Question

A new well is discovered in West Texas with a bicarbonate concentration of \(225 \mathrm{ppm}\). According to the line of best fit, which of the following best approximates the \(\mathrm{pH}\) of the well water? A) \(7.1\) B) \(7.3\) C) \(7.4\) D) \(8.4\)

Short answer

The best approximation for the pH of the well water with a bicarbonate concentration of 225 ppm is: C) 7.4

Step-by-step solution

Analyze the Answer Choices

Upon examining the answer choices, we notice that they are all clustered around a pH value of 7, which is considered neutral on the pH scale. This observation suggests that the well water is likely to have a pH close to, but not exactly at, neutrality. It may be slightly acidic (below 7) or slightly basic (above 7).

Consider the Relationship Between Bicarbonate Concentration and pH

Bicarbonate (\(HCO_3^-\)) is the conjugate base of carbonic acid (\(H_2CO_3\)). When bicarbonate concentration increases in water, this tends to increase the pH of the water, making it more basic. This relationship is governed by the following equilibrium reaction: \[H_2CO_3\rightleftharpoons H^+ + HCO_3^-\] Since the water has a bicarbonate concentration of 225 ppm, we can expect that increasing bicarbonate will result in an increase in pH, moving away from the neutral value of 7.

Estimate the Best Approximation for the pH

Knowing that the pH is likely to be above 7 due to the presence of bicarbonate, we can eliminate choices A and B, leaving us with the two most plausible options, C and D: C) 7.4 D) 8.4 Since the line of best fit was not explicitly given, we cannot make an accurate calculation, but we can still make an informed choice. Given that the bicarbonate concentration, while significant, is not very high, we can hypothesize that the well water's pH would not increase dramatically away from neutrality. Therefore, we can reasonably estimate that the best approximation for the pH of the well water is option C, 7.4.

Choose the Best Approximation for the pH

Based on our reasoning, we can conclude that the best approximation for the pH of the well water with a bicarbonate concentration of 225 ppm is: C) 7.4

Key concepts

Acid-Base Equilibrium

In chemistry, the concept of acid-base equilibrium is essential for understanding chemical reactions in water. Essentially, this equilibrium occurs when an acid and its conjugate base are present in a solution. The equilibrium can be represented with the general chemical equation: \[ HA ightleftharpoons H^+ + A^- \] In this reaction, \(HA\) is the acid, and \(A^-\) is its conjugate base. During equilibrium, acids donate hydrogen ions, \(H^+\), while bases accept them. This process maintains a balance between the concentration of acid and base in the solution.

• A strong acid completely ionizes in water, shifting the equilibrium towards the right.
• A weak acid only partially ionizes, indicating more molecules remain un-ionized, with equilibrium favoring the left.

Understanding equilibrium helps clarify why the pH of the solution changes in the presence of certain ions, like bicarbonate in water.

pH Scale

The pH scale is a measure of how acidic or basic a solution is. It ranges from 0 to 14, with 7 considered neutral.

• pH less than 7 indicates an acidic solution.
• pH greater than 7 indicates a basic, or alkaline, solution.
• Each unit change in pH represents a tenfold change in hydrogen ion concentration.

The pH is determined using the formula: \[ \text{pH} = -\log[H^+] \] Where \([H^+]\) is the concentration of hydrogen ions in the solution. With the bicarbonate concentration in the well water, it influences the solution's acidity and thus its pH, reflecting this scale.

Bicarbonate Concentration

Bicarbonate, \(HCO_3^-\), plays a significant role in water chemistry, particularly in buffering water and influencing its pH. The presence of bicarbonate in solution comes from the dissolution of carbon dioxide in water, forming carbonic acid, which then dissociates: \[ H_2O + CO_2 \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^- \] The bicarbonate serves as a conjugate base, balancing the pH by neutralizing added acids. This helps maintain a stable pH in natural waters. Some important aspects of bicarbonate in water include:

• Acts as a buffer, preventing drastic pH changes.
• Increased bicarbonate typically raises the pH, shifting water towards a more basic state.

In the West Texas well, the bicarbonate concentration of 225 ppm indicates that the water will likely have a pH above neutral, contributing to its assessment as a mild basic environment.

Water Chemistry

Water chemistry is a branch of chemistry that studies the composition and behavior of chemicals in aquatic environments. Water, being a universal solvent, dissolves a variety of substances, influencing its pH, hardness, and overall chemical properties.

• Hydrogen bonding in water leads to unique properties, such as high heat capacity and surface tension.
• Dissolution of salts and ions is critical for aquatic life and ecosystem health.

When considering water from a newly discovered well, parameters like bicarbonate concentration become key elements in understanding water quality.

Factors affecting water chemistry can include:
• Natural occurrences like mineral dissolution.
• Human activities such as pollution and water treatment.

In essence, examining aspects like bicarbonate concentration in well water aids in determining its chemical properties and potential uses.