Question

1-calculate the mass of 4 moles of Na

Answer 1

1. 92 g

2. 5.4 g

3. 0.217 moles

Further explanation  

The mole is the number of particles(molecules, atoms, ions) contained in a substance  

1 mol = 6.02.10²³ particles

Can be formulated

N=n x No

N = number of particles

n = mol

No = Avogadro's = 6.02.10²³

Moles can also be determined from the amount of substance mass and its molar mass

$\tt n=\dfrac{m}{MW}$

1. the mass of 4 moles of Na(MW= 23 g/mol)

$\tt mass=mol\times MW\\\\mass=4\times 23\\\\mass=92~g$

2.  the mass of 0.3 moles of water(MW=18 g/mol)

$\tt mass=mol\times MW\\\\mass=0.3\times 18\\\\mass=5.4~g$

3. the number of moles found in 10g of ethanol C2H5OH(MW=46 g/mol) :

$\tt mol=\dfrac{10}{46}\\\\mol=0.217$