Question:
Observe the following sequence of reactions and identify the correct statements about \(W\), \(X\) and \(Z\):
\[
Ca + O_2 \rightarrow X \xrightarrow{H_2O} Y \xrightarrow{CO_2} Z \xrightarrow{-H_2O} Z \xrightarrow{H_2O/\text{ excess }CO_2} W
\]
I. W is soluble in water
II. Z is used as mild abrasive in toothpaste
III. X is slaked lime
Observe the following sequence of reactions and identify the correct statements about \(W\), \(X\) and \(Z\):
\[
Ca + O_2 \rightarrow X \xrightarrow{H_2O} Y \xrightarrow{CO_2} Z \xrightarrow{-H_2O} Z \xrightarrow{H_2O/\text{ excess }CO_2} W
\]
I. W is soluble in water
II. Z is used as mild abrasive in toothpaste
III. X is slaked lime
Show Hint
Quick lime \(=\) \(CaO\), Slaked lime \(=\) \(Ca(OH)_2\), Limestone \(=\) \(CaCO_3\).
Updated On: Jun 18, 2026
- I, III only
- II, III only
- I, II only
- I, II, III
Show Solution
Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Concept:
Calcium undergoes a sequence of reactions leading to calcium oxide, calcium hydroxide, calcium carbonate and finally calcium bicarbonate. Knowledge of common names and properties of these compounds is essential.
Step 1: Identify \(X\).
Calcium burns in oxygen to form calcium oxide. \[ 2Ca + O_2 \rightarrow 2CaO \] Hence, \[ X=CaO \] which is known as quick lime.
Step 2: Identify \(Y\).
\[ CaO + H_2O \rightarrow Ca(OH)_2 \] Therefore, \[ Y=Ca(OH)_2 \] which is slaked lime.
Step 3: Identify \(Z\).
\[ Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \] Hence, \[ Z=CaCO_3 \] which is calcium carbonate.
Step 4: Identify \(W\).
In excess carbon dioxide and water, \[ CaCO_3 + CO_2 + H_2O \rightarrow Ca(HCO_3)_2 \] Thus, \[ W=Ca(HCO_3)_2 \] which is soluble in water.
Step 5: Check the statements.
Statement I: \[ Ca(HCO_3)_2 \] is soluble in water. Correct. Statement II: \[ CaCO_3 \] is used as a mild abrasive in toothpaste. Correct. Statement III: \(X\) is \(CaO\) (quick lime), not slaked lime. Incorrect. Therefore, \[ \boxed{\text{I and II only}} \]
Step 1: Identify \(X\).
Calcium burns in oxygen to form calcium oxide. \[ 2Ca + O_2 \rightarrow 2CaO \] Hence, \[ X=CaO \] which is known as quick lime.
Step 2: Identify \(Y\).
\[ CaO + H_2O \rightarrow Ca(OH)_2 \] Therefore, \[ Y=Ca(OH)_2 \] which is slaked lime.
Step 3: Identify \(Z\).
\[ Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \] Hence, \[ Z=CaCO_3 \] which is calcium carbonate.
Step 4: Identify \(W\).
In excess carbon dioxide and water, \[ CaCO_3 + CO_2 + H_2O \rightarrow Ca(HCO_3)_2 \] Thus, \[ W=Ca(HCO_3)_2 \] which is soluble in water.
Step 5: Check the statements.
Statement I: \[ Ca(HCO_3)_2 \] is soluble in water. Correct. Statement II: \[ CaCO_3 \] is used as a mild abrasive in toothpaste. Correct. Statement III: \(X\) is \(CaO\) (quick lime), not slaked lime. Incorrect. Therefore, \[ \boxed{\text{I and II only}} \]
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