Problem 110 - Chemistry The Central Science In Si Units

Question

Arrange the following \(0.10 \mathrm{M}\) solutions in order of increasing acidity: (i) \(\mathrm{HCOONH}_{4},\) (ii) \(\mathrm{NH}_{4} \mathrm{Br}\), (iii) \(\mathrm{NaNO}_{3}\), (iv) \(\mathrm{HCOOK},(\mathrm{v}) \mathrm{KF}\).

Step-by-Step Solution

Answer

Increasing order of acidity: KF, HCOOK, NaNO_3, HCOONH_4, NH_4Br.

Step 1: Assess Compound Types

Classify each compound as an acidic, neutral, or basic salt based on its components. Strong acids or bases create neutral salts, while weak acids or bases can make acidic or basic salts. From the list: - (i) HCOONH_4 is a salt of the weak acid HCOOH and the weak base NH_3. - (ii) NH_4Br is a salt of the weak base NH_3 and the strong acid HBr, making it an acidic salt. - (iii) NaNO_3 is a salt of the strong base NaOH and the strong acid HNO_3, resulting in a neutral salt. - (iv) HCOOK is a salt of the strong base KOH and the weak acid HCOOH, making it a basic salt. - (v) KF is a salt of the strong base KOH and the weak acid HF, making it a basic salt.

Step 2: Determine Relative Acidic or Basic Strength

For each compound, identify which will dominate, the acidic ion or the basic ion. Generally, for salts of weak acids and bases, the weaker acid/base dictates the solution's nature. Here: - NH_4Br will be acidic because NH_4^+ is a conjugate acid of the weak base NH_3. - HCOONH_4's acidity is not clear directly but can be polarized slightly towards acidic due to NH_4^+. - NaNO_3 remains neutral due to its strong acid and strong base origin. - HCOOK and KF will be basic as they're derived from weak acids (HCOOH, HF) and strong bases (KOH).

Step 3: Rank Based on Acidity

Finally, arrange the solutions in order of increasing acidity by comparing their acidic nature: 1. KF (most basic) 2. HCOOK 3. NaNO_3 (neutral) 4. HCOONH_4 5. NH_4Br (most acidic)

Key Concepts

Acidic and Basic Salts

In Acid-Base Chemistry, salts can be classified as acidic, basic, or neutral based on their parent acids and bases. An acidic salt forms when a weak base reacts with a strong acid. In contrast, a basic salt comes from a strong base reacting with a weak acid. Neutral salts are the product when both the acid and the base are strong.

For instance, consider the salt NH_4Br. It arises from NH_3, a weak base, and HBr, a strong acid, which makes it an acidic salt. On the other hand, KF is a product of KOH, a strong base, and HF, a weak acid, classifying it as a basic salt. Finally, NaNO_3 is formed from NaOH and HNO_3, both strong, thus leading to a neutral salt. Understanding these classifications simplifies predicting the nature of a solution formed by these salts when dissolved in water.

• Acidic Salt: Weak base + Strong acid
• Basic Salt: Strong base + Weak acid
• Neutral Salt: Strong base + Strong acid

Acidity Ranking

Acidity ranking involves arranging solutions from least to most acidic based on their components. To understand acidity, consider the strength of the conjugate acids and bases.

A substance like NH_4Br is more acidic because NH_4^+ is the conjugate acid of the weak base NH_3, making it more influential in acidity determination. On the contrary, KF and HCOOK are basic salts due to their origins from strong bases and weak acids. Hence, they tilt the balance toward a basic or less acidic solution.

NaNO_3, being neutral, acts neither acidic nor basic, holding a middle ground. These nuances are crucial: knowing the conjugate acids and bases' influence allows us to predict the acidity or basicity of solutions. Ultimately, acidity ranking offers insight into the relative strength and nature of various solutions.

• Most Basic: KF
• Less Basic: HCOOK
• Neutral: NaNO_3
• More Acidic: HCOONH_4
• Most Acidic: NH_4Br

Conjugate Acids and Bases

Conjugate acids and bases are pairs born from the loss or gain of protons (H^+). They play a vital role in determining the characteristics of a solution.

When a weak base like NH_3 picks up a proton, it becomes NH_4^+, its conjugate acid. This new species can donate protons in water, leading to increased acidity. Conversely, HF, a weak acid, loses a proton to form F^- (the conjugate base), which leans towards basicity by accepting protons.

This see-saw action helps in predicting the acidity or basicity of salts. The conjugate acid (NH_4^+) will significantly contribute to a solution's acidity if formed from a weak base. Meanwhile, the conjugate base (F^-) will move the needle towards basicity if formed from a weak acid. Understanding these interactions unveils the complex nature of chemical solutions.

• Conjugate Acid: +H⁺ uptake (e.g., NH_4⁺)
• Conjugate Base: -H⁺ loss (e.g., F^-)