Tag: chemistry

Questions Related to chemistry

The law of triads was given by :

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

  1. Dobereiner

  2. Lewis

  3. Mendeleev

  4. Dalton

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Correct Option: A
Explanation:

In the year 1829, Johann Wolfgang Dobereiner, a German scientist, was the first to classify elements into groups based on John Dalton's assertions. He grouped the elements with similar chemical properties into clusters of three called 'Triads'. The distinctive feature of a triad was the atomic mass of the middle element. When elements were arranged in order of their increasing atomic mass, the atomic mass of the middle element was approximately the arithmetic mean of the other two elements of the triad.

If the two members of a Dobereiner's triad are chlorine and iodine, then the third member of this triad is :

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

  1. fluorine

  2. bromine

  3. sodium

  4. calcium

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Correct Option: B
Explanation:

According to Dobereiner, the atomic mass of the middle element is nearly equal to the arithmetic mean of the other two. Therefore, the atomic mass of the third element is $=$ $\dfrac{{35.5}+{127}}{2}$ $=$ 81.25, which is the atomic mass of bromine.

If the two members of a Dobereiner triad are phosphorus and antimony, the third member of this triad is :

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

  1. arsenic

  2. sulphur

  3. iodine

  4. calcium

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Correct Option: A
Explanation:

According to Dobereiner, the atomic mass of the middle element was nearly equal to the arithmetic mean of the other two. Therefore, the atomic mass of the third element is $=$ $\frac{{31}+{121.75}}{2}$ $=$ 76.37 which is nearly equal to the atomic mass of arsenic.

Cl, Br, I  follows Dobereiner's triads, the atomic masses of Cl and I are 35.5 and 127 respectively. The atomic mass of Br is : 

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

  1. 162.5

  2. 91.5

  3. 81.25

  4. 45.625

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Correct Option: C
Explanation:

According to Dobereneir's triads the atomic mass of Br will be average of the atomic masses of CI & I
 $=$ $\frac{{35.5}+{127}}{2}$ $=$ 81.25

Which of the following sets of atomic masses do not correspond to Dobereiner's triad?

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

  1. 7, 23, 39

  2. 20, 38, 56

  3. 47, 91, 178

  4. 54, 95, 183

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Correct Option: C,D
Explanation:

The atomic mass of the middle element should be the average of the atomic masses of the first and third elements. In case of C and D options, the atomic masses do not correspond to that rule.

Which of the following triads does not follow Dobereiner's law of triads?

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

  1. Li, Na, K

  2. Ca, Sr, Ba

  3. Be, Mg, Ca

  4. Cu, Ag, Au

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Correct Option: D
Explanation:

Since the atomic weight of Ag is not equal to the mean of the atomic weights of Cu and Au.


Thus, (Cu, Ag, Au) triad do not follow Dobereiner's law of triads.

Option D is correct.

Which of the following set of elements cannot be a triad?

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

  1. $Li, Na, K$

  2. $B, Al, Ga$

  3. $Be, Mg, Ca$

  4. $Cl, Br, I$

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Correct Option: B
Explanation:

Triad can be only when the middle element is having mean atomic weight of other two elements $,$ which $B, Al, Ga$ does not have such triad$.$

Which of the following elements follow Dobereiner's law of Triads?

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

  1. Na = $23$, Li = $7$ and K = $39$

  2. Cl = $35$, Br = $80$ and F = $19$

  3. Ca = $40$, Mg = $24$ and Sr = $88$

  4. Na = $23$, K = $39$ and Rb = $85$

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Correct Option: A
Explanation:

According to Dobereiner's, the atomic weight of the middle element is nearly the same as the average of the atomic weights of the other two elements.


$Li(7)+K(39)\longrightarrow \cfrac{7+39}{2}=Na(23)$

So, $Na=23, Li=7$ and $K=39$ 

The correct option is ( A ) 

Following triads have approximately equal size

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

  1. ${ Na }^{ + },\quad { Mg }^{ 2+ },\quad { Al }^{ 3+ }$

  2. ${ F }^{ - },\quad Ne,\quad { O }^{ 2- }$

  3. $Fe,\quad Co,\quad Ni$

  4. ${ Mn }^{ + },\quad { Fe }^{ 2+ },\quad Cr$

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Correct Option: C

The law of  traids is not applicable on

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

  1. $Cl, Br,I$

  2. $Na, K, Rb$

  3. $S, Se, Te$

  4. $Ca, Sr, Ba$

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Correct Option: B