Need help

[Labbie]

Sorry folks, but I am so busy, and only me again.

I need 250ml of 0.5% Sodium hydrogen Carbonate (Sodium Bicarbonate)
& 250ml 0.4% of HCL

Odd request, and I just can not think.

Help

[sunray18]

I maybe as brain dead this morning as you are;
but
for the sodium bicarbonate - 0.5gm in 100 mls water would be a 0.5% solution
and 0.4mLs of conc HCl in 100 mLs would be a 4% as far as we in schools need it..
If I were asked for it, I wouldnt bother about thinking about molarity - just a straight dilution

NOW to await brighter minds to sya if this is so...

[dime]

This is how I would do it. For the sodium bicarbonate you will need 2.5g and 250ml water
For the Hcl 1ml and 249ml water. Not sure that this is correct, as we usually work in molarity don't we. But it is what I would do, and they probably won't know any differently.

[RosalieM]

Conc HCL is usually (I think!) 94-98% so I reckon you'd be pretty safe with the 0.4ml/100ml but since you want 250ml you need to do 0.4x2.5 = 1ml so if you have a 1ml pipette I'd be using that and then use a 250ml volumetric flask to make it up. It should be accurate enough for high school science, even if it is a senior class.

Also for the sodium bicarbonate just do what sunray18 said as well. 0.5g/100ml so do 0.5x2.5 = 1.25g for 250ml. Again, I would make it up in a volumetric flask since they are such low concentrations.

Happy mixing!

[dime]

Ooops, got fuzz brain too. It should have read 1.25 g of sodium bicarbonate. sorry

[Labbie]

Thank you all so much, you are the best

[RosalieM]

Don't worry Labbie - I'm sure all of us have days when our brains just refuse to switch on! I had a Geography teacher email me the other day asking if we have any hygrometers (and a few other things) she could borrow for a year 7 class. I emailed back saying we don't have hygrometers but we have wet/dry bulb thermometers for humidity! Silly me... the wet/dry bulb thermometers ARE hygrometers!! I really don't know what I was thinking... obviously I wasn't thinking much at all!

[nickykinz]

Sorry to confuse matters but.......
Our Conc HCl is either 32 or 36% making it ~10-12 M. According to Chemwatch 0.1M is 0.37% so would probably be close enough. I often use chemwatch for percentages as the mini MSDS usually says at the top what the percentages are and then you can often work out where you need to be.

[Labbie]

Thanks Rosalie that helps me feel a little better.

[RosalieM]

True. As soon as I read nickykinz's post above I thought "Oh yeah, that sounds right. I bet it's H2SO4 that I'm thinking of." That's the problem of not having a computer near where the chemicals are. It's too much of a hike to go check!! Thanks for the clarification and for picking up on my error - There you go labbie! I'll make you feel even better again!!!

[DavidPeterson]

Conc HCL is usually (I think!) 94-98%

I think you are confusing HCl with conc H2SO4, which is normally about 98%.

HCl is actually a gas, so 94-98% would still be a "moist" gas! The conc HCl I get is 32%

[mtg]

Now I'm confused. If the conc HCl is around 32-33% would you then multiply the HCl amount by 3?, as the calculations are based on concentrated being 100%. But then you still have 67-68% of it as a liquid I'm assuming water. I dont even need it but I remember being totally flummoxed by this dilemma in the past.