Chemistry · Science General

Common Chemical Compounds and Reactions

1,197 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

Salts of calcium and magnesium like ___________ cause harness of water.

  1. bicarbonates

  2. chlorides

  3. sulphates

  4. phosphates
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation
Hard water is the water that contains soluble salts of bivalent ions like calcium and magnesium principally in the form of bicarbonates, chlorides, and sulfates. Water is softened on a small scale by the addition of phosphates, together with sodium carbonate (washing soda) which separates the calcium and magnesium as white precipitates of their respective phosphates.
Therefore option $A,\ B,\ C$ are correct
Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks

Temporary hardness maybe be removed from water by adding?

  1. $Ca(OH{ ) } _{ 2 }$
  2. $CaC{O } _{ 3 }$
  3. $CaS{O } _{ 4 }$
  4. $HCl$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

  • Temporary hardness is caused by dissolved calcium or magnesium hydrogencarbonate.

Some of the methods to remove hardness from water are:

  • Chemical Process of Boiling Hard Water
  • Adding Slaked Lime (Clark's Process)
  • Adding Washing Soda
  • Calgon Process
  • Ion Exchange Process
  • Using Ion Exchange Resins

Clark’s method: In this method calculated amount of lime is added to hard water. It precipitates out calcium carbonate and magnesium hydroxide which can be filtered off.
$Ca(HCO _3) _2+Ca(OH) _2 \rightarrow 2CaCO _3(\downarrow)+2H _2O$
$Mg(HCO _3) _2+Ca(OH) _2 \rightarrow 2CaCO _3(\downarrow)+Mg(OH) _2(\downarrow)+2H _2O$

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

Permanent hardness in water is due to the presence of:

  1. $Ca^{2+},\:Mg^{2+}$
  2. $CaCl _{2},\:MgCl _{2}$
  3. $CaCO _{3},\:MgCO _{3}$

  4. all of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Permanent hardness is caused by the presence of dissolved chlorides and sulfates of calcium and magnesium. Calcium and magnesium ions themselves (Option A) are the cause of both temporary and permanent hardness, but the specific chemical compounds responsible for permanent hardness are the salts like CaCl2 and MgCl2.

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

The reagent commonly used to determine hardness of water is:

  1. oxalic acid

  2. disodium salt of EDTA

  3. sodium citrate

  4. sodium thiosulphate
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Determination of hardness of water:

Determination of hardness of water is done by titration method using the technique of complexometric titration.    

Ethylenediamine tetra-acetic acid and its sodium salts (EDTA) form a chelated soluble complex when it is titrated against a solution containing certain metal cations that cause hardness to water.

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

Which one of the following process will produce hard water?

  1. Saturation of water with $MgCO _{3}$
  2. Saturation of water with $CaSO _{4}$
  3. Addition of $Na _{2}SO _{4}$ to water
  4. Saturation of water with $CaCO _{3}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Calcium sulfate $\left( CaS{ O } _{ 4 } \right) $ being less soluble in water causes permanent hardness in water.

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

In a sample of temporary hard water which of the following water softening process does NOT produced any precipitate of cation responsible for hardness ? 

  1. Boiling water

  2. Addition of lime water

  3. Addition of sodium hexameta phosphate

  4. Addition of sodium carbonate
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Temporary hardness is caused by bicarbonates of calcium and magnesium. Boiling water precipitates insoluble carbonates. Adding lime water precipitates calcium carbonate or magnesium hydroxide. Adding sodium carbonate precipitates calcium carbonate. However, adding sodium hexametaphosphate (Calgon's method) sequesters the calcium and magnesium ions into soluble complex anions without forming any precipitate of the hardness-causing cations.

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

In water:

  1. temporary hardness is due to the bicarbonates of $Ca^{2+}$ and $Mg^{2+}$.
  2. permanent hardness is due to chlorides and sulphates of $Ca^{2+}$ and $Mg^{2+}$.

  3. hardness can be removed by adding phosphates.

  4. all of the above.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Temporary hardness is indeed due to bicarbonates, permanent hardness is due to chlorides/sulfates, and phosphates are used in water softening processes (like Calgon).

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

In a laboratory, hard water, required for an experiment, is not available. However, the following salts are available in the school laboratory :
1. Sodium sulphate
2. Calcium sulphate
3. Magnesium chloride
4. Sodium chloride
5. Calcium chloride
6. Potassium sulphate
Which of the above salts may be dissolved in water to obtain hard water for the experiment?

  1. 1,3 and 5

  2. 1,2 and 5

  3. 1,2,4 and 6

  4. 3 and 5 only

  5. 2,3 and 5
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

The following salts may be dissolved in water to obtain hard water for the experiment
2. Calcium sulphate
3. Magnesium chloride
5. Calcium chloride

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

Both temporary and permanent hardness is removed on boiling water with :-

  1. $Ca(OH) _{2}$
  2. $Na _{2}CO _{3}$
  3. $CaCO _{3}$
  4. $CaO$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Temporary hardness is removed by boiling water with $NaOH$ and $Na _2CO _3$. $Ca(HCO _3 ) _2+2NaOH \rightarrow CaCO _3 \downarrow +Na _2CO _3+2H _2O$ Permanent hardness is removed by boiling water with sodium carbonate. $CaCl _2+Na _2CO _3 \rightarrow CaCO _3 \downarrow + 2 NaCl$

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.