CBSE 2025 · Region 4 · Set 1 · Q27 · 3 marks
Why do we balance a chemical equation? Name and state the law that suggests the balancing of a chemical equation? Balance the following chemical equation : \[\mathrm{Zn}+\mathrm{H}_{3} \mathrm{PO}_{4} \rightarrow \mathrm{Zn}_{3}\left(\mathrm{PO}_{4}\right)_{2}+\mathrm{H}_{2} \]Define a precipitation reaction. Give its example and also express the reaction that occurs in the form of a balanced chemical equation.
Why do we balance a chemical equation? Name and state the law that suggests the balancing of a chemical equation? Balance the following chemical equation : \[\mathrm{Zn}+\mathrm{H}_{3} \mathrm{PO}_{4} \rightarrow \mathrm{Zn}_{3}\left(\mathrm{PO}_{4}\right)_{2}+\mathrm{H}_{2} \]
Define a precipitation reaction. Give its example and also express the reaction that occurs in the form of a balanced chemical equation.
Marking-scheme solution
(A)
The number of atoms of each element remains same before and after a chemical reaction / to satisfy the law of conservation of mass.
Law of conservation of mass.
Mass can neither be created nor destroyed in a chemical reaction.
\(\displaystyle 3 \mathrm{Zn}+2 \mathrm{H}_{3} \mathrm{PO}_{4} \longrightarrow \mathrm{Zn}_{3}\left(\mathrm{PO}_{4}\right)_{2}+3 \mathrm{H}_{2}\) OR
(B)
Any reaction in which a precipitate (insoluble substance) is formed is called a precipitation reaction.
Example: when sodium sulphate solution is added to the barium chloride solution a white precipitate of barium sulphate is formed.
\[\mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{BaCl}_{2}(\mathrm{aq}) \longrightarrow \underset{\mathrm{ppt}}{\mathrm{BaSO}_{4}}(\mathrm{~s})+2 \mathrm{NaCl}(\mathrm{aq})
\]
Chemical Reactions and EquationsWriting and Balancing Chemical EquationsApplyshort_answermedium
More from Chemical Reactions and Equations
- The main observations while performing the experiment of burning magnesium ribbon in air are: (i) Magnesium…2025 · asked 3×
- In which one of the following situations a chemical reaction does not occur?2025 · asked 3×
- The colour of the solution observed after about 1 hour of placing iron nails in copper sulphate solution is2025 · asked 3×
- Assertion: Silver chloride turns grey in sunlight. Reason (R): Decomposition of silver chloride into silver…2025 · asked 3×
- Assertion: Decomposition reactions are generally endothermic reactions. Reason (R): Decomposition of organic…2025 · asked 3×
- List the possible sources of energy required in decomposition reactions. Illustrate any one with a suitable…2025 · asked 3×
- Electrolysis of water is a decomposition reaction. The mass ratio (M H: M O) of hydrogen and oxygen gases…2025 · asked 3×
- The values of a, b, c and d in the following balanced chemical equation are respectively: a Pb(NO 3) 2 heat b…2025 · asked 3×
CBSE Class 10 Science past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.