Anyone know how to work this out???? (1 Viewer)

[poodoorfan]

Outline the procedure you would use to prepare a standard solution of sodium hydrogen carbonate from solid sodium hydrogen carbonate?

OR

Calculate the mass of solid sodium hydrogen carbonate required to make 250ml of 0.12molL-1 solution?

anyone know???? (For the first one) i know you gotta use like the RAMS and stuff but i have no idea how to work it out if they don't give you any measurements, like 5 grams of this or whatever, so does anyone know?

any help would be great cause i really get stuck on this stuff
thanks

 

[Dreamerish*~]

This might help - thanks to Andrew James.

For the first one, if they don't give you measurements, make it up - state clearly that you're making (for example) a ~0.01 M solution.

The steps are:

• Place solid sodium hydrogen carbonate in a dessicator or oven.
• After it has been dessicated, weigh out approximately 2 g (that's approximately 0.1 M, if you're using a 250 mL volumetric flask).
• Transfer sodium hydrogen carbonate from the watch glass to a clean 250 mL volumetric flash, use a wash bottle (with distilled water) to ensure complete transfer of solids.
• Add approximately 50 mL of distilled water to the volumetric flask and shake to dissolve all of the sodium hydrogen carbonate.
• Add distilled water until the bottom of the meniscus reaches the graduation mark on the volumetric flask.
• Cork the flask and shake.

I'm pretty sure that's it. I haven't studied any Chem since last term, but these things stick.

Calculate the mass of solid sodium hydrogen carbonate required to make 250ml of 0.12molL-1 solution?

0.12 mol L^-1 means 0.12 moles in one litre. As we're making a quarter of a litre, 0.12/4 = 0.03 moles is needed.

Molar mass of sodium hydrogen carbonate (NaHCO₃) is: 22.99 + 1.008 + 12.01 + 16 x 3 = 84.008 g.

0.03 moles is 0.03 x 84.008 = 2.52 g (2 d.p.)

Therefore 2.52 g of sodium hydrogen carbonate is required to make 250 mL of a 0.12 mol L^-1 solution.

 

[poodoorfan]

thank you so much, whe i read it i get it but when i have to work it out i just have no idea where to start.