Bazza's 3/4 chemistry questions

[WhoTookMyUsername]

1) what is a good dictionary for chemistry ( equivalent of hendersons for biology ) ?
2) is "heating to constant mass" generally done at 100C or 110c ?

Thanks

[Lasercookie]

2) is "heating to constant mass" generally done at 100C or 110c ?

I think if you're trying to get rid of water (e.g. in order to determine the percentage of water in a substance by comparing the mass before and after), you do it at higher than 100 degrees (e.g. 110 degrees). By doing this, you can better ensure that all of the water will vaporise.

This would mean a more accurate calculation in the end, as you can be more positive that all the water and stuff has been removed from the substance.

I can't remember exactly what the prac was, but we did something similar to this in Unit 2 for stoich (I think it was that topic), where we heated the substance at a slightly higher temperature than it's boiling point (something like that) for that reason above.

[paulsterio]

If you heat water at 100 degrees C, it won't evaporate because of latent heat, it was in unit 1, i think, so heating to constant mass has to be at a temperature above 100

btw, i like your subjects laseredd, it's mine + ITA

[REBORN]

latent heat is u2. it's 110 deg C to ensure all water is gone.

[pi]

1) what is a good dictionary for chemistry ( equivalent of hendersons for biology ) ?

You don't need one. Google is the best if you ever do though.

[HERculina]

just wondering, is relative molecular mass the same as relative molar mass?
do we need to remember anything about s,p,d shells, electron configuration, gas laws? or is it just unit 2 redox, stoich and acids and bases
PS. sorry Bazza i ceebs making my own thread

[Ravit]

gas laws yes ! not sure about the shells, i would just know them for general knowledge and overall understanding of chemistry as a whole.
And could someone also the answer the question upon reletive molecular mass and reletive molar mass,
i have learnt about reletive molecular mass, reletive formula mass and reletive atomic mass but never reletive molar mass?
I presume reletive molar mass is somewhat related to molar mass (Mr) as this is the idea wikipedia is giving me... but i dont know whether i should trust it or not.

[HERculina]

wooops sorry to confuse you! i read it wrong and confused myself -.- . yea theres no such thing, its just relative molecular mass. thats the M(r) thing yea?

[Ravit]

yea LOL just released... reletive molecular mass refers to the molar mass of MOLECULES specifically

[WhoTookMyUsername]

I don't really understand the book's explanation of converting Molarity into g / mol.
Here's an example

Convert 0.0024 M NaCl to g/L

the book goes

m=nxM

0.0024 M NaCl means 0.0024 mol NaCl per 1L = (0.0024 mol x 58.44 g /mol) g per 1L

now i understand how to convert M to g/L but i don't really know how to express it as a formula, and m=nM doesn't seem right to me

the way the book does it completely ignores the fact that there's still a random "mass" on the left hand side of the equation that isn't taken into account. Am i missing something or is there a better way of doing it (or both)
thanks

[Hamdog17]

You want C=m/V

:. C(Molarity)=n/V
:. C(grams per litre)=(nM)/V
Or C(grams per litre)=C(Molarity)*M

Just an easy way to remember

[Hamdog17]

From memory you'll use these mostly in the spectrometery area of the course. So that's chapter 7?

[Hamdog17]

Sorry what m=Mn thing?

[WhoTookMyUsername]

I don't really understand the book's explanation of converting Molarity into g / mol.
Here's an example

Convert 0.0024 M NaCl to g/L

the book goes

m=nxM

0.0024 M NaCl means 0.0024 mol NaCl per 1L = (0.0024 mol x 58.44 g /mol) g per 1L

now i understand how to convert M to g/L but i don't really know how to express it as a formula, and m=nM doesn't seem right to me

the way the book does it completely ignores the fact that there's still a random "mass" on the left hand side of the equation that isn't taken into account. Am i missing something or is there a better way of doing it (or both)
thanks

the book uses m= n x M (n = m/M) for this,

[Phy124]

Since you already have, , you need to multiply by to get

Not sure if that's what you're asking?

edit: hold on stuffed up tex