pH of Samples (Using pH Paper/Universal Indicator) MCQs Quiz | Class 10
This quiz on pH of Samples (Using pH Paper/Universal Indicator) is designed for Class X Science (Code 086), covering Unit I – Practicals. It includes questions on identifying the pH of dilute HCl, dilute NaOH, dilute ethanoic acid, lemon juice, water, and dilute hydrogen carbonate solution using pH paper or universal indicator. Test your knowledge and once done, submit your answers to see your score and download a detailed answer PDF.
Understanding pH: A Deep Dive into Acids, Bases, and Indicators
The pH scale is a fundamental concept in chemistry, allowing us to quantify the acidity or alkalinity of a solution. It ranges from 0 to 14, where values below 7 indicate acidity, 7 indicates neutrality, and values above 7 indicate alkalinity (basicity).
What is pH?
pH stands for “potential of hydrogen” and is a measure of the hydrogen ion (H+) concentration in a solution. A higher concentration of H+ ions means a lower pH and a more acidic solution. Conversely, a higher concentration of hydroxide (OH-) ions means a higher pH and a more basic solution.
How to Measure pH: pH Paper and Universal Indicator
To determine the pH of various samples, we commonly use pH paper or universal indicator solution. These are substances that change color depending on the pH of the solution they are exposed to.
- pH Paper: This is a strip of paper impregnated with a mixture of indicator dyes. When dipped into a solution, the paper changes color. This color is then compared to a standard pH color chart to estimate the pH value. It provides a quick and approximate pH reading.
- Universal Indicator: This is a solution of several pH indicators that exhibits a gradual change in color over a wide pH range (typically 1 to 14). It offers a more precise estimation of pH compared to simple pH paper due to its broader spectrum of color changes.
Exploring Common Samples and Their pH
Let’s examine the typical pH values and indicator responses for the samples covered in this quiz:
| Sample | Nature | Approximate pH | Universal Indicator Color |
|---|---|---|---|
| Dilute Hydrochloric Acid (HCl) | Strong Acid | 1-2 | Red |
| Dilute Sodium Hydroxide (NaOH) | Strong Base | 13-14 | Deep Violet/Blue |
| Dilute Ethanoic Acid | Weak Acid | 3-5 | Orange/Yellow |
| Lemon Juice | Weak Acid (Citric Acid) | 2-3 | Red/Orange |
| Distilled Water | Neutral | 7 | Green |
| Dilute Hydrogen Carbonate Solution | Weak Base | 8-9 | Blue-Green |
Key Takeaways for pH Measurement
- Strong acids have very low pH values (closer to 0), and strong bases have very high pH values (closer to 14).
- Weak acids and bases have pH values closer to 7, but still on their respective acidic or basic sides.
- Distilled water is neutral with a pH of 7.
- The color change of pH paper or universal indicator helps in identifying the nature of a solution and its approximate pH.
- Always compare the observed color with a standard color chart for accurate estimation.
Practice Questions for Further Learning
- If a solution turns pH paper dark red, what is its approximate pH and nature?
- Which of the following would turn universal indicator blue: vinegar, soap solution, or pure water?
- A student tests a solution and finds its pH to be 5. Is this solution acidic, basic, or neutral?
- What is the significance of the number 7 on the pH scale?
- Why is it important to use distilled water when performing pH experiments on unknown solutions?
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