Chemistry Forum

This topic is about molality

How many grams of NaHCO₃ are needed to prepare a 2 molar solution with 200 mL of water?

Can someone help me, Thanks.!!!

Do you want molality or molarity. Both are different.

Molarity is concentration in mass/volume like g/l. Molality is mass/(mass of solution). Like g/kg.

For molarity you need molar mass of NaHCO₃ what is 84 g/mol.

A 2 M solution contain 2 mol/l. So you have to dissolve 168 g and fill up with water to 1 l, for 200 ml you need 33,6 g.

For a 2 molal solution you take a balance put in a beaker glass 168 g NaHCO₃ and add water to 1 kg , what should be 832 g H₂O. For 200 g you need 33,6 g NaHCO₃ and 166,4 g H₂O.

But both is not possible, because solubility is max. 93,4 g/l what means 1,11 mol

its about molality, thanks for answer, is a question for my class, but I don't understand, because I resolve it, and tha answer was 252 g, buy I'm not sure

252 g is definitive wrong. How do you calculate.

Yes, you right,

I solved it again and I used this method:

molality Solute = m(molality) * molar weight * Kg

mste: 3 * 84 * 0.2 ( 200 ml to kilogram) = 50.4

i think, that this is the answer

No, the answer I had given above 33,6 g NaHCO₃ and 166,4 g H₂O to make 200g, not 200 ml.For calculation you need also specific gravity of the solution.
200 ml is not 200 g.

3 * 84 * 0.2 ( 200 ml to kilogram) = 50.4

Where does the 3 comes from ? Check also the unit.

3? * 84 / g/mol * 0,2 l = 50,4 ?* g/mol * l



The unit must be g/kg