Tag: chemistry

Questions Related to chemistry

The law of traids is applicable to :

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. $C, N, O$

  2. $H, O, N$

  3. $Na, K, Rb$

  4. $Cl, Br, I$

Show answer
Correct Option: D

In the Doberiener's triad, all three elements have similar:

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. electronic configuration

  2. properties

  3. number of shells

  4. both A and B

Show answer
Correct Option: B
Explanation:

In the Doberiener's triad, all three elements have similar properties and the atomic weight of the middle member of each triad is very close to the arithmetic mean (average) of the other two elements.


The Dobereiner's triads include (1) Li, Na, K (2) Ca, Sr, Ba and (3) Cl, Br, I.

Hence, the correct option is $\text{B}$

The law of triads is not applicable to :

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. $Os, Ir, Pt$

  2. $Ca, Sr, Ba$

  3. $Fe, Co, Ni$

  4. $Ru, Rh, Pt$

Show answer
Correct Option: C,D
Explanation:

The law of triads does not apply to $Ru, Rh, Pt$.


According to the law of triads, the atomic weight of the middle element is approximately equal to the arithmetic mean of the other two elements.

The atomic weights of $Ru, Rh$ and $Pt$ are $101, 102.9$ and $195$ respectively.

The arithmetic mean of the atomic weights of $Ru$ and $Pt$ is $\displaystyle \dfrac {101+195}{2} = 148$
Hence, the atomic weight of $Rh$ is not equal to the arithmetic mean of the atomic weights of $Ru$ and $Pt$.

$Fe = 56, Co = 59$ and $Ni = 59$

Mean of the weights of $Fe$ and $N$i is not equal to the weight of $Co$.


Hence, the correct options are $\text{C}$ and $\text{D}$

Atomic wt. of P is 31 and Sb is 120. What will be the atomic wt. of As, as per Dobernier triad rule?

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. $151$

  2. $75.5$

  3. $89.5$

  4. Unpredictable

Show answer
Correct Option: B
Explanation:

Atomic wt. of P is 31 and Sb is 120. The atomic wt. of As, as per Dobernier triad rule will be average of two. It will be $\displaystyle \frac {31+120}{2} = \frac {151}{2} =75.5 $

Atomic wt. of $Cl = 35.5$ and of $I = 127$. According to Doeberiner triad rule atomic wt. of $Br$ will be:

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. $80.0$

  2. $162.5$

  3. $81.25$

  4. $91.5$

Show answer
Correct Option: C
Explanation:

Atomic wt. of Cl = 35.5 and I = 127.


According to Doberiner triad rule:

Br =$\dfrac {35.5 +127}{2}=\dfrac {162.5}{2}=81.25$

Hence, the correct option is $\text{C}$

If three elements X, Y, and Z form a Dobereiner's triad and atomic weights of X and Z are 9 and 40 respectively, then the atomic weight of the element Y is approximately:

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. 24.5

  2. 49

  3. 34.5

  4. 29

Show answer
Correct Option: A
Explanation:

According to Dobereiner, the atomic weight of the central element of the triad is the arithmetic mean of the atomic weights of the other two members. 


Therefore, atomic weight of Y = $\cfrac{9 + 40}{2} = 24.5\ g$


Hence, option A is correct.

Law of Triad was proposed by:

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. Newland

  2. Gay Lussac

  3. Mendeleev

  4. Dobereiner

Show answer
Correct Option: D
Explanation:

Dobereiner, in 1817 suggested a relationship between the properties of elements and their atomic weights. According to Dobereiner, the atomic weight of the middle element is nearly the same as average of the atomic weights of other two elements.

The element in between lithium and potassium in Dobereiner's classification is:

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. Mg

  2. Na

  3. Ca

  4. Rb

Show answer
Correct Option: B
Explanation:

Li, Na, K formed a Dobereiner's triad. Thus the element between Lithium and potassium is Sodium (Na).

Chlorine, Y and Iodine form a Dobereiner's triad. Identify the atomic weight of Y.

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. 162.5

  2. 81.25

  3. 121.5

  4. 90.5

Show answer
Correct Option: B
Explanation:
Cl, Y and I for Dobereiner's triad. Thus weight of Y is arrange of weight of Cl and I
$\therefore$ Atomic weight of Y is $\cfrac { 35.5+127 }{ 2 } =81.25$

Three elements X, Y and Z form a Dobereiner triad. The ratio of the atomic weight of X to that of Z is 7: 25.


 If the sum of the atomic weights of X and Z is 160, find the atomic weights of X, Y and Z.

chemistry the periodic table dobereiner's triads development of the modern periodic table into the history

  1. X $\rightarrow$ 35, Y $\rightarrow$ 80, Z $\rightarrow$ 125

  2. X $\rightarrow$ 125, Y $\rightarrow$ 80, Z $\rightarrow$ 35

  3. X $\rightarrow$ 80, Y $\rightarrow$ 35, Z $\rightarrow$ 125

  4. X $\rightarrow$ 80, Y $\rightarrow$ 125, Z $\rightarrow$ 35

Show answer
Correct Option: A
Explanation:
Let weight of X be $7a$  $\therefore$ Atomic weight of $Z=25a$

$\therefore7a+25a=160$

$\Rightarrow a=5$

Weight of X$=35$ and of Z is $125$

Atomic weight of Y is arranged of X and $2=\cfrac { 35+125 }{ 2 } =80$

Hence, the correct option is $\text{A}$