stabilized, its reactivity toward protons is reduced because the charge is spread out and less concentrated. This concept is particularly important when comparing bases like the acetate ion with the methoxide ion.

Brønsted–Lowry Acid–Base Theory

This fundamental concept defines bases as proton acceptors. In comparing base strengths, it is essential to consider how readily a species donates its electron pair to bond with a proton, which directly reflects its basicity. The theory frames the study of acid–base reactions by linking the properties of the base to the stability of its conjugate acid.

Conjugate Acid–Base Relationships and pKa

The strength of a base is commonly evaluated through the pKa of its conjugate acid. A higher pKa indicates a weaker conjugate acid and, by extension, a stronger base. This relationship is crucial for comparing species such as water versus hydroxide, or methoxide versus acetic acid anion, as their proton-donating abilities are interconnected with their basic strength.

Electronegativity and Atomic Size

Electronegativity influences an atom's ability to attract electrons, often making a more electronegative atom less willing to share its lone pair, thus affecting basicity. Additionally, atomic size can play a significant role; larger atoms with more diffuse electron clouds (such as sulfur compared to oxygen) may exhibit different basic strengths due to variations in polarizability and solvation effects. These factors are key when distinguishing between bases containing oxygen and sulfur.

Transcript

00:01 In this question we have been given five four different pairs of bases and in each case we need to find out the stronger base so first of all we have the pair which is h2o and h0 minus now the base is a species first of all we need to understand what is a base or but we can say what is the basic nature or we can say basicity so basicity is a characteristic of any species to donate its loan pair of elect to donate electron pairs to abstract protons now to abstract protons so proton is given as h positive or the hydrogen ketine so this is called a base now a base would be a stronger base if its conjugate acid is more stable which means let us take the example of this first subpart if h2o abstracts one proton we can say the species that we get would be h3o positive this is the conjugate acid of h2o base now if ho minus abstracts the same base or same proton we can say what we get would be h2o now h2o is the conjugate acid of ho minus now the thing is that the conjugate acid h2o is neutral it is neutral while h3o positive is charged and since it is charged it is going to be less stable because charge density is inversely proportional to this stability if the charge on the particular species is higher we can say it would be less stable while if the charge is uh less we can say stability would be very high that is how we can say that since the conjugate acid of h3u uh since the conjugate acid h3 o plus is more stable water would be a better since the conjugate acid h3o positive is less stable oh h minus would be a better base because its conjugate acid is more stable so this is how we can find out that h o minus is a better base than h2 o now moving on to the next subpart of this question that is h2 o and n h3 so here we can say that in h2 o the donor atom is oxygen while in n h3 the donor atom is nitrogen now the electronegativity of nitrogen is lesser than the electronegativity of oxygen which means that the electron pair on nitrogen would be easily donated easily donated then the loan pair of this h2 that is why we can say that n h3 would be a better base than h2 o here now moving on to the next sub part of this question which says that the two bases that we have would be ch3 c double bond o -o -o negative and the second base would be ch3 o negative now let us say that both of them abstract the proton here and then they would be forming ch3 c double bond o oh in the first case and ch3 oh in the second case so here we can say that ch3 c oh or the acetic acid is going to have a pcaa value of 4 .5 while the pca value for ch3 oh is given as 15 .5 which means that since the value of pca for ch3 oh is more it is going to be a weaker acid it is going to be a weaker acid which means that since its reactivity as an acid is low it is going to be a more stable it is going to be a more stable acid than acetic acid which is more reactive one that is how we can say that since the conjugate acid of cs3 -o -minus is more stable ch3 -o -minus would be a stronger acid than ch3 c double bond o and o minus now moving on to the next or last subpart of this question and this last subpart has two pairs has two bases in a pair that is ch3o minus and ch3 s minus so here we can say that if ch3 o minus abstracts one proton it is going to to give us ch3 oh similarly ch3 s minus on extracting one proton it gives us ch3 s h so here we can say that the more the stronger acid is ch3 s h this is the stronger acid which means that it is going to react more predominantly that is it is going to be less stable acid and this is how we conclude that ch3 oh h is more stable and this is the conjugate acid of the base ch3o negative.

04:29 So since the conjugate acid of ch3o negative is more stable, it is going to be a better, it is going to be a better base...

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