(a) Suggest one remedial measure each to counteract the change in pH in human beings in following cases: (i) Production of too much acid in stomach during indigestion (ii) Stung by a honey bee / nettle leaves (b) Fresh milk has a pH of 6. When it changes into curd will its pH increase or decrease? Why?

Q: (a) Suggest one remedial measure each to counteract the change in pH in human beings in following cases: (i) Production of too much acid in stomach during indigestion (ii) Stung by a honey bee / nettle leaves (b) Fresh milk has a pH of 6. When it changes into curd will its pH increase or decrease? Why?

### (a) Remedial Measures to Counteract pH Changes: * **(i) Production of too much acid in stomach during indigestion:** Take a mild base (antacid) such as **Milk of Magnesia** (magnesium hydroxide, $Mg(OH)_2$) or a mild solution of **baking soda** (sodium hydrogencarbonate, $NaHCO_3$). This neutralizes the excess hydrochloric acid produced in the stomach. * **(ii) Stung by a honey bee / nettle leaves:** * **Honey bee sting:** Apply a mild base like **baking soda paste** ($NaHCO_3$) to the affected area to neutralize the acidic sting. * **Nettle leaves sting:** Rub the affected area with the leaf of a **dock plant** (which is basic in nature) to neutralize the methanoic acid injected by the nettle hair. --- ### (b) pH Change of Milk into Curd: * **Observation:** The pH of milk will **decrease** (become less than 6). * **Reason:** When milk changes into curd, lactic acid is produced by the action of lactobacillus bacteria. The production of lactic acid increases the concentration of hydrogen ions ($H^+$ or $H_3O^+$) in the solution. Since pH is inversely related to hydronium ion concentration (higher hydronium ion concentration leads to a lower pH value), the pH decreases.

Acids, Bases and Salts

Importance of pH in Everyday Life

Official Answer

(a) Remedial Measures to Counteract pH Changes:

(i) Production of too much acid in stomach during indigestion:

Take a mild base (antacid) such as Milk of Magnesia (magnesium hydroxide, $Mg(OH)_2$ ) or a mild solution of baking soda (sodium hydrogencarbonate, $NaHCO_3$ ). This neutralizes the excess hydrochloric acid produced in the stomach.

(ii) Stung by a honey bee / nettle leaves:
Honey bee sting: Apply a mild base like baking soda paste ( $NaHCO_3$ ) to the affected area to neutralize the acidic sting.
Nettle leaves sting: Rub the affected area with the leaf of a dock plant (which is basic in nature) to neutralize the methanoic acid injected by the nettle hair.

(b) pH Change of Milk into Curd:

Observation: The pH of milk will decrease (become less than 6).
Reason: When milk changes into curd, lactic acid is produced by the action of lactobacillus bacteria. The production of lactic acid increases the concentration of hydrogen ions ( $H^+$ or $H_3O^+$ ) in the solution. Since pH is inversely related to hydronium ion concentration (higher hydronium ion concentration leads to a lower pH value), the pH decreases.

AntacidMilk of MagnesiaBaking sodaNeutralizeLactic acidpH decreasesHydronium ion concentration

Marking Scheme

1Part (a)(i): Suggesting a mild base/antacid like Milk of Magnesia or baking soda solution to neutralize stomach acid. (1 mark)
2Part (a)(ii): Suggesting a mild base (baking soda) for bee sting and dock plant leaf for nettle sting. (1 mark)
3Part (b): Stating that pH decreases because lactic acid is formed, increasing the concentration of $H^+$ ions. (1 mark)

Hint

Remember that acids have a pH less than 7, and as acidity increases, the pH value decreases. Neutralization requires a base to counteract an acid.

Quick Oral Answer

When milk turns to curd, its pH decreases because lactobacillus bacteria produce lactic acid, which increases the hydronium ion concentration.

Analysis & Explanation

Part (a) Analysis:

Stomach Acidity: The stomach produces hydrochloric acid ( $HCl$ ) to aid digestion. Overeating can trigger excess acid production, causing pain and irritation. Antacids, being basic, undergo a neutralization reaction:

$HCl(aq) + Mg(OH)_2(aq) \rightarrow MgCl_2(aq) + 2H_2O(l)$

Bee and Nettle Stings: Bee stings and nettle leaf hairs inject acidic toxins (like methanoic acid) into the skin. Applying a weak base neutralizes the acid, relieving pain.

Part (b) Analysis:

Fresh milk has a pH of $6.0$ (slightly acidic). As bacteria ferment lactose into lactic acid, the concentration of $H^+$ ions increases. According to the NCERT text, "Higher the hydronium ion concentration, lower is the pH value." Hence, the pH drops below $6$ , making the curd taste sour.

Common Mistakes

1Suggesting strong bases like sodium hydroxide ( $NaOH$ ) or potassium hydroxide ( $KOH$ ) for treating stings, which are highly corrosive and can cause severe chemical burns.
2Thinking that pH increases when milk turns to curd because curd is thicker, forgetting that acidity corresponds to a lower pH value.

Interesting Facts

Nature often provides remedies right next to the cause: dock plants, which are basic, frequently grow wild right next to acidic nettle plants.

Our stomach can tolerate a highly acidic pH of about 1.2 to 2.0 because of a protective mucus lining.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2023?

This question carries 3 marks in the CBSE Class 10 Science 2023 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Acids, Bases and Salts" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Importance of pH in Everyday Life" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2023 paper?

This is a Short Answer question from Section C in the CBSE Class 10 Science 2023 paper.