Asked by tyrone
Which of the following elements will react with water and turn phynolpthalene pH indicater to pink?
a
Mg, K and Al
b
Li, Na and Al
c
Cl, N and Al
d
Mg, K and Ca
All Answers 1
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Answer: d) Mg, K and Ca.
Reason: Phenolphthalein turns pink in basic solution (OH− present). Alkali metals (K) and many alkaline-earth metals (Ca, and to a lesser extent Mg) react with water to give hydroxides and H2. K and Ca react readily; Mg reacts slowly with cold water (more with hot water) to give Mg(OH)2, which is basic. Aluminum does not react with water under normal conditions because of its protective oxide layer, so options containing Al are not correct.
Reason: Phenolphthalein turns pink in basic solution (OH− present). Alkali metals (K) and many alkaline-earth metals (Ca, and to a lesser extent Mg) react with water to give hydroxides and H2. K and Ca react readily; Mg reacts slowly with cold water (more with hot water) to give Mg(OH)2, which is basic. Aluminum does not react with water under normal conditions because of its protective oxide layer, so options containing Al are not correct.
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