JSS 2: PH

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                              pH
pH stands for Potential of Hydrogen. It is defined as a measure of the degree of acidity or alkalinity of a solution. It is measured by an instrument called pH meter.
The pH scale ranges from 0 to 14; the lower and upper limits respectively.

pH Value Nature of Substance

0–6 Acidic
7 Neutral
8–14 Alkaline (Basic)


Examples

pH 1–2: Battery acid

pH 2–3: Lemon juice

pH 3–4: Vinegar

pH 6: Milk

pH 7: Pure water

pH 8: Sea water

pH 9–10: Baking soda solution

pH 12–13: Soap solution

pH 14: Sodium hydroxide solution


Indicators Used to Measure pH

1. Universal indicator


2. pH paper


3. pH meter


4. Litmus paper (shows whether a substance is acidic or alkaline but does not give the exact pH value)



Importance of pH

1. Helps determine whether a substance is acidic or alkaline.


2. Used in agriculture to test soil before planting crops.


3. Used in medicine to monitor body fluids.


4. Helps in water treatment and swimming pool maintenance.


5. Used in food and beverage production.


6. Important in chemical industries and laboratories.



Precautions

Handle strong acids and alkalis carefully.

Wear safety goggles and gloves during experiments.

Do not taste or directly smell chemicals.


Evaluation Questions

1. What is pH?


2. What is the range of the pH scale?


3. What pH value is considered neutral?


4. Name four substances and their approximate pH values.


5. Mention four uses of pH.



Assignment

1. Define pH.


2. Draw and label the pH scale from 0 to 14.


3. State the pH values for acidic, neutral, and alkaline substances.


4. Mention four indicators used to measure pH.


5. Explain five importance of pH in everyday life.



pH SCALE

The pH scale measures the acidity or alkalinity of a substance.

Acidic

Neutral

Basic

01234567891011121314

Strong acidNeutral waterStrong base

* 0–6: Acidic

* 7: Neutral

* 8–14: Basic (alkaline)
### 3\. INDICATORS

### Definition

Indicators are substances that change colour in acidic or basic solutions.

### Common Indicators

| Indicator | In Acid | In Base |
| --------------- | ---------- | ------- |
| Blue litmus | Red | Blue |
| Red litmus | Red | Blue |
| Methyl orange | Red | Yellow |
| Phenolphthalein | Colourless | Pink |

### Importance of Indicators

* Detect acids and bases.

* Determine the pH of substances.

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