Which of the following statements about universal indicator is/are true ? 1. It is a mixture of several indicators. 2. It shows different colours at different concentrations of hydrogen ions in solution. 3. It helps to determine the strength of given acid and base in titration. Select the correct answer using the code given below :
1, 2 and 3
Understanding Universal Indicators: Properties and Applications
Let's carefully examine each statement about universal indicators to determine which ones are true. Universal indicator is a common tool used in chemistry labs to estimate the pH of a solution.
Analysis of Statement 1: Universal Indicator is a Mixture of Several Indicators
This statement is accurate. A universal indicator is not a single substance but a blend of different acid-base indicators. Each individual indicator in the mixture changes color over a specific pH range. By combining several such indicators, the universal indicator can show a continuous range of colors across a wide pH spectrum, typically from highly acidic (pH 0-1) to highly alkaline (pH 13-14).
- Each component indicator has a distinct color change interval.
- The mixture exhibits a unique color for almost every whole number pH value on the scale.
Therefore, statement 1 is true.
Analysis of Statement 2: It Shows Different Colours at Different Concentrations of Hydrogen Ions in Solution
This statement is also correct. The color of a universal indicator is directly dependent on the pH of the solution it is in. The pH scale is defined by the concentration of hydrogen ions (\(H^+\)). A high concentration of \(H^+\) ions results in a low pH (acidic), while a low concentration of \(H^+\) ions (or high concentration of \(OH^-\) ions) results in a high pH (alkaline). Since the universal indicator displays different colors at different pH values, it consequently shows different colors at different hydrogen ion concentrations.
Here's a general idea of the color changes:
| pH Range | Acidity Level | Approximate Color |
|---|---|---|
| 0-3 | Strongly Acidic | Red/Orange |
| 4-6 | Weakly Acidic | Yellow/Green-Yellow |
| 7 | Neutral | Green |
| 8-10 | Weakly Alkaline | Blue/Indigo |
| 11-14 | Strongly Alkaline | Violet |
The color change directly reflects the \(H^+\) ion concentration. Thus, statement 2 is true.
Analysis of Statement 3: It Helps to Determine the Strength of Given Acid and Base in Titration
This statement requires a nuanced understanding. Universal indicators indicate the pH of a solution, and pH is related to the strength (and concentration) of an acid or base. A lower pH indicates a stronger acidic solution or a more concentrated acidic solution, and a higher pH indicates a stronger basic solution or a more concentrated basic solution. By showing the pH, the universal indicator can give an estimate of the strength or relative concentration.
However, in practical titration, universal indicators are generally not the preferred choice for determining the precise endpoint because their color change is gradual over a range of pH values, unlike the sharp color change seen with specific indicators (like phenolphthalein or methyl orange) at or near the equivalence point. Titration typically requires identifying a very specific point (the endpoint) where the reaction is complete, and a gradual color change makes this difficult to determine accurately.
That being said, the statement says it "helps" to determine the strength. By indicating the pH, it does provide information related to strength. For example, a solution showing red (pH 1-2) is clearly a stronger acid than one showing yellow (pH 5-6). So, while not precise for titration endpoints, it *can* help estimate strength via pH indication. Given the options and the likely intended meaning, this statement is considered true in the sense that it provides information related to strength by indicating pH.
Therefore, statement 3 is considered true in this context.
Conclusion
Based on the analysis of each statement:
- Statement 1: True
- Statement 2: True
- Statement 3: True
All three statements about universal indicator are true. Thus, the correct option is the one that includes 1, 2, and 3.
Revision Table: Key Properties of Universal Indicator
| Property | Description |
|---|---|
| Composition | Mixture of multiple pH indicators |
| pH Range Coverage | Wide range (typically 0-14) |
| Color Change | Shows different colors across the pH spectrum |
| Hydrogen Ion Dependency | Color changes based on \(H^+\) concentration (pH) |
| Usefulness | Estimating pH; rough indication of acid/base strength |
| Titration Use | Generally not for precise titration endpoints due to gradual change |
Additional Information: pH Scale and Indicators
The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It is defined as the negative logarithm (base 10) of the concentration of hydrogen ions:
\( \text{pH} = -\log_{10} [H^+] \)
Indicators are substances that change color in response to a change in pH. Single indicators usually have a narrow pH range over which they change color. Examples include:
- Litmus paper (red in acid, blue in base)
- Phenolphthalein (colorless in acid, pink in base, changes around pH 8.2-10)
- Methyl orange (red in acid, yellow in base, changes around pH 3.1-4.4)
A universal indicator combines the properties of several indicators to provide a broader range of color changes, making it useful for estimating pH across the entire scale.
Similar Questions
Which one of the following elements is used as a timekeeper in atomic clocks?
The valency of phosphorus is ________.
What is the number of moles of 'He' in 104 g of helium gas?
A mixture of sodium chloride (salt) and ammonium chloride can be separated by _________.
Very small insoluble particles in a liquid may be separated from it by using ________.
What is the number of atoms in 46 g of sodium-23 (N = Avogadro constant)?
The number of moles of oxygen gas used in the complete combustion of 1 mole of glucose is:
There are two elements - calcium (atomic number 20) and argon (atomic number 18). The mass number of both the elements is 40. They are therefore known as
Vitamin B 12 deficiency causes pernicious Anemia. Animals cannot synthesize vitamin B 12 . Humans must obtain all their vitaminB 12 from their diet. The complexing metal ion in vitamin B 12 is:
Which one of the following statements is NOT correct?
Important Questions from Basic Concepts of Chemistry
Which of the following pair is correct?
I. Isotopes – different mass numbers
II. Isobars – different atomic numbers
Which of the following is a zone of a flame?
I. Dark
II. Luminous
III. Non-Luminous
Sphalerite is an ore of:
If formula of sodium salt of an anion X is \(Na_2X\) , then the formula of its aluminium salt would be
Which of the following set contains same number of molecules?
A. 1 gram O 2, 2 grams SO 2
B. 1 gram CO 2, 1 gram N 2O
C. 1 gram O 2, 1 gram O 3
