The number of molecules in the substance MgNO2, the mass of which is 210 g.

Given:
m (Mg (NO2) 2) = 210 g
NA = 6.02 * 10 ^ 23 mol − 1

To find:
N (Mg (NO2) 2 molecules) -?

Solution:
1) Calculate the molar mass of Mg (NO2) 2:
M (Mg (NO2) 2) = Mr (Mg (NO2) 2) = Ar (Mg) * N (Mg) + Ar (N) * N (N) + Ar (O) * N (O) = 24 * 1 + 14 * 2 + 16 * 2 * 2 = 116 g / mol;
2) Calculate the amount of Mg (NO2) 2:
n (Mg (NO2) 2) = m (Mg (NO2) 2) / M (Mg (NO2) 2) = 210/116 = 1.81 mol;
3) Calculate the number of Mg (NO2) 2 molecules:
N (Mg (NO2) 2 molecules) = n (Mg (NO2) 2) * NA = 1.81 * 6.02 * 10 ^ 23 = 10.9 * 10 ^ 23 = 1.09 * 10 ^ 24.

Answer: The number of Mg (NO2) 2 molecules is 1.09 * 10 ^ 24.



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