Acids, Bases, and pH Quiz

Grade 7 · Science · Quiz

10-question quiz on acid and base properties, the pH scale, indicators, and neutralization.

Questions

Which of the following is an acid?
1. Baking soda
2. Soap
3. Lemon juice
4. Bleach
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Answer: Lemon juice
Lemon juice contains citric acid and has a pH of about 2–3. Baking soda, soap, and bleach are all bases with pH above 7.
Bases feel slippery and taste bitter.
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Answer: True
Bases have OH⁻ ions that react with skin oils, creating a slippery feel. The bitter taste is another common property (though you should never taste unknown chemicals).
A substance with a pH of 9 is classified as a ___.
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Answer: base
Any pH above 7 is basic (alkaline). pH 9 is moderately basic — similar to baking soda or seawater.
What color does litmus paper turn in a basic solution?
1. Red
2. Yellow
3. Blue
4. Green
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Answer: Blue
Bases turn red litmus paper BLUE. In acid, litmus turns red. The color change is used to identify whether an unknown solution is acidic or basic.
The lower the pH number, the stronger the base.
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Answer: False
Lower pH numbers indicate stronger acids. The higher the pH (above 7), the stronger the base. pH 14 is the strongest base on the standard scale.
Neutralization always produces:
1. Only water
2. Only a salt
3. A salt and water
4. An acid and a base
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Answer: A salt and water
The neutralization reaction always produces a salt (ionic compound) and water. The specific salt depends on which acid and base reacted.
Pure water has a pH of ___.
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Answer: 7
Pure water has exactly equal concentrations of H⁺ and OH⁻ ions, giving a pH of exactly 7 — the definition of neutral.
Your stomach produces hydrochloric acid to help digest food.
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Answer: True
The stomach lining secretes HCl (hydrochloric acid) to create an acidic environment (pH ~1.5–2) that activates digestive enzymes and kills ingested bacteria.
A pH of 2 compared to a pH of 4 means the pH 2 solution is:
1. 2 times more acidic
2. 10 times more acidic
3. 100 times more acidic
4. The same acidity
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Answer: 100 times more acidic
Because the pH scale is logarithmic (base 10), a 2-unit difference = 10 × 10 = 100× difference in acidity. pH 2 is 100× more acidic than pH 4.
An antacid relieves heartburn by:
1. Adding more acid to the stomach
2. Neutralizing excess stomach acid
3. Absorbing water in the stomach
4. Converting acid to a gas
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Answer: Neutralizing excess stomach acid
Antacids contain bases (like calcium carbonate or magnesium hydroxide) that react with excess HCl in the stomach through neutralization, reducing acidity and relieving heartburn.

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