Question

In how many grams of water should 25.31 g of potassium nitrate (kno3) be dissolved to prepare a 0.1982 m solution?

Answer 1

Answer: The mass of water that is needed to dissolve the given amount of potassium nitrate is 1263.1g

Step-by-step explanation:

To calculate the mass of solvent for given molality of solution, we use the equation:

`\text{Molality of solution}=\frac{m_(solute)* 1000}{M_(solute)* W_(solvent)\text{ (in grams)}}`

where,

Molality of the solution = 0.1982 m

`m_(solute)` = Given mass of solute
`(KNO_3)` = 25.31 g

`M_(solute)` = Molar mass of solute
`(KNO_3)` = 101.1 g/mol

`W_(solvent)`= Mass of solvent (water) = ?

Putting values in above equation, we get:

`0.1982=\frac{25.31* 1000}{101.1* \text{Mass of water}}\\\\\text{Mass of water}=(25.31* 1000)/(101.1* 0.1982)=1263.1g`

Hence, the mass of water that is needed to dissolve the given amount of potassium nitrate is 1263.1g

Answer 2

Molality:-It is a measure of the concentration of a solute in a solution in terms of amount of substance in a specified amount of mass of the solvent

Therefore,

Molality = moles solute / kg solvent

Therefore kg solvent = moles solute / molality

moles solute = mass / molar mass

= 25.31 g / 101.1 g/mole

= 0.2503 mole

kg solvent = 0.2503 mole / 0.1982 m

= 1.263 kg

= 1263 g

This is the required answer.