Calculate the molecular weight of a substance. in which the solution of this substance in the water has a concentration of 7 percent by weight, has a freezing point
equal to -0.89 ° c, set kf value of water = 1.86 ° c / m

Answer : The molecular weight of a substance is 157.3 g/mol

Explanation :

As we are given that 7 % by weight that means 7 grams of solute present in 100 grams of solution.

Mass of solute = 7 g

Mass of solution = 100 g

Mass of solvent = 100 - 7 = 93 g

Formula used :  

where,

= change in freezing point

= temperature of pure water =

= temperature of solution =

= freezing point constant of water =

m = molality

Now put all the given values in this formula, we get

Therefore, the molecular weight of a substance is 157.3 g/mol

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles