How to find the mass of H when given mass of H2O?

Molar Mass of H2O= (1.008x2) + 16 = 18.016

hydrogen makes up 11.2% of H2O ----> (1.008x2) / 18.016

so 11.2% x 2.46 = .275g of Hydrogen

you need to use and learn dimensional analysis.. I cover it in my answer here

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one common unit factor you need to learn is mass fraction. mass H in mass H2O..

you know that 1 mole of H2O has mass = 2x1.008 + 1x16.00 = 18.02g

you know the mass of H in that H2O = 2x1.008 = 2.106g

so.. the rest is trivial

.. 2.46g H2O.. .. .2.016g H

---- ---- --- --- x ---- ----- ---- --- = 0.275g H

.. .. .. . .1.. .. .... 18.02g H2O

which you calculate by entering this in your calculator

.. 2.46 * 2.016 / 18.02 =

and rounding to 3 sig figs

(2.46 g H2O) / (18.01532 g H2O/mol) x (2 mol H / 1 mol H2O) x (1.007947 g H/mol) = 0.275 g H

Atomic weight of H is 1.008.

Molecular weight of H2O is 18.015.

Then 2.46 g of water contains this much hydrogen:

(2*1.008)*(2.46g)/(18.015) = around 0.27g but use a calculator

Mass of 1 mole of H₂O = (1.0×2 + 16.0) g = 18.0 g

Mass of H in 1 mole of H₂O = 1.0×2 g = 2.0 g

Mass fraction of H in H₂O = 2.0/18.0

Mass of H in 2.46 g H₂O = (2.46 g) × (2.0/18.0) = 0.273 g

0.28 mol x 1 g/mol = 0.28 g ⬅

for the oxygen 0.14 mol x 16 g/mol = 2.24 g

and they add up to 2.52, close but not close enough

You rounded too much, you have 3 digit values, so you need to carry 4 digits

water is 16+2•1.008 = 18.02 g/mol

2.46 g / 18.02 g/mol = 0.1365 mol

0.1365 mol x 2.016 = 0.275 g ⬅

for the oxygen: 0.1365 mol x 16 = 2.184 g

and they add to 2.459 g

close enough