Question

Approximate atomic weight of an element is $26.89g$. If its equivalent weight is $8.9g$, the exact atomic weight of the element would be:
A.$29.8$
B.$8.9$
C.$17.8$
D.$26.7$

Answer 1

Hint: Equivalent weight is the quantity of substance that reacts with a fixed quantity of another substance. The equivalent weight of an element is the gram atomic weight divided by its valence.

Complete step by step answer:
We know, ${\text{Equivalent weight}} $= $\dfrac {{{\text{atomic weight}}}} {{{{valency}}}} $
To take out exact atomic weight, we need to find valency. The formula for valency is
${{Valency =}}\dfrac {{{\text{equivalent weight}}}} {{{{atomic weight}}}} $
Putting the values in the formula,
${{Valency =}}\dfrac{{26.89}}{{8.9}}$
We get,$26.7$$ = 2.99$
Now to find out the exact atomic weight we have to put the values in the formula and get the answer.
${\text{Exact atomic weight = Equivalent weight}} \times {{valency}} $
=$8.9 \times 2.99$
We get,$
   = 26.6 \\
    \\
 $
Now we know that exact atomic weight is $26.6$, looking at the options we will choose the value closest to this number.
Then the correct option will be (D) $26.7$.

ADDITIONAL INFORMATION:
Approximate atomic weight is calculated when, you know the number of protons and neutrons for a particular isotope.
Equivalent weight is known as the mass of one equivalent or the mass of a given substance which combines or displaces a fixed quantity of another substance. The atomic weight of any elements is also called relative atomic mass atomic weight is measured in an atomic mass unit also known as Daltons.

Note:Atomic weight or atomic mass of an element is the mass of an atom, its SI unit is\[Kg\] or kilogram. It can often be expressed in Dalton as well. Protons and neutrons inside the nucleus of an atom comprises its atomic mass as a whole.