Question

Calculate the number of atoms of each type in 5.3g of Na2 Co3 (at.mass of Na=23,C=12 & O =16)

Answer 1

Mass of Na2CO3 is given as 5.3g
1st step : we calculate the molar mass of Na2CO3 by using the atomic masses gvien to us (Na =23, C =12, O =16 ) = 2x23 + 1x12 + 3x16 = 106g/mol
2nd step : we convert the given mass 5.3g of Na2CO3 to moles of Na2CO3 using the formula ==> moles = mass given / molar mass ( calculated in 1st step)
moles = 5.3g /106g/mol
= 0.05 moles
3rd step : we convert the moles to molecules using the Avogadro's number 6.023 x 10^23 , formula to be used ===> Number of molecules = moles x Avogadro's number
=0.05 moles x 6.023 x 10^23 molecules / mole
=0.30115 x 10^23 molecules
= 3.0115 x 10^22 molecules

4th step : now look at the formula Na2CO3 ,as per this formula each molecule of Na2CO3 contains 2 Na atoms , 1C atom and 3 O atoms
therefore no of Na atoms = no of molecules x no of atoms per molecule
= 3.0115 x 10^22 molecules of Na2CO3 x 2 atoms of Na / 1molecule of Na2CO3
=6.023 x 10^22 atoms of Na

therefore no of C atoms = no of molecules x no of atoms per molecule
= 3.0115 x 10^22 molecules of Na2CO3 x 1 atom of C / 1molecule of Na2CO3
=3.0115 x 10^22 atoms of C

therefore no of O atoms = no of molecules x no of atoms per molecule
= 3.0115 x 10^22 molecules of Na2CO3 x 3 atoms of O / 1molecule of Na2CO3
= 9.0345 x 10^22 atoms of O