Answer:
0.625 M
Step-by-step explanation:
Data Given:
mass of NaOH = 20 g
Weight of water = 800 g
As 1 kg of water = 1 kg of water
So we can write Kg instead of Liter
So convert grams to to Kilograms
1 g = 0.001 g
So
800 g = 800 /1000 = 0.8 kg
Solution:
As molarity is related to concentration of the solution
So the formula to calculate molarity is as under
Molarity = moles of solute / Kg of solution . . . . . . . . (1)
So first we have to find moles of 20 g NaOH
For mole we use formula
no. of moles = mass in g/ molar mass .. . . . . . . (2)
Molar mass of NaOH = 23 + 16 + 1
Molar mass of NaOH = 40 g /mole
put values in equation 2
no. of moles = 20 g / 40 g
no. of moles = 0.5 mole
Now we have to dissolve 0.5 NaOH in 0.8 kg of solution, now to make this composition in 1 kg of solution
Now put the values in equation 1
Molarity = moles of solute / Kg of solution
Molarity = 0.5 moles / 0.8 kg x 1 kg
Molarity = 0.625 M
Molarity of 20 g NaOH = 0.625 M