Tag: chemistry

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

The law of traids is applicable to :

  1. $C, N, O$
  2. $H, O, N$
  3. $Na, K, Rb$
  4. $Cl, Br, I$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Dobereiner's triads work best for halogens like Cl, Br, I which show a clear pattern in properties and atomic weights. Groups like C, N, O or H, O, N don't form proper triads, and Na, K, Rb are alkali metals where the pattern doesn't hold well.

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

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

  1. electronic configuration

  2. properties

  3. number of shells

  4. both A and B
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $\text{B}$

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

The law of triads is not applicable to :

  1. $Os, Ir, Pt$
  2. $Ca, Sr, Ba$
  3. $Fe, Co, Ni$
  4. $Ru, Rh, Pt$
Reveal answer Fill a bubble to check yourself
C,D Correct answer
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 $\text{D}$

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

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

  1. $151$
  2. $75.5$
  3. $89.5$

  4. Unpredictable
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $

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

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:

  1. 24.5

  2. 49

  3. 34.5

  4. 29
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

Law of Triad was proposed by:

  1. Newland

  2. Gay Lussac

  3. Mendeleev

  4. Dobereiner
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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.

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $\text{A}$