Question

Arrange the compounds in each set in order of increasing basicity (a) Magnesium acetate, magnesium hydroxide, methylmagnesium bromide (b) Sodium benzoate, sodium \(p\) -nitrobenzoate, sodium acetylide (c) Lithium hydroxide, lithium ethoxide, lithium formate

Short answer

(a) Magnesium acetate < Magnesium hydroxide < Methylmagnesium bromide (b) Sodium p-nitrobenzoate < Sodium benzoate < Sodium acetylide (c) Lithium formate < Lithium hydroxide < Lithium ethoxide

Step-by-step solution

Understand Basicity

Basicity refers to the ability of a compound or ion to accept protons. The more readily a compound can accept a proton, the more basic it is. Typically, this involves looking at the stability of the anion formed after accepting a proton and the strength of the bond between the proton and other atoms in the compound.

Compare Basicity for Part (a)

For the compounds in part (a): - **Magnesium acetate**: This is a salt of a weak acid (acetic acid), thus relatively more basic than neutral acetic acid but weak overall. - **Magnesium hydroxide**: Basic due to the presence of a hydroxide ion (OH^-), which is a strong base. - **Methylmagnesium bromide**: This is a Grignard reagent, a strong base due to the presence of the highly reactive methyl group that can donate electrons readily. The order of increasing basicity is: Magnesium acetate < Magnesium hydroxide < Methylmagnesium bromide.

Compare Basicity for Part (b)

For the compounds in part (b): - **Sodium benzoate**: A salt of benzoic acid; moderately basic. - **Sodium p-nitrobenzoate**: Contains a nitro group which is electron-withdrawing, reducing basicity relative to sodium benzoate. - **Sodium acetylide**: A strong base due to the acetylide ion (C≡C^-), highly reactive. The order of increasing basicity is: Sodium p-nitrobenzoate < Sodium benzoate < Sodium acetylide.

Compare Basicity for Part (c)

For the compounds in part (c): - **Lithium hydroxide**: A strong base due to the presence of hydroxide ions. - **Lithium ethoxide**: An even stronger base than hydroxide because the ethoxide ion (C2H5O^-) is more reactive. - **Lithium formate**: A salt of a carboxylic acid (formic acid), making it less basic. The order of increasing basicity is: Lithium formate < Lithium hydroxide < Lithium ethoxide.

Key concepts

Magnesium Compounds

Magnesium compounds show varying levels of basicity depending on their structure. Basicity reflects how likely a compound is to accept a proton. Let's explore some common magnesium compounds:

• Magnesium Acetate: This compound is formed from a weak acid, acetic acid. Thus, it isn't very basic but is more so than neutral acetic acid. Being a salt of a weak acid, its basicity is quite low.
• Magnesium Hydroxide: Known as milk of magnesia, this compound contains hydroxide ions, which are strong bases. The hydroxide ions make it significantly more basic than magnesium acetate.
• Methylmagnesium Bromide: This is a Grignard reagent, famous for its strong basicity. The methyl group is highly reactive, enabling it to readily donate electrons and accept protons, making it the strongest base among the magnesium compounds listed here.

Sodium Salts

Sodium salts can vary widely in their basicity due to the nature of the anion they are paired with. Here's how some sodium salts compare:

• Sodium Benzoate: Derived from benzoic acid, sodium benzoate is moderately basic. The compound’s aromatic ring participates less in proton acceptance compared to others.
• Sodium \(p\)-Nitrobenzoate: This compound has a nitro group that withdraws electrons, which decreases its basicity relative to sodium benzoate. Electron-withdrawing groups limit the compound's ability to accept protons.
• Sodium Acetylide: This salt is highly basic due to the presence of the acetylide ion, \(\text{C}\equiv\text{C}^-\). The negative charge on the acetylide ion makes it extremely reactive and eager to accept protons, making it the strongest base among these sodium salts.

Lithium Compounds

Lithium compounds demonstrate a range of basicity, often influenced by their organic or inorganic nature. Here's a look at several lithium-based compounds:

• Lithium Hydroxide: Like other hydroxides, lithium hydroxide is a strong base, readily dissociating to release hydroxide ions in solution. This makes it quite a robust base.
• Lithium Ethoxide: This compound is an organic base, stronger than lithium hydroxide. The ethoxide ion, \(\text{C}_2\text{H}_5\text{O}^-\), enhances basicity through its ability to donate electrons effectively.
• Lithium Formate: Lithium formate, a salt of formic acid, is less basic. Like other salts of weak acids, its capacity to accept protons is limited, making it the weakest base among the lithium compounds discussed here.