Chemistry

Chemical Compounds and Reactions

505 Questions

Chemical compounds and reactions involve understanding the properties, colors, and formation of various chemical substances. Questions focus on identifying precipitates, observing color changes during reactions, and naming common compounds. This topic is a fundamental part of the chemistry syllabus for competitive exams.

identifying precipitateschemical reaction colorscompound namingcolloidal particle propertiesacid base reactions

Chemical Compounds and Reactions Questions

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

Which of the following pair of ions makes the water hard?

  1. $Na^+,SO _4^{+2}$
  2. $Ca^{2+},HCO _3^-$
  3. $Ca^{2+},NO _3$
  4. $NH _4^-,Cr$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Causes

1) High mineral (calcium and magnesium) content.
2) It can be found in groundwater as it passes through lime.
Types 
1) Permanent: It is caused due to the presence of sulphate and chloride salts.  Heating does not remove the permanent hardness of water so it is treated with chemicals.  Resins or water softeners are used to remove the permanent hardness.
2) Temporary: It is caused due to the presence of bicarbonate salts.  It can easily be removed by boiling.  Boiling decomposes the salts into insoluble carbonates.  Water can also be treated with calcium hydroxide to remove the hardness.Water Hardeners are Ca2+ and HCO3.   Nitrates and sulfates are used as water softener.  

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

Calgon removes hardness by forming complex compounds with the $Ca^{2+}$and $Mg^{2+}$ ions of hard water or by adsorption.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Calgon is $(Na _6P _6O _{18})$ i.e. sodium hexa-metaphosphate. The calgon when added to hard water forms a  soluble complex.


$Na _2[Na _4(PO _3) _6]+2CaSO _4\longrightarrow 2Na _2SO _4+Na _2[Ca _2(PO _3) _6]$ soluble

In the same way, $Mg^{2+}$ can also precipitate as $Na _2[Mg _2(PO _3) _6]$ and water becomes free from $Mg^{2+}$ and $Ca^{2+}$ ions.

Thus the answer is True.

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

The formula of calgon is:

  1. $Na _{2}\left [ Na _{4}\left ( PO _{3} \right ) _{6} \right ]$
  2. $Na _{4}\left [ Na _{2}\left ( PO _{3} \right ) _{6} \right ]$
  3. $Na _{4}\left [ Na _{2}\left ( PO _{3} \right ) _{3} \right ]$
  4. $Na _{2}\left [ Na _{4}\left ( PO _{3} \right ) _{4} \right ]$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The formula of calgon is $Na _2[Na _4(PO _3) _6]$. Calgon is a trade name of a complex salt, sodium hexametaphosphate $(NaPO _3) _6$. It is used for softening hard water. 
Calgon ionizes to give a complex anion.
Multiple choice evs experiments with water water and its types hard and soft water what floats - what sinks
On treatment with cold water, an element (A) reacts readily liberating a colorless, odorless gas (B) and a solution (C). Lithium is reacted with (B) yielding a solid product (D) which effervescence with water to give a strongly basic solution (E). When $CO _2$ gas is bubbled through the solution (C), a white ppt (F) is formed but this redissolved forming solution (G) when more $CO _2$ is passed. The precipitate (F) effervesced when moistened with conc.$HCl$ and give deep red coloration to the Bunsen burner flame. (F) on heating with an excess of carbon at $2000^oC$ give (H).

Solution (G) contains a salt which:

(i) causes permanent hardness of water
(ii) can not be obtained in solid-state
(iii) causes temporary hardness of water
(iv) can be obtained in solid-state


Identify the salt with correct options.

  1. (i) and (ii)

  2. (i) and (iv)

  3. (ii) and (iii)

  4. (ii) and (iv)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The metal A is calcium. It reacts with cold water to form calcium hydroxide (C) and hydrogen gas (B) which is colourless and odourless.
$Ca+2H _2O \rightarrow Ca(OH) _2 + H _2$

Lithium reacts with hydrogen gas (B) to form a solid product LiH (D).
$2Li+H _2 \rightarrow 2LiH$

olid product LiH (D) effervescence with water to give a strongly basic solution (E). 
$LiH + H _2O \rightarrow LiOH+ H _2 $

When $CO _2$ gas is bubbled through calcium hydroxide solution (C) , a white ppt of calcium carbonate (F) is formed but this redissolved forming calcium bicarbonate (G) when more $CO _2$ is passed. 

$Ca(OH) _2 + CO _2 \rightarrow CaCO _3 \rightarrow+H _2O$

$CaCO _3+H _2O+CO _2 \rightarrow Ca(HCO _3) _2$

The precipitate (F) (calcium carbonate) effervesced when moistened with concentrated HCl and give deep red colouration to the Bunsen burner flame
$CaCO _3+2HCl \rightarrow CaCl _2 + H _2O +CO _2$

The deep red colour is the characteristic colour of calcium.
Calcium carbonate (F) on heating with excess of carbon at $2000^oC$ give calcium carbide (H).
$CaCO _3 + 3C \xrightarrow {2000^0C} CaC _2+CO+CO _2$

It is $CaHCO _3$ which cannot be obtained in solid-state and causes temporary hardness. Temporary hardness is due to the presence of calcium hydrogen carbonate.   

