Question

Predict the color of the methyl orange indicator in a solution that has a \(\mathrm{pH}\) of \(3.5\).

Short answer

The color of methyl orange indicator in a solution with a pH of 3.5 will be orange.

Step-by-step solution

Identify the pH given

The pH given in the problem is 3.5.

Determine the pH range for color change

For methyl orange, if the pH is less than 3.1 it will be red. If the pH is more than 4.4, it will be yellow. Between these values it will be in transition.

Predict the color of methyl orange

The pH given (3.5) falls into the transition range. Therefore, it will be in the transition between red and yellow, likely an orange color.

Key concepts

Acid-base Indicators

Acid-base indicators are substances that exhibit different colors at different pH levels, providing a visual representation of the acidity or basicity of a solution. They are typically weak acids or bases, which undergo a color change through a process known as dissociation or protonation, depending on the hydrogen ion concentration in the solution.

For instance, in the context of methyl orange, a common laboratory indicator, it changes color in response to the pH of the solution to which it's added. If you add a few drops of methyl orange to a highly acidic solution (pH below 3.1), it will appear red, signifying a low pH. On the other hand, in a basic or less acidic solution (pH above 4.4), it turns yellow, indicating a higher pH. Between these pH values, the indicator will be an intermediate color—in this case, orange, due to a partial association and dissociation of the indicator molecules.

When using indicators, it's important to choose one with a transition range that falls within the pH range of the expected color change. This ensures accuracy and ease of reading, particularly when conducting experiments or titrations in a chemistry lab.

pH Measurement

The pH scale is a quantitative measure of the acidity or basicity of an aqueous solution. It is defined by the negative logarithm of the hydrogen ion (\text{H}^+) concentration. Mathematically, it's expressed as \[ \mathrm{pH} = -\log[\text{H}^+] \.\]

The scale typically ranges from 0 to 14, with 7 being neutral. Values below 7 indicate acidity, while values above 7 suggest a basic or alkaline solution. pH measurement is essential in numerous fields, including chemistry, biology, medicine, and environmental science, to name a few. It's necessary for controlling the conditions in which chemical reactions occur, understanding enzyme activity in biochemistry, ensuring the safety and effectiveness of pharmaceuticals, and maintaining the ecological balance in water bodies.

To measure pH, one can use a pH meter, litmus paper, or an acid-base indicator like methyl orange. Each method has its advantages and limitations, though for immediate visual feedback, indicators are often preferred in educational settings and quick analyses.

Chemistry Color Change

Color changes in chemistry are often indicative of a chemical reaction taking place, with acid-base reactions being a prime example. These changes are frequently utilized in the use of indicators to signal the end point of a titration or the pH of a solution. The color change results when the chemical structure of a molecule is altered, usually by gaining or losing a proton (which is a hydrogen ion).

This chemical change affects the way the molecule absorbs and emits light, thus altering its color. For example, in methyl orange, the color change is attributed to the structural changes in the molecular ions due to pH alterations. Molecules with conjugated systems—alternating single and double bonds—are particularly prone to color changes as their electronic structures are sensitive to the presence of protons.

Transition Range and Color Indication

In an acid-base indicator like methyl orange, the color transition does not happen abruptly at a specific pH, but over a range of pH values. This is why understanding the transition range is key to interpreting indicator colors correctly. With a pH of 3.5, students would observe a color that is neither red nor yellow but orange, illustrating the gradual shift between the extremes, which occurs due to the mixture of different ion forms that are present at different pH levels.