Need Help with Chemistry

[Harkdawg]

lol, i went over moles last week and every calculation in relations to them. Stuff was so easy and clear, i never looked at it like this when i was in 9th grade. :)

[gunner154]

Moles is easy. Just get the ratio from a balanced equation, and you should be on your way. :D

[Phoenix]

However, something baffles me. Phoenix used 450g/200g=2.25. Why do you use this?

The second step is equally baffling. Perhaps you would like to explain your solution? In fact, I find it erroneous that 450g is even considered. What does 200g of solution stand for? 200g of water? Or 200g of sugar+water? It's not correct to consider the maximum mass that dissolves and assume it to be the mass of the sugar dissolved, because temperatures can be higher, so what's the max? And besides, the question didn't say that's the mass dissolved. You need to know the volume of water in the solution in order to use the graph, and if you don't have the total mass of sugar in the solution, you cannot find out how much water is used, and thus you can't solve the question. Thus, I assume that 200g of solution refers to 200ml solution, and since density of water is 1g/cm3, the volume of the solution is 200ml. That makes more sense.

Solution (as the name refers)= water and sugar.

But in the graph you see the amount of sugar disolved in 100 grams (or 100ml) of water.. (note that water has the optimal density... 1Liter = 1 Kilogram so 100 gram = 100 ml)

So what in your y-axis stands are the grams of sugar wich will disolve in 100 grams of water at the temperature marked on the x-axis

about that 450g/200g=2.25

yes taht would be correct, BUT thats not what the exercize wants. There is 200 g of sugarsolution not 450 g (350 g of sugar wich is maximum wich solves in 100g of water at 80 degrees). So there is just 200 g of solution not 450 at 80 degrees, thats why it has to be done a little diffrent.

That makes it you can count straight through..

So if you want 200 grams instead of 450,  you divide those 2.

Then you get a value and you can divide the 160 grams I got to also by that value.

[gunner154]

Ah, I get it. Thanks :) I had to look at it from another point of view (the calculation leading to 2.25 confused me 'cause that's not the way I normally do it). I would divide 160 by 450 (actually it's 460) and then multiply it by 200 :)

I guess my whole analysis is wrong. We DO know what's the hypothetical mass after all. I suppose "palled" means "saturated?"

Yeah. It's correct. Though I think 460 would get you a more accurate answer, closer to 70 than 450. 69.5g is my calculation :)

[Phoenix]

yeah ok, but then you have the nice symbol of "~"  wich means (as you probably know) approximately.

Ah yea, actually its like an = but then with 2 of ~ above eachother...

your calculation is also true, but when you got an index like i did, you can calculate all things by that index instead of repeatedly do that whole formula...

[Harkdawg]

Ok, another problem.

About chemical connections. So elements with 1-3 electrons on their outer layer give up electrons with ease and elements with 6-7 electrons in their outer layer add electrons with ease. And then there are nice examples given to me with hydrogen atom's , ONLY EXAMPLES With elements with 1 + 7. Now what i mean is they tell me that Flour has 7 electrons in outer layer and Hydrogen 1, so there is polar (dont know the word in english - kovalentne - ) connection , Flour gets 8 electron outer layer. Everything is nice and cool, so lets move on K + Cl , potassium has again 1 electron in outer layer and chlorine has 7, so there is ionic connection, both elements get nice 8 electron outer layer.

Now comes the exercizes when they tell me to explain how the connections are happeing between the following elements.

Now it was nice and cool with 1+7 or 2+6 or 3+5 schemes, but what about Ca + F ???????? Ca has 2 electrons in outer layer and F has 7, what is going to happen ? Obviously there is ionic connection. Does F add 1 electron and Ca gives 1 and stays with an outer layer of 1 electrone ? If so how can it be ? Ca has a electron pair in outer layer , in s orbital , Ca +20 | 2 ) 8 ) 8 ) 2 )

1s2 2s2 2p6 3s2 3p6 4s2  , a complete electron pair not 2 single electrons  while F + 9 | 2 ) 7 )

1s2 2s2 2p5 has 3 pairs of electrons and 1 single in outer layer.

Whats gonna happen ?!?!?! im lost again. was nice and cool with all the book examples of 1+7 or 2+6, but    2 + 7 ????????? or 3+6 ?????? or 3+ 7 ???????

Like Al + Cl ?????+ Al has 3 electrons in outer layer and Cl 7 whats gonna happen when they get connected ? How will the outer layers look like ?!?!!?!?

hjalp!

[gunner154]

Ionic compounds are not restricted to the AB format. If Ca and F were to form ionic bonds, you would have one calcium atom donated one electron to each of the fluorine (not flour :)) atoms, and thus you would have CaF2. Of course, the structure is not your simple ionic lattice anymore, but I haven't found out what the alternate arrangement is.

It is slightly different with aluminium and chlorine. Aluminium forms a covalent bond with chlorine, and with its 3 outer electrons, it forms 3 bonds. Each of the chlorine atoms complete octet, but not aluminium.

Note: Actually, AlCl3 is only the empirical formula. If you have studied dative/coordinate bond formation, you would like to note that AlCl3 exists as a Dimer. Aluminium forms 3 bonds, and thus it still hasn't completely occupied its 3rd principal quantum shell. Thus, it forms a dative/coordinate bond with a chlorine atom in another AlCl3 "molecule", so to speak, whereby the chlorine atom contributes both electrons to form a bond with the Al from another "molecule". Thus, AlCl3 exists as a covalent compound with molecular formula Al2Cl6.

[Harkdawg]

i think i got it with ca and f , although the aluminum part was a mystery due to too many terms i dont understand in english :)

but just to make sure, if Ca and F react, so its not 1 atom of Ca and 1 atom of F that react , rather "loads" of em and the ratio will be to 1 Ca Ion there will 2 F Ions ?

[gunner154]

About the 1 Ca ion and 2 F ions part, yes, you are right. The "loads" of them is true for all ionic compounds though. Even K+ and Cl- will come in loads of them. It's called a "crystal lattice" structure. Your crystal salt (it DOES exist, right?) does not comprise one sodium ion and one chloride ion, but rather loads of them in the 1:1 ratio.

If you have learnt dative (coordinate) bonding, you'll get the AlCl3 part though. For now, either take it as just AlCl3, or accept that in reality, it's Al2Cl6, if you're needed to talk about the compound. Do note, however, that it's a covalent compound, not ionic, for AlCl3. This is because Aluminium is so close to the metal/non-metal line that it tends to feature qualities of both metal and non-metal.