Strong and weak acids/bases | Acids, bases, and salts | Chemistry | Khan Academy

Recent questions

• What is a strong acid?

  A strong acid is a substance that completely dissociates into its ions in a solution, meaning it releases all of its hydrogen ions (H+) when dissolved in water. This characteristic makes strong acids highly effective in chemical reactions, as they can significantly lower the pH of a solution. Common examples of strong acids include hydrochloric acid (HCl) and sulfuric acid (H2SO4). Understanding the behavior of strong acids is crucial in various scientific fields, including chemistry and biology, as they play a vital role in processes such as digestion and industrial applications. Their ability to fully dissociate contrasts with weak acids, which only partially dissociate in solution, leading to different properties and uses.

• How do acids affect molecules?

  Acids affect molecules primarily through their ability to donate protons (H+) in chemical reactions, which can lead to the breakdown or transformation of other substances. When an acid is introduced to a solution, it can interact with various molecules, altering their structure and properties. For instance, strong acids like hydrochloric acid can completely dissociate and react with organic compounds, leading to their decomposition. This process is essential in many chemical reactions, including those in biological systems, where acids can facilitate digestion and metabolic processes. Understanding how acids interact with molecules is fundamental in fields such as biochemistry, environmental science, and industrial chemistry.

• What is the difference between strong and weak acids?

  The primary difference between strong and weak acids lies in their ability to dissociate in solution. Strong acids, such as hydrochloric acid, completely dissociate into their ions, releasing all of their hydrogen ions (H+) and resulting in a low pH. In contrast, weak acids, like acetic acid, only partially dissociate, meaning that not all of their hydrogen ions are released into the solution, leading to a higher pH compared to strong acids. This distinction is crucial for understanding their behavior in chemical reactions, their applications in various industries, and their effects on biological systems. The strength of an acid influences its reactivity, safety, and the types of reactions it can participate in.

• Why is hydrochloric acid effective?

  Hydrochloric acid (HCl) is considered highly effective due to its strong acidic nature, which allows it to completely dissociate in solution, releasing a high concentration of hydrogen ions (H+). This property enables HCl to rapidly lower the pH of a solution, making it a powerful reagent in various chemical reactions. Its effectiveness is particularly notable in applications such as digestion, where it aids in breaking down food in the stomach, and in industrial processes, where it is used for cleaning metals and synthesizing chemicals. The speed at which HCl can disappear from a solution, often within about 10 minutes, further underscores its potency and utility in both laboratory and practical applications.

• How long does acetic acid take to dissociate?

  Acetic acid (CH3COOH) takes longer to dissociate compared to strong acids like hydrochloric acid. Specifically, it typically takes around 68 seconds for acetic acid to partially dissociate in solution. This slower dissociation rate is indicative of its classification as a weak acid, meaning that it does not fully release all of its hydrogen ions (H+) into the solution. The partial dissociation of acetic acid results in a more moderate pH change compared to strong acids. Understanding the dissociation time of acetic acid is important in various applications, including food preservation, where it is commonly used as a vinegar, and in biochemical processes, where its slower reaction rate can be beneficial.