The chemical reaction K2SO4 (aq.) + BaCl2 (aq.) → 2KCl (aq.) + BaSO4 (solid) is an example of :
- A.Addition reaction
- B.Displacement reaction
- C.Decomposition reaction
- D.Double displacement reaction
Correct answer
Explanation
The correct answer is D, Double displacement reaction. Potassium and barium exchange their partner ions: K₂SO₄ and BaCl₂ swap ions to give KCl and BaSO₄.
In a double displacement reaction two compounds exchange ions. Here the sulphate ion moves from potassium to barium, and the chloride ion moves from barium to potassium. Barium sulphate is insoluble in water, so it separates as a white solid; such a reaction is also called a precipitation reaction. The same type of reaction occurs when silver nitrate and sodium chloride solutions are mixed and white silver chloride settles.
A is wrong: an addition (combination) reaction joins two or more substances into a single product, while here two products form.
B is wrong: in a displacement reaction one element replaces another, as when iron displaces copper from copper sulphate; here two ions are exchanged.
C is wrong: a decomposition reaction breaks one compound into simpler substances, but this reaction starts with two compounds.
Exam tip: AB + CD → AD + CB is double displacement; a white precipitate of BaSO₄ is the standard test for sulphate ions.
Practice Questions
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1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
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- B.Only two
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- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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