Asample of a hydrated compound has a mass of 5.1 g. during heating, it loses 1.1 g, leaving 4.0 g. what is the percentage by mass of water in the original hydrate?

6.11%
21.6%
27.5%
78.4%

21.6%

Explanation: From given information, mass of hydrate is 5.1 g. It loses water on heating. So, mass of water in the hydrate is 1.1 g.

(4.0 g is the mass of the unhydrated salt which is not of our use to solve this problem.)

Percent by mass of water in the original hydrate is the mass of water divided by the mass of hydrate and multiplied by 100.

water percentage in hydrate =

water percentage in hydrate =

water percentage in hydrate = 21.6%

So, choice C) 21.6% is correct.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."