Grade 7 Acids and Bases worksheet - Free Printable

Since you've uploaded an image of a worksheet titled "Investigating the pH Scale", I'll help you solve the task based on common knowledge of the pH values of everyday substances. This is a typical science activity where students explore how different substances fall on the pH scale.

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🔍 Guiding Question:

How does the pH scale qualitatively relate to acids and bases?

> The pH scale ranges from 0 to 14:
- pH < 7: Acidic
- pH = 7: Neutral
- pH > 7: Basic (alkaline)

Acids donate hydrogen ions (H⁺), while bases accept them or release hydroxide ions (OH⁻). The lower the pH, the stronger the acid; the higher the pH, the stronger the base.

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✔ Step 2: Fill in the Table with Approximate pH Values and Classify as Acid/Base

Here’s a completed version of the table based on real-world pH values:

| Substance | pH | Acid/Base |
|------------------|--------|-----------|
| Drain cleaner | 13–14 | Base |
| Hand soap | 9–10 | Base |
| Blood | 7.35–7.45 | Base |
| Spit | 6.5–7.5 | Neutral / Slightly basic |
| Milk | 6.5–6.7 | Slightly acidic |
| Chicken Soup | 6–7 | Slightly acidic |
| Coffee | 5 | Acidic |
| Orange Juice | 3–4 | Acidic |
| Soda Pop | 2.5–3.5 | Acidic |
| Vomit | 1–2 | Acidic |
| Battery Acid | 0–1 | Acidic |

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🧪 Explanation of Each Substance's pH:

- Drain cleaner: Strongly basic (high pH) due to chemicals like sodium hydroxide.
- Hand soap: Mildly basic (to help remove oils).
- Blood: Slightly basic (~7.4); tightly regulated by the body.
- Spit (saliva): Around neutral, but can vary slightly depending on diet.
- Milk: Slightly acidic due to lactic acid.
- Chicken soup: Close to neutral, but slightly acidic from ingredients.
- Coffee: Acidic due to organic acids like chlorogenic acid.
- Orange juice: Highly acidic because of citric acid.
- Soda pop: Very acidic due to carbonic acid and phosphoric acid.
- Vomit: Highly acidic (stomach acid = HCl, pH ~1–2).
- Battery acid: Extremely acidic (sulfuric acid).

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🔗 Step 3: Draw Lines from Substances to pH Scale

Now, draw lines from each substance in the table to its approximate position on the pH scale (0–14) shown below:

```
pH Scale:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
┌─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┐
│Red │Oran │Yell │Lime │Green│Green│Green│Green│Green│Teal │Blue │Blue │Blue │Purple│
└─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┘
acidic neutral alkaline
```

#### ➤ How to connect:
- Battery Acid → pH 0–1 → Left end (red)
- Vomit → pH 1–2 → Just right of battery acid
- Soda Pop → pH 2.5–3.5 → Between 2 and 4
- Orange Juice → pH 3–4 → Near 3–4
- Coffee → pH 5 → Middle of acidic range
- Chicken Soup → pH 6–7 → Near 6–7
- Milk → pH 6.5–6.7 → Just left of 7
- Spit → pH 6.5–7.5 → Around 7
- Blood → pH 7.35–7.45 → Just right of 7
- Hand Soap → pH 9–10 → Blue region
- Drain Cleaner → pH 13–14 → Far right (purple)

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✔ Final Answer Summary:

| Substance | pH Range | Classification |
|------------------|----------|----------------|
| Drain cleaner | 13–14 | Base |
| Hand soap | 9–10 | Base |
| Blood | 7.35–7.45| Base |
| Spit | 6.5–7.5 | Neutral/Basic |
| Milk | 6.5–6.7 | Acidic |
| Chicken Soup | 6–7 | Slightly acidic|
| Coffee | 5 | Acidic |
| Orange Juice | 3–4 | Acidic |
| Soda Pop | 2.5–3.5 | Acidic |
| Vomit | 1–2 | Acidic |
| Battery Acid | 0–1 | Acidic |

> 🔹 Conclusion:
The pH scale helps us classify substances as acidic, neutral, or basic. Most household items fall outside the neutral point (7), showing that many common substances are either acidic or basic. Understanding this helps explain why certain substances corrode metals (acids), clean grease (bases), or affect our health (e.g., stomach acid vs. blood pH).

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Let me know if you'd like a printable version or a diagram of the connections!