Question

The \(\mathrm{pH} 0.1 \mathrm{M}\) solution the following salts increases in the order: (a) \(\mathrm{NaCl}<\mathrm{NH}_{4} \mathrm{Cl}<\mathrm{NaCN}<\mathrm{HCl}\) (b) \(\mathrm{HCl}<\mathrm{NH}_{4} \mathrm{Cl}<\mathrm{NaCl}<\mathrm{NaCN}\) (c) \(\mathrm{NaCN}<\mathrm{NH}_{4} \mathrm{Cl}<\mathrm{NaCl}<\mathrm{HCl}\) (d) \(\mathrm{HCl}<\mathrm{NaCl}<\mathrm{NaCN}<\mathrm{NH}_{4} \mathrm{Cl}\)

Short answer

Option (b) is correct: HCl < NH₄Cl < NaCl < NaCN.

Step-by-step solution

Understand pH Scale

The pH scale is a measure of how acidic or basic a solution is, ranging from 0 to 14. A pH less than 7 indicates an acidic solution, a pH of 7 is neutral, and a pH greater than 7 is basic. Low pH indicates a high concentration of hydrogen ions (H⁺).

Classify Each Salt

Identify what type of solution each salt creates. - HCl is a strong acid, so it will have a very low pH. - NaCl is a neutral salt resulting from a strong acid and a strong base, maintaining a neutral pH. - NH4Cl is an acidic salt as it is the resultant of a weak base (NH₃) and a strong acid (HCl), so it will have a lower pH. - NaCN is a basic salt, resulting from a strong base (NaOH) and a weak acid (HCN), leading to a higher pH due to the production of OH⁻ ions.

Order the Salts by pH

Rank the solutions based on their expected pH values starting from acidic to basic. - HCl will have the lowest pH since it is the strongest acid. - NH₄Cl follows as it produces an acidic solution. - NaCl will be neutral, having a pH around 7. - NaCN will have the highest pH as it creates a basic solution.

Match to Given Options

Compare the determined order of increasing pH (HCl < NH₄Cl < NaCl < NaCN) to the provided options and select the matching option.

Key concepts

pH Scale

The pH scale is a vital tool in chemistry used to determine the acidity or basicity of a solution. Think of it as a measuring stick that ranges from 0 to 14. This scale tells us how many hydrogen ions, or H⁺ ions, are lurking in a solution. When you see a pH of less than 7, it indicates an acidic environment, meaning there are plenty of hydrogen ions present. A pH of exactly 7 is neutral, which is what pure water registers. If the pH is greater than 7, the solution is basic, where hydroxide ions (OH⁻) are more prominent than hydrogen ions. Understanding the pH scale is essential, as it helps predict how substances will react in different environments.

Acidic and Basic Solutions

When we talk about acidic and basic solutions, we are referring to their ability to donate or accept hydrogen ions. Acidic solutions have a high concentration of hydrogen ions and are usually identified by their sour taste and ability to corrode metals. Examples of strong acids include hydrochloric acid (HCl). Basic solutions, on the other hand, have a higher concentration of hydroxide ions. These solutions are often bitter to taste and slippery to touch, like bleach or soap. Sodium hydroxide (NaOH) is a common strong base. Knowing the properties of these solutions can help you understand the behavior of acids and bases during chemical reactions.

Salt Solutions

Salts play a fascinating role in chemistry as they result from the neutralization reaction between acids and bases. Depending on the strength of the reactant acids and bases, salts can produce solutions that are acidic, basic, or neutral.

• When a strong acid reacts with a strong base, the resulting salt, like NaCl, is neutral and doesn't alter the pH of water substantially.
• A strong acid and a weak base produce an acidic salt, such as NH₄Cl, which can lower the pH of a solution.
• Conversely, a weak acid with a strong base yields a basic salt like NaCN, which increases solution pH because it forms hydroxide ions.

Understanding salt solutions is key to predicting how different salts will affect the pH of a solution.

Chemical Classification

Classifying chemicals, particularly salts, helps us predict their behavior in solutions. These classifications are generally based on the acid-base properties of their constituent ions. Knowing which is the parent acid or base can help you determine if the resulting salt will make a solution acidic, neutral, or basic.

• Strong Acids like HCl create salts that may not greatly affect the pH.
• Weak Bases paired with strong acids, such as NH₃ with HCl, produce acidic salts.
• Strong Bases, when combined with weak acids like HCN, form basic salts such as NaCN.

This classification is a stepping stone for understanding how different salt solutions behave.

Hydrogen Ion Concentration

Hydrogen ion concentration is at the heart of understanding pH. It's essentially the amount of hydrogen ions (H⁺) in a solution, and it conveys how 'acidic' a solution is. This concentration is inversely related to pH: the higher the number of hydrogen ions, the lower the pH value. In acidic solutions like HCl, there's a large concentration of H⁺ ions which results in a very low pH. In contrast, solutions with fewer hydrogen ions, such as those containing basic salts like NaCN, result in a higher pH due to the presence of more hydroxide ions. Grasping this concept is crucial for solving problems related to solution acidity and basicity.