Case Study:

Riya loved eating oranges during the summer season. One afternoon, she ate nearly 6 oranges while studying. After some time, she noticed a sharp burning sensation in her mouth and around her teeth. Even cold water felt uncomfortable. Her mother suggested brushing her teeth gently with toothpaste. Within a few minutes, the burning feeling reduced significantly.

Curious about this, Riya searched online and learned that oranges contain citric acid, which is a weak acid naturally present in citrus fruits.

If you're finding it tricky to tell your acids from your bases, check out these simple tips to identify acids, bases, and salts to master the basics.

Eating too many acidic foods can temporarily increase the acidity inside the mouth. This may irritate the soft tissues and make the teeth feel sensitive. Most toothpastes contain mild basic substances such as calcium carbonate or sodium bicarbonate. These substances help neutralise the extra acid present in the mouth.

Riya also observed that the toothpaste packet mentioned a “pH balancing formula.” Her science teacher explained that when an acid reacts with a base, a neutralisation reaction takes place.

Neutralisation isn't just for toothpaste; you can see the science behind lemon juice and baking soda right in your kitchen!

In this reaction, the acidic effect decreases, helping the mouth return closer to a normal pH level.

To test this idea, Riya compared two situations. On one day, she rinsed her mouth only with water after eating oranges, and the discomfort lasted for almost 20 minutes. On another day, she brushed with toothpaste, and the discomfort reduced within 5 minutes. This simple observation helped her connect daily life with the concept of acids, bases, and neutralisation reactions.

CASE-BASED QUESTIONS

 MCQ 

Q1. Which acid present in oranges mainly causes the sharp sensation in the mouth?
A. Hydrochloric acid
B. Citric acid
C. Acetic acid
D. Sulphuric acid

Q2. Toothpaste reduces the burning feeling mainly because it:
A. increases acidity in the mouth
B. removes all bacteria instantly
C. contains mild bases that neutralise acids
D. changes acid into sugar

 Assertion–Reason 

Q3. Assertion (A): Toothpaste helps reduce the burning sensation after eating many oranges.
Reason (R): Toothpaste contains mild basic substances that react with excess acids in the mouth.
A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.

 Application-Based  

Q4. A student eats many lemons and immediately feels irritation in the mouth. Which household substance would most likely help reduce the irritation?
A. Vinegar
B. Baking soda solution
C. Lemon juice
D. Soft drink

Q5. Why did the discomfort last longer when Riya rinsed only with water instead of brushing with toothpaste?

 Data/Logic-Based 

Q6. Riya recorded the following observations:

Based on the data, what can be concluded about toothpaste?
A. Toothpaste increases acidity in the mouth.
B. Toothpaste slows down neutralisation.
C. Toothpaste helps neutralise excess acid more effectively than water.
D. Water is more basic than toothpaste.

 Application + Reasoning  

Q7. Explain how the concept of neutralisation reaction is involved when toothpaste is used after eating acidic fruits.

Before checking the answers, why not test your skills? You can grab a Chemistry worksheet or challenge yourself with an unsolved practice paper to see where you stand.

ANSWER KEY WITH EXPLANATION

A1. B. Citric acid
Explanation: Citric acid is naturally present in citrus fruits like oranges and lemons. It increases acidity in the mouth, causing temporary irritation and sensitivity.

A2. C. contains mild bases that neutralise acids
Explanation: Toothpaste contains mild bases such as calcium carbonate or sodium bicarbonate. These react with excess acid through a neutralisation reaction.

A3. A. Both A and R are true, and R is the correct explanation of A.
Explanation: The reason correctly explains the assertion. Toothpaste reduces acidity because bases neutralise acids according to the NCERT concept of neutralisation reaction.

A4. B. Baking soda solution
Explanation: Baking soda is basic in nature. It can help neutralise excess acid present in the mouth and reduce irritation.

A5. Water only dilutes the acid, but toothpaste contains mild bases that chemically neutralise the acid. Therefore, brushing with toothpaste reduces discomfort faster.

A6. C. Toothpaste helps neutralise excess acid more effectively than water.
Explanation: The data shows that discomfort reduced much faster with toothpaste. This indicates that neutralisation occurred more effectively in the presence of a base.

A7. Acidic substances from oranges increase acidity in the mouth. Toothpaste contains mild bases that react with the acids and reduce their effect through a neutralisation reaction.

If you want to see how a topper structures their answers, take a look at our solved practice papers for more inspiration.

 Ready to ace your boards?  Practice these top 10 exam questions on acids and bases to see how well you know the chapter.

HOTS EXTENSION QUESTIONS

Q1. If a toothpaste company increases the amount of basic substance too much, could it create problems inside the mouth? Explain your reasoning.

Q2. Suppose a student frequently consumes acidic soft drinks and never brushes properly. Predict how this habit may affect tooth enamel over time using the concept of acids and bases.