Question

Calculate the number of particles in a 0.75 gram sample of Calcium Nitrate; Ca(NO3)2​

Answer 1

The number of particles : 2.75 x 10²¹

Further explanation  

A mole is a unit of many particles (atoms, molecules, ions) where 1 mole is the number of particles contained in a substance that is the same amount as many atoms in 12 gr C-12  

1 mole = 6.02.10²³ particles  

$\tt n=\dfrac{N}{N_o}$

N = number of particles  

No = Avogadro number (6.02.10²³)  

n = number of moles  

While the number of moles can also be obtained by dividing the mass (in grams) with the molar mass of element or molecule  

0.75 gram sample of Calcium Nitrate; Ca(NO₃)₂

MW of Ca(NO₃)₂ : 164.09 g/mol

$\tt mol~Ca(NO_3)_2=\dfrac{0.75}{164.09}=0.00457$

The number of particles

$\tt N=n\times N_o\\\\N=0.00457\times 6.02\times 10^{23}=2.75\times 10^{21}$