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

Water samples (X and Y) from two different sources were brought to the laboratory for the measurement of dissolved oxygen (DO) using modified Winkler method. Samples were transferred to 300 ml BOD bottles. 2 ml of MnSO4 solution and 2 ml of alkaliodide-azide reagent were added to the bottles and mixed. Sample X developed a brown precipitate, whereas sample Y developed a white precipitate.

In reference to these observations, the correct statement is

  1. Both the samples were devoid of DO.

  2. Sample X was devoid of DO while sample Y contained DO.

  3. Sample X contained DO while sample Y was devoid of DO.

  4. Both the samples contained DO.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In the Winkler method, a brown precipitate (manganese hydroxide) indicates the presence of dissolved oxygen, while a white precipitate indicates the absence of dissolved oxygen.

Multiple choice chemistry d and f block elements imperfections in solids solid solutions formation of complex compounds and constituent of catalysts general characteristics of first transition series

Which of the following is not soluble in $NaOH$?

  1. $Fe(OH) _3$
  2. $Zn(OH) _2$
  3. $Al(OH) _3$
  4. $Sn(OH) _2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Fe(OH)3 is a basic hydroxide and does not dissolve in NaOH. Zn(OH)2, Al(OH)3, and Sn(OH)2 are amphoteric and dissolve in strong bases like NaOH to form soluble complexes.

Multiple choice chemistry the d-and f-block elements imperfections in solids solid solutions formation of complex compounds and constituent of catalysts general characteristics of first transition series
Find the solid which has brilliant blue color.
  1. $Fe _2O _3$
  2. $CuSO _4$
  3. $NaBr$
  4. $KCl$
  5. $Ca(OH) _2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Copper sulphate $\displaystyle CuSO _4$ has brilliant blue color.
$Cu(II)$ ions with an outer electronic configuration of  $\displaystyle 3d^{9}$ have one unpaired electron. This results in blue colour which is due to $d-d$ transitions.

Multiple choice

After reaction with potassium iodide and copper sulphate, sodium thiosulphate solution is added. Find the incorrect statement about this reaction.

  1. Cu2I2 is formed.

  2. CuI2 is formed.

  3. Na2S2O3 is oxidised.

  4. Evolved I2 is reduced.

  5. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When KI is added to the solution of cupper sulphate, an equivalent amount of I2 is liberated along with the formation white precipitate (of Cu2I2). This free iodine (I2), which remains in solution as [KI3] complex is then titrated with sodium thiosulphate solution using starch as indicator. At the end point of the titration, the blue colour of solution will disappear and a white precipitate of the Cu2I2 will remain in conical. The reactions that are taking place are: