We can calculate the mass percent of an element by dividing its atomic mass by the mass of the compound and then multiply by 100:
% by mass of element = (mass of element/mass of compound) x100%
Impurities like n-eicosane with the molecular formula C20H42 could account for the low percent by mass of oxygen in the sample because it has a zero percent oxygen based on its compound formula which indicates that it does not have the element oxygen.
Answer : The correct option is, Only Student B
Explanation :
Lewis-dot structure : It shows the bonding between the atoms of a molecule and it also shows the unpaired electrons present in the molecule.
In the Lewis-dot structure the valance electrons are shown by 'dot'.
The given molecule is, 
As we know that nitrogen has '5' valence electrons and hydrogen has '1' valence electron.
Therefore, the total number of valence electrons in = 5 + 3(1) = 8
According to Lewis-dot structure, there are 6 number of bonding electrons and 2 number of non-bonding electrons.
The Lewis dot structure of student A is wrong because there is a coordinate bond present between the nitrogen and hydrogen is not covalent.
Thus, the correct Lewis-dot structure of is shown by the student B.
Molality is the number of moles of solute in 1 kg of solvent
number of moles of sucrose - mass of sucrose / molar mass
number of moles of sucrose - 34.2 g / 342.34 g/mol = 0.0999 mol
number of moles in 125 g of water - 0.0999 mol
therefore number of moles in 1000 g - 0.0999 / 125 x 1000 = 0.799 mol/kg
molality of sucrose solution - 0.799 mol/kg
to the proper number of significant figures) to the following? (12.67+19.2)(3.99)/(1.36+ 11.366).
B ase from the reaction <span>cacn2 3 h2o → caco3 2 nh3, for every 1 mole of caco3 produced there 2 moles of nh3 being produced. to solved this, we must first convert the caco3 to moles.
mass nh3 = 187 g caco3 (1 mol caco3 / 100 g caco3 ) ( 2 mol nh3 / 1 mol caco3) ( 17 g nh3 / 1 mol nh3)
mass nh3 = 63.58 g nh3 is produced</span>
