How many water molecules in a #0.90*g# mass of water?

3 Answers
Oct 25, 2017

Answer:

#3.01xx10^22# molecules.

Explanation:

The mass of one mole of water is #"18 g"#. Therefore, #"0.9 g"# of water is

#"0.9 g"/"18 g/mol" = "0.05 moles"#

of water. One mole of water contains Avagadro's constant, ie, #6.022 xx 10^23# molecules of water, therefore, #0.05# moles of water contain

#"0.05 mol" xx (6.022^23"molec.")/("1 mol") = 3.01xx10^22# #"molecules"#

Oct 25, 2017

Answer:

We find the molar quantity.....and get #"number of water molecules"# #=3.01xx10^22#...

Explanation:

#"Moles of water"=(0.9*g)/(18.01*g*mol^-1)=0.050*mol#

And we know that there are #6.022xx10^23# molecules in one mole of any substance.....

And so we take the product......

#0.050*molxx6.022xx10^23*mol^-1=3.01xx10^22# #"water molecules"#. (And thus the product gives a dimensionless number as required....)

(i) how many oxygen atoms in this molar quantity; and (ii) how many hydrogen atoms......?

Oct 25, 2017

Answer:

#30.1# x #10^21 mlcs#

Explanation:

#Mass of water(H_2O)# #= 0.9grams#

#Molar mass of (H_2O)# #= 1.008# x # 2# + 1#6#
# = 18.016gmol^-#

Number of molecules = Mass in grams#/#Molar mass x #N_A#

#= 0.9/18.016# x #6.02# x #10^23#

# = 30.1# x #10^21 # #mlcs #