Hence Option-C is correct

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

In a permutit, the calcium and magnesium ions of hard water are exchanged by:

  1. $CO^{2-} _{3} $and $HCO _3{^-}$ ions of permutit
  2. $Na^{+}$ ions of permutit
  3. $Al^{3+}$ ions of permutit
  4. $Si^{4+}$ ions of permutiti
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Permutit is an artificial zeolite. It is sodium aluminium orthosilicate $Na _{2}Al _{2}Si _{2}O _{8}.xH _{2}O$.
$\underset {\text { permutit}}{Na _{2}Al _{2}Si _{2}O _{8}.xH _{2}O} + Ca^{2+}(or Mg^{2+}) \rightarrow  \underset {\text { exhausted permutit }}{Ca Al _{2}Si _{2}O _{8}.xH _{2}O} + 2Na^{+}$
Multiple choice chemistry metals physical properties of metals and non-metals some physical properties of metals general characteristics and uses of metals

Which of the following is the composition of red lead?

  1. $PbO$
  2. $PbO _2$
  3. $Pb _3O _4$
  4. $PbI _2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Lead($II,IV$) oxide also called minium, red lead or triplumbic tetroxide is a bright red or orange crystalline or amorphous pigment. It is used in the manufacture of batteries,lead glass and rust proof primer paints.

Multiple choice chemistry chemistry of non-metals physical properties of non-metals uses of metals and non metals physical properties of metals and non-metals

Silver jewellary turns black on long exposure to air. This is due to the formation of:

  1. $Ag _2O$
  2. $Ag _3N$
  3. $Ag _2O+Ag _3N$
  4. $Ag _2S$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Silver is stable in pure water and air but tarnishes when it is exposed to air or water containing hydrogen sulfide, the latter forming a black layer of silver sulfide which can be cleaned off with dilute $HCl$.

$2Ag+H _2S\rightarrow \underset {black.}{Ag _2S}+H _2$

Multiple choice chemistry nitrogen and sulfur ammonia-properties and uses ammonia compounds of nitrogen - ammonia

Ammonia is used in detection of $Cu^{2+}$ ion because:

  1. aqueous solution of $NH _{3}$ reacts with $Cu^{2+}$ ion to form deep blue coloured complex
  2. $NH _{3}$ reacts with $Cu^{2+}$ ion to give blue precipitate of $CuO$
  3. aqueous solution of $NH _{3}$ reacts with $Cu^{2+}$ ion to form white coloured complex.
  4. $NH _{3}$ reacts with $Cu^{2+}$ ion to give green precipitate.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Ammonia acts as a Lewis base due to the presence of lone pair of  on the nitrogen atom.so,it can form coordinate bond transition metal cations to from complex compounds.Ammonia reacts with a solution of $Cu^{2+}$  to from a deep blue coloured complex.The reaction for the above complex  compound can be written as follows:

$Cu^{2+}(aq) + 4 NH _3(aq)\rightarrow [Cu(NH _3) _4]^{2+}(aq)$

                                                                              Deep Blue

Hence option A is correct.

Multiple choice chemistry nitrogen and sulfur ammonia-properties and uses ammonia compounds of nitrogen - ammonia

Freshly prepared pure dilute solution of sodium in liquid ammonia :

  1. shows copper-bronze colour.
  2. occupy larger volume than that from the sum of the volumes of $Na$ and $NH _{3}(1)$.
  3. reduced the $GeH _{4}$ to $GeH _{2}^{-}$.

  4. produced sodium amide and hydrogen gas with rusty iron wire.
Reveal answer Fill a bubble to check yourself
A,D Correct answer
Explanation

In dilute solutions  of $Na$ in ammonia, the solvated electrons have a deep blue colour.

In more concentrated solutions, the solution takes on a bronze/copper colour.

The solution of sodium in liquid ammonia is quite stable on its own.

You need to add a small amount of a catalyst such as ${ FeCl } _{ 3 }$ for the sodium to react with the ammonia to form sodium amide and hydrogen gas.

$2N{ a } _{ (s) }+2N{ H } _{ 3(l) }\underrightarrow { \quad FeC{ l } _{ 3 } } 2NaN{ H } _{ 2 }(N{ H } _{ 3 })+{ H } _{ 2(g) }$
conclusion : hence the option (A) and(D) is correct.

Multiple choice chemistry nitrogen and sulfur ammonia-properties and uses ammonia compounds of nitrogen - ammonia

Sodium dissolved in ammonia has blue colour due to:

  1. solvated sodium molecule

  2. amide ion

  3. solvated electron

  4. lone pair of electrons on nitrogen in ammonia
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Ammonia solution turns blue when alkali and alkaline earth metals are dissolved in it. The blue color of the solution is considered to be due to ammoniated electrons which absorb energy corresponding to red region of the visible light for the their excitation to higher energy levels. The transmitted light is blue which imparts blue color to the solutions.

Multiple choice chemistry nitrogen and sulfur ammonia-properties and uses ammonia compounds of nitrogen - ammonia

Ammonia gas on passing through copper sulphate solution gives deep blue solution.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A blue precipitate of cupric hydroxide initially appears which on the addition of excess ammonia dissolves to form a deep blue solution having the tetraamminecopper(II) ion ${ \left[ Cu{ (N{ H } _{ 3 }) } _{ 4 } \right]  }^{ 2+ }$.

Multiple choice chemistry nitrogen and sulfur ammonia-properties and uses ammonia compounds of nitrogen - ammonia

Ammonia gas on passing through copper sulphate solution gives:

  1. yellow colour solution

  2. blue colour solution

  3. brown colour solution

  4. red colour solution
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Ammonia reacts with copper(II)ions to precipitate light blue copper hydroxide. Ammonia causes the copper ion to go back into the solution as a deep blue ammonia complex. The precipitate dissolves as we add an excess of ammonia.