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/sci/ - Science & Math

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2463949 No.2463949 [Reply] [Original]

I have a chemistry question: If the reagent in an experiment is NaOH(s), the mass dissolved is 1.74(g), the solution volume is 0.500(L) and the entity is OH-(aq), what would the concentration(mol/L) be? I am just starting my grade 12 chem and I am fucking blanking on how to solve this problem. I'm pretty sure I need to make a formula where I put 0.500 like: 1/0.500 so I can have litres on the bottom because it is mol/L. How do I chem?

>> No.2463958

just whisk in the eggs at the end for fluffier waffles

>> No.2463971

>>2463958
I agree adding lime like OP is implying would make it taste terrible.

>> No.2463985

>>2463971
OP here, should I add more flour to make the dough less flakey of just tell you guys to shut the fuck up?

>> No.2463999

bump

>> No.2464018

ill help...
i mol NaOH = Na (11) + O (8) + H (1) = 19g/mol
(19g/mol) / 1.74g = 0.020mol NaOH
.020mol/.5litres = 0.04mol/l

>> No.2464025

>>2464018
too bad that answer is wrong

>> No.2464034

>>2463971 lime

never had pretzels? (oh shit I said waffles. my bad)

>> No.2464036

why so?>>2464025

>i mol NaOH = Na (11) + O (8) + H (1) = 19g/mol
so Oxygen is only 8 because it's polyatomic and since it's only using the mol, it's 8 instead of 16?

>> No.2464042

>>2464018
>>2464036
>atomic numbers
trolololol

>> No.2464046

>>2464025
help me man, just tell me HOW then i'll see if i can solve it!!

>> No.2464067

btw, molar wright is the weight of 6.02214078×10 to the 23rd power molecules of a substance... molar weight is just the weight of all constituents in a substance... when working with chemistry problems treat it as a variable when writing (like 15x just replace 'x' with 'g/mol' like 15g/mol) and work thru problems treating it as such... so O2 is 2 oxygens each with an atomic mass of 8... so the molar weight of O2 is 16g/mol...

>> No.2464073

>>2464025
is the answer 0.02175?

>> No.2464083

>>2464046

>>2464036
There is no oxygen gas in this equation so the fact it is diatomic (as a gas) is irrelevant. Also you always use the atomic mass, not the atomic number. Finally although this ends up being being irrelevant in the end (thanks to 1 Na to 1 OH ratio) NaOH is the reagent, the answer we are looking for is the concentration of OH-.

>> No.2464095

>>2464083
i know i am looking for the concecntration of OH- but i have no idea of what kind of formulas or shit is needed.

>> No.2464099

>>2464067
This guy is a fucking idiot, don't listen to him.

>> No.2464105

>>2464095
molar mass = g/mol

>> No.2464115

>>2464105
the molar mass of NaOH is 40g/mol, right?
then do I divide (1.74*0.5) by 40 to get 0.02175?

>> No.2464117

c_OH = n_OH/V
n_NaOH = n_OH = m_NaOH/M_NaOH
=> c_OH = m_NaOH/(M_NaOH * V)
M_NaOH = M_O + M_Na + M_H = 40 g/mol
V = 0.5 l
=> c_OH = 1.74 g / (40 g/mol * 0.5 l) = 0.087 mol/l

>> No.2464126

>>2464117
This is right though difficult to read

>> No.2464132

>>2464115
when you divide by 40 g/mol so mol ends up on top

>> No.2464136

>>2464115
when you divide by 40 grams per mole so you get mols on top, you then divide by the volume in liters, not multiply to get the concentration

>> No.2464149

>>2464117
>>2464136
so essentially: concentration=n(?)/volume; n=mass/Molarmass?

>> No.2464169

>>2464149
exactly. where n= number of mols

>> No.2464185

>>2464169 where n= number of mols

I read that as n = number of trolls. Time to get off 4ch for the day.

>> No.2464211

OP, you see, units are everything you need.
In this example you have a mass (g) and a volume (l) and want to know a molar concentration (mol/l), so you'll need the amount of substance (mol) that corresponds to your mass. But how the fuck do you get from g to mol?

For that, you just need to look up and add the molar masses of the atoms in your molecule (g/mol).

Now think for a second - when you've got g/mol and g, what could you do to get mol? You just divide g / (g/mol), i.e. 1.74 / 40, and you're set.

All that's left to do is to divide mol with liters and you'll get mol/l. Fucking magic.

>> No.2464227

That's the concentration of Tiger in that tub?

>> No.2464256
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2464256

>>2464169
>>2464211
it makes sense now, thanks guys.