Chemistry · Science General

Common Chemical Compounds and Reactions

1,204 Questions

Common chemical compounds and reactions questions test your knowledge of everyday chemicals, their formulas, and their interactions. Topics include properties of acids and bases, hard water chemistry, and compounds like baking soda and plaster of paris. This section is essential for general science preparation.

Acids and basesPlaster of parisHard water chemistryCommon chemical formulasEveryday chemical reactions

Common Chemical Compounds and Reactions Questions

Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

Sodium carbonate softens permanent hard water.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Sodium carbonate, $Na _2CO _3$ is also known as washing soda. It can remove temporary and permanent hardness from water. It is soluble in water and adds a large amount of carbonate ions to the water. These react with dissolved calcium and magnesium ions in the water to produce insoluble precipitates.

Hence, it is a true statement.
Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

Temporal hardness can be removed by just boiling the water because :

  1. Form salts

  2. Converts magnesium to soluble magnesium

  3. Converts carbonate to soluble carbonate

  4. Converts carbonate to insoluble carbonate
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Temporal hard water is caused by calcium bicarbonate. This hardness can be removed by just boiling the water, as this converts the carbonate to insoluble carbonate (This leaves a precipitate and can clog your boiler). 

Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

Calgon used as water softner is:

  1. $Na _2[Na _4(PO _3) _6]$
  2. $Na _4[Na _2(PO _3) _6] $
  3. $Na _2[Na _4(PO _4) _5]$

  4. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Calgon $\rightarrow { Na } _{ 6 }{ P } _{ 6 }{ O } _{ 18 }\rightarrow { Na } _{ 2 }\left[ { Na } _{ 4 }{ \left( { PO } _{ 3 } \right)  } _{ 6 } \right] $ it is used as water softener, when added to hard water following reaction takes place :

${ Na } _{ 6 }{ P } _{ 6 }{ O } _{ 18 }\rightarrow { 2Na }^{ + }+{ Na } _{ 4 }{ P } _{ 6 }{ O } _{ 18 }^{ 2- }$
${ Ca }^{ 2+ }+{ Na } _{ 4 }{ P } _{ 6 }{ O } _{ 18 }^{ 2- }\rightarrow { \left[ { Na } _{ 2 }{ Ca }{ P } _{ 6 }{ O } _{ 18 } \right]  }^{ 2- }+{ 2Na }^{ + }$

Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

In permanent hardness of water, when washing soda is treated with water, ________ is precipitated out.

  1. sodium carbonate

  2. magnesium carbonate

  3. calcium carbonate
  4. $Na _2CO _3 and\ MgCO _3$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The carbonate ions from sodium carbonate react with the calcium and magnesium ions in the water to produce insoluble product.

calcium ions + sodium carbonate → calcium carbonate + sodium ions

$Ca^{+2} + Na _2CO _3\rightarrow CaCO _3 + 2Na^+$

The water is softened because it no longer contains dissolved calcium ions and magnesium ions, hence we can say that it is converted in soft water. It will now form lather  easily with soap.

Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

Polyphosphates like sodium hexametaphosphate (calgon) are used as water softening agents because they:

  1. form soluble complexes with anionic species

  2. precipitate anionic species

  3. form soluble complexes with cationic species

  4. precipitate catatonic species.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 Polyphosphates like sodium hexametaphosphate (calgon) form souble complex with cations like $Ca^{2+}$ and  $Mg^{2+}  $present in hard water and hence are used as water softening agents.
$Na _{6}P _{6}O _{18} \rightarrow 2Na^{+}+ Na _{4}P _{6}O^{2-} _{18}$
$M^{2+} + Na _{4}P _{6}O^{2-} _{18}\rightarrow [Na _{2}MP _{6}O _{18}]^{2-} + 2Na^{+}$

Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

A water sample is said to contain permanent hardness if water contains:

  1. sulfates and chlorides of calcium and magnesium.

  2. carbonates of calcium and magnesium.

  3. bicarbonates of calcium and magnesium.

  4. sulfates and chlorides of sodium and potassium.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Permanent hardness of water is due to sulfates and chlorides of calcium and magnesium. Temporary hardness of water is due to bicarbonates of calcium and magnesium.
Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

Which of the following compounds is used for water softening?

  1. $Ca _3 (PO _4) _2$
  2. $Na _3PO _4$
  3. $Na _6 P _6O _18$
  4. $Na _2HPO _4$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Sodium hexametaphosphate $ (Na _6P _6O _{18}),$ commercially called 'calgon' is used for water softening. Calgon reacts with salts of $Ca/Mg$ (present in hard water) and forms inactive complex anions that do not precipitate in soap solution.