Neutralisation reactions worksheet - Lasec Education News ... - Free Printable

Let’s go step by step to solve this worksheet.

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Part 1: Observations when acid (vinegar) is mixed with different substances

We’re told that vinegar is the acid, and we’re adding universal indicator plus another substance. Universal indicator changes color depending on whether something is acidic, neutral, or basic — but since we’re already adding acid (vinegar), the solution will start off acidic (probably red/orange). The key is to think about what happens when you add common household substances to vinegar + indicator.

Common substances used in neutralisation experiments with vinegar include:
- Baking soda (sodium bicarbonate) → fizzes, turns green/blue as it neutralises
- Soap or detergent → might turn greenish if slightly basic
- Lemon juice → still acidic, so stays red/orange
- Water → dilutes, may lighten color but still acidic
- Milk → slightly acidic, no big change
- Toothpaste → often basic, could turn green/blue

But since this is a school experiment, they likely expect common lab-style answers. Let’s pick three typical ones:

a) Baking soda (sodium bicarbonate)
Observation: Fizzing/bubbling occurs. Color changes from red/orange to green or blue as the acid is neutralised.

b) Soap solution
Observation: No fizzing. Color may change slightly toward green if soap is basic, but not dramatic.

c) Water
Observation: No reaction. Color remains red/orange (still acidic), maybe lighter shade due to dilution.

*(Note: These are reasonable expected observations for a middle/high school level.)*

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Research part: What happens in a neutralisation reaction?

Neutralisation = acid + base → salt + water

In terms of ions:
- Acids release H⁺ ions (hydrogen ions)
- Bases release OH⁻ ions (hydroxide ions)
- When they mix, H⁺ + OH → H₂O (water)
- The leftover ions form a salt

So, a neutral solution forms when the number of H⁺ ions equals the number of OH⁻ ions — they cancel each other out to make water, leaving behind dissolved salt ions that don’t affect pH much.

Example:
HCl + NaOH → NaCl + H₂O
H⁺ + Cl⁻ + Na⁺ + OH⁻ → Na⁺ + Cl⁻ + H₂O
Net: H⁺ + OH → H₂O

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Part 2: Complete the word equation

Ethanoic acid + sodium bicarbonate → sodium ethanoate + ? + ?

This is an acid + carbonate/bicarbonate reaction.

General rule:
Acid + Carbonate/Bicarbonate → Salt + Water + Carbon Dioxide

So here:
Ethanoic acid (CH₃COOH) + Sodium bicarbonate (NaHCO₃) → Sodium ethanoate (CH₃COONa) + Water (H₂O) + Carbon dioxide (CO₂)

You can see bubbles (CO₂ gas) during the reaction — that’s why baking soda and vinegar fizz!

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Final Answer:

1.
a) Acid (vinegar) + universal indicator + baking soda
Observation: Fizzing occurs; color changes from red/orange to green or blue.

b) Acid (vinegar) + universal indicator + soap solution
Observation: No fizzing; color may turn slightly green if soap is basic.

c) Acid (vinegar) + universal indicator + water
Observation: No reaction; color stays red/orange, possibly lighter.

Neutralisation process:
When an acid and a base react, hydrogen ions (H⁺) from the acid combine with hydroxide ions (OH⁻) from the base to form water (H₂O). The remaining ions form a salt. A neutral solution results when all H⁺ and OH⁻ ions have reacted completely, leaving only salt and water.

2. Ethanoic acid + sodium bicarbonate → sodium ethanoate + water + carbon dioxide