How many moles of NH3 are there in  250cm³ of a 30% solution , the specific gravity of which is 0.90?

Dear student
Please find the solution to the asked query:

Given -
volume of water = 250 mL
density of solution = 0.9 g/mL
Calculation -
Since ammonia dissolved in water is 30% by weight, then using mass % formula, we can calculate the amount of ammonia in water.
mass %  = mass of ammonia/ mass of solution×100 
30 = mass of ammonia/ mass of ammonia + mass of water×100 
At 4^oC, density of water  = 0.999 g/mL
since density = mass /volume
0.999  = mass/ 250 
mass of water = 249.75 g
​now, let mass of ammonia be x.
$$\begin{gathered} \frac{30}{100}=\frac{x}{x+249.75} \\ 30x +7492.5 = 100x \\ 70x = 7492.5 \\ x=107.03g \end{gathered}$$

Thus, ammonia dissolved in 250mL water is 107.03 g

Moles of ammonia = mass of ammonia/molar mass
                             = 107.03g/17gmol^-1
​                                =6.3 moles

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