Question

Identify the following solutions as acidic or basic, estimate \(\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]\) and \(\left[\mathrm{OH}^{-}\right]\) values for each, and rank them in order of increasing acidity: (a) Saliva, \(\mathrm{pH}=6.5\) (b) Pancreatic juice, \(\mathrm{pH}=7.9\) (c) Orange juice, \(\mathrm{pH}=3.7\) (d) Wine, \(\mathrm{pH}=3.5\)

Short answer

Order of increasing acidity: Pancreatic juice, Saliva, Orange juice, Wine.

Step-by-step solution

Determine Acidity or Basicity

To identify if the solution is acidic or basic, compare the pH to 7. If the pH < 7, the solution is acidic. If the pH > 7, the solution is basic.

Calculate \([\mathrm{H}_3\mathrm{O}^+]\)

Use the formula \([\mathrm{H}_3\mathrm{O}^+] = 10^{-\text{pH}}\) to calculate the hydronium ion concentration for each solution. For example, for saliva with \(\text{pH} = 6.5\), \([\mathrm{H}_3\mathrm{O}^+] = 10^{-6.5}\).

Calculate \([\mathrm{OH}^-]\)

Use the relationship \( [\mathrm{H}_3\mathrm{O}^+][\mathrm{OH}^-] = 10^{-14} \) to find the hydroxide ion concentration. Rearrange to find \([\mathrm{OH}^-] = \frac{10^{-14}}{[\mathrm{H}_3\mathrm{O}^+]}\). Calculate this for each solution.

Rank Solutions by Increasing Acidity

Rank the solutions by comparing their pH. The lower the pH, the higher the acidity. Order them accordingly.

Key concepts

Acidic and Basic Solutions

The acidity or basicity of a solution is determined by its pH level. The pH scale ranges from 0 to 14 and indicates how acidic or basic a solution is. A pH of 7 is neutral, like pure water.

• If the pH is less than 7, the solution is acidic. This means it has a higher concentration of hydronium ions (\(\mathrm{H}_3\mathrm{O}^{+}\)).
• If the pH is greater than 7, the solution is basic, implying a higher concentration of hydroxide ions (\(\mathrm{OH}^{-}\)).

For example, a solution with a pH of 3.5, like wine, is acidic. This helps us understand how chemicals interact in different environments.
Recognizing whether a solution is acidic or basic is crucial not only in chemistry labs but also in various real-life applications such as cooking, cleaning, and even skincare.

Hydronium Ion Concentration

Understanding hydronium ion concentration is key to determining a solution's acidity. The concentration of hydronium ions in a solution can be calculated using the formula: \[[\mathrm{H}_3\mathrm{O}^{+}] = 10^{-\text{pH}}\] This formula shows the exponential relationship between pH and \(\mathrm{H}_3\mathrm{O}^{+}\) concentration.

• A lower pH means a higher concentration of hydronium ions, indicating stronger acidity.
• For saliva with a pH of 6.5, the concentration would be \(10^{-6.5}\), illustrating mild acidity.

This calculation helps us predict how acidic a solution is, enabling us to compare it to others. It’s a straightforward way to rank solutions by acidity.

Hydroxide Ion Concentration

The hydroxide ion concentration provides insight into a solution's basicity. To find this concentration, the relationship between hydronium and hydroxide ions is used: \[[\mathrm{H}_3\mathrm{O}^{+}][\mathrm{OH}^{-}] = 10^{-14}\] To calculate \([\mathrm{OH}^{-}]\), rearrange the formula: \[[\mathrm{OH}^{-}] = \frac{10^{-14}}{[\mathrm{H}_3\mathrm{O}^{+}]}\] This allows us to find how basic the solution is:

• If a solution is basic, \([\mathrm{OH}^{-}]\) will be higher than \([\mathrm{H}_3\mathrm{O}^{+}]\).
• In solutions like pancreatic juice, with a pH of 7.9, this results in a higher \([\mathrm{OH}^{-}]\).

Calculating \([\mathrm{OH}^{-}]\) is essential for understanding the alkaline properties and potential reactivity of a solution.