Three metal samples of magnesium, aluminium and iron were taken and rubbed with sand paper. These samples were then put separately in test tubes containing dilute hydrochloric acid. Thermometers were also suspended in each test tube so that their bulbs dipped in the acid. The rate of formation of bubbles was observed. The above activity was repeated with dilute nitric acid and the observations were recorded. Answer the following questions : (a) When activity was done with dilute hydrochloric acid, then in which one of the test tubes was the rate of formation of bubbles the fastest and the thermometer showed the highest temperature ? (b) Which metal did not react with dilute hydrochloric acid ? Give reason. (c)(i) Why is hydrogen gas not evolved when a metal reacts with dilute nitric acid ? Name the ultimate products formed in the reaction. (c)(ii) Name the type of reaction on the basis of which reactivity of metals is decided. You have two metals X and Y. How would you decide which is more reactive than the other ?

ScienceCBSE Class 10 · Board exam 2024, set 31/4/1 · 4 marks · Case-based

CBSE Class 10 Science 2024: question 37

Set in the CBSE Class 10 board exam of 2024, paper 31/4/1, section E, question 37, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q37 · 4 marks · Case-basedCompetency-basedMetals and Non-metals

Three metal samples of magnesium, aluminium and iron were taken and rubbed with sand paper. These samples were then put separately in test tubes containing dilute hydrochloric acid. Thermometers were also suspended in each test tube so that their bulbs dipped in the acid. The rate of formation of bubbles was observed. The above activity was repeated with dilute nitric acid and the observations were recorded.

Answer the following questions :

(a)
When activity was done with dilute hydrochloric acid, then in which one of the test tubes was the rate of formation of bubbles the fastest and the thermometer showed the highest temperature ?
1 mark
(b)
Which metal did not react with dilute hydrochloric acid ? Give reason.
1 mark
(c)(i)
Why is hydrogen gas not evolved when a metal reacts with dilute nitric acid ? Name the ultimate products formed in the reaction.
2 marks
OR
(c)(ii)
Name the type of reaction on the basis of which reactivity of metals is decided. You have two metals X and Y. How would you decide which is more reactive than the other ?
2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/4/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Recall the order of Mg, Al and Fe in the reactivity series.

Hint 2

Where does hydrogen lie in the series compared with these three metals?

Hint 3

For nitric acid, think about what an oxidising agent does to hydrogen. For comparing X and Y, think about which metal can push the other out of its salt solution.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

(a) In the test tube containing magnesium. Magnesium is the most reactive of the three metals, so it gives hydrogen bubbles fastest and releases the most heat.
1 mark
(b) None. Magnesium, aluminium and iron all react with dilute HCl, because all three are more reactive than hydrogen and lie above it in the reactivity series. Iron reacts the slowest. (Credit is also given for naming a less reactive metal such as copper, which lies below hydrogen and cannot displace it from the acid.)
1 mark
(c)(i) Dilute nitric acid is a strong oxidising agent. It oxidises the hydrogen produced to water, so no hydrogen gas is released.
1 mark
(c)(i) The ultimate products are water and oxides of nitrogen (N $_{2}$ O, NO or NO $_{2}$ ), along with the metal nitrate. (Exception: Mg and Mn give H $_{2}$ with very dilute HNO $_{3}$ .)
1 mark
(c)(ii) Reactivity of metals is decided by displacement reactions.
1 mark
(c)(ii) Dip metal X in a solution of a salt of Y.
- If X displaces Y (Y gets deposited or the solution changes colour), then X is more reactive than Y.
- If no change occurs, Y is more reactive. You can confirm this by dipping Y in a salt solution of X, where Y will displace X.
Example: $Fe(s) + CuSO_{4} (aq) \to FeSO_{4} (aq) + Cu(s)$ , so Fe is more reactive than Cu.
1 mark

Answer: (a) Magnesium; (b) none – all three are above hydrogen in the reactivity series; (c)(i) HNO₃ is a strong oxidiser and oxidises H₂ to water; products: water and oxides of nitrogen; (c)(ii) displacement reaction – X is more reactive if it displaces Y from Y's salt solution

Where the marks are

Magnesium (1 mark)
All three react because they are more reactive than hydrogen (1 mark)
HNO₃ is a strong oxidising agent and oxidises H₂ to H₂O (1 mark)
Products: water and oxides of nitrogen (1 mark)
Displacement reaction (1 mark)
Correct test: a metal that displaces the other from its salt solution is more reactive (1 mark)

Revise the chapter

Chapter: Metals and Non-metals (notes, formulas, where marks are lost and every past question)

Practise this chapterBoard-style questions from Metals and Non-metals, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 31/4/1: every question, by section.

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CBSE Class 10 Science 2024: question 37

Hints

Step-by-step solution

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