Question

How come the balanced equation for calcium oxide reaction with water is: CaO (s) +H2O (l) --> Ca(OH)2 (s)?

Answer 1

CaO (s) +H2O (l) --> Ca(OH)2 (s)

# of moles of CaO and H2O
n = given mass / molar mass.
Ca = 40
O = 16
Mass CaO = 56 grams/mole

n = 2.50 / 56
grams/mole = 0.0446 moles

Molar mass = 2*H + O = 2 + 16 = 18 grams/ mol

n = 2.41 / 18 = 0.134 (WATER)

Now,
The number of moles of water left over.

moles of water - moles of water used in the reaction = left over moles.
0.134 - 0.0446 = 0.0893

The grams of water left over.

1 mole of water = 18 grams
0.0893 moles of water = X

X = 18 x 0.0893 = 1.61 grams of water not used in the reaction.

Answer 2

CaO(s) + H2O(l) ---> Ca(OH)2(aq)
CaO(s) + H2O(l) ---> 2CaOH(aq) we get this after balancing this equation
2CaO(s) + H2O(l) ---> 2CaOH(aq)
number of moles
CaO

n = given mass / molar mass.
Ca = 40
O = 16
Mass CaO = 56 grams/mole

n = 2.50 / 56 grams/mole = 0.0446 moles
Molar mass = 2*H + O = 2 + 16 = 18 grams/ mol
now in water
n = 2.41 / 18 = 0.134
moles of water - moles of water used in the reaction = left over moles.

0.134 - 0.0446 = 0.0893 remaining number of moles

grams of water which are left

1 mole of water = 18 grams
0.0893 moles of water = x

x = 18 * 0.0893 = 1.61 are grams of water used