Post by: andy456 on January 14, 2010, 02:40:18 pm
I just need help with this question. I know that its really simple but its just not working out for me.
Any help is appreciated
Calculate the amount (in mole) of:
Cl ions in 13.4g of nickel chloride (NiCl2)
Post by: the.watchman on January 14, 2010, 02:45:21 pm
As there are two chloride ions in each molecule of nickel chloride, there is 0.2068mol of Cl ions.
I have only got a headstart on chem and not done any at school, so if I'm wrong, please let me know!
Post by: xD_aQt on January 14, 2010, 02:46:41 pm
Well usingHaha, damn you beat me to it! :)with
and
for NiCl2,
As there are two chloride ions in each molecule of nickel chloride, there is 0.2068mol of Cl ions.
I have only got a headstart on chem and not done any at school, so if I'm wrong, please let me know!
Post by: andy456 on January 14, 2010, 02:47:27 pm
Its like simple revision but I just couldnt get it....
I guess thats what happens when you havent done chemistry in like 3 months
Post by: xD_aQt on January 14, 2010, 02:48:22 pm
Nah thats right, thanks....You should be alright! Not too late to revise
Its like simple revision but I just couldnt get it....
I guess thats what happens when you havent done chemistry in like 3 months
Post by: andy456 on January 14, 2010, 02:49:17 pm
Its pretty much revision off last year.... nothing new yet
Post by: the.watchman on January 14, 2010, 02:50:32 pm
Yeah im just going through the first 4 chapters of my text book....
Its pretty much revision off last year.... nothing new yet
Good luck! I just covered a few chapters of Chem Unit 1
Post by: andy456 on January 14, 2010, 02:52:15 pm
Post by: xD_aQt on January 14, 2010, 02:56:20 pm
I hated chem 1..... it took so long for me to understand mole+1 me too ;)
Post by: andy456 on January 14, 2010, 03:10:28 pm
Post by: andy456 on January 15, 2010, 12:48:31 am
Determine the percentage composition of the following compound
Lead (IV) oxide (PbO2)
So I used the empirical formula method to determine:
207.37/239.3688 : 31.9988/239.3688
0.866 : 0.134
86.6% : 13.4%
The answer in the book is 13.4% but in the question it doesn't specify which ion to find the percentage of so i was wondering if the question just means oxygen, or there was like a typo or something in the book.
Btw the book is Heinmann Chemistry Two
Post by: superflya on January 15, 2010, 12:51:29 am
wording of question is shit.
Post by: Potter on January 15, 2010, 01:00:25 am
I have another simple question......
Determine the percentage composition of the following compound
Lead (IV) oxide (PbO2)
If the question is written like this, calculate the percentages of all the elements. The book probably just got lazy.
Post by: andy456 on January 15, 2010, 01:01:42 am
Yeah do textbooks even make typo's....
Post by: superflya on January 15, 2010, 01:03:52 am
Post by: superflya on January 15, 2010, 01:04:36 am
I think I wrote it wrong in the book it says Lead(IV)oxide (PbO2)...
Yeah do textbooks even make typo's....
A LOT OF TYPOS.
Post by: andy456 on January 15, 2010, 01:05:51 am
It's very misleading as well......
Oh well.... what can you do?
Post by: superflya on January 15, 2010, 01:14:53 am
Post by: andy456 on January 15, 2010, 11:32:33 am
Magnesium reacts with hydrochloric acid according to the equation:
Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)
If 10.0g of magnesium reacts completely, calculate the mass of hydrogen that forms
Post by: xD_aQt on January 15, 2010, 11:42:38 am
I have another question.....
Magnesium reacts with hydrochloric acid according to the equation:
Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)
If 10.0g of magnesium reacts completely, calculate the mass of hydrogen that forms
n =
m = nM = 0.41152263374485596707818930041152 x 2 = 0.82304526748971193415637860082305 g
Post by: andy456 on January 15, 2010, 11:45:41 am
I've done what you did, but i multiplied it by 2 because its H2
Post by: the.watchman on January 15, 2010, 11:46:20 am
I have another question.....
Magnesium reacts with hydrochloric acid according to the equation:
Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)
If 10.0g of magnesium reacts completely, calculate the mass of hydrogen that forms
n ==
= 0.41152263374485596707818930041152
m = nM = 0.41152263374485596707818930041152 x 1 = 0.41152263374485596707818930041152 g
Is that right?
Shouldn't it be 2mol of hydrogen gas?
And please round off to the correct number of sigfigs :P
Post by: andy456 on January 15, 2010, 11:48:22 am
Thats what i did but its still wrong
Post by: xD_aQt on January 15, 2010, 11:48:50 am
Nah, sorry the answer in the back is 0.0824g......does the back say 0.0824 g ? I thought the answer be 0.823 g
I've done what you did, but i multiplied it by 2 because its H2
I will round off .. my bad :PI have another question.....
Magnesium reacts with hydrochloric acid according to the equation:
Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g)
If 10.0g of magnesium reacts completely, calculate the mass of hydrogen that forms
n =
m = nM = 0.41152263374485596707818930041152 x 1 = 0.41152263374485596707818930041152 g
Is that right?
Shouldn't it be 2mol of hydrogen gas?
And please round off to the correct number of sigfigs :P
Post by: andy456 on January 15, 2010, 11:50:09 am
Maybe its just another typo in the book
Post by: xD_aQt on January 15, 2010, 11:51:42 am
Yeah it says 0.0824g but I also got 0.823gHaha, could be! What book is this? Heinemann?
Maybe its just another typo in the book
Post by: andy456 on January 15, 2010, 11:52:42 am
Post by: xD_aQt on January 15, 2010, 11:53:43 am
Yeah its heinemann....... do they make typo's alot cause i found another one yesterday????Yeah, they tend to make a few typo's! Just post up any questions that you think may have a typo in the answer section.
Post by: xD_aQt on January 15, 2010, 11:54:33 am
Post by: andy456 on January 15, 2010, 11:57:19 am
Btw Q14a worked fine.....
and the one from the other day was Chapter 2 Q10 page.18
Have you been studying for chemistry over the holidays?
Post by: xD_aQt on January 15, 2010, 12:00:57 pm
Post by: andy456 on January 15, 2010, 12:02:06 pm
Post by: andy456 on January 15, 2010, 02:39:29 pm
Iron metal is extracted in a blast furnace by a reaction between iron(III)oxide and carbon monoxide:
Fe2O3(s) + 3CO(g) -> 2Fe(l) + 3CO2(g)
To produce 1000kg of iron, calculate the volume of CO2 produced at SLC(25C and 101.3kPa)
Post by: vexx on January 15, 2010, 02:51:30 pm
i may as well attempt:)
n(Fe)=1,000,000/55.9
= 17,889mol
n(CO2)=(3/2) x n(Fe)
n(CO2)=26,883mol
Pv=NRT
v(CO2)=nRT/P
v=26883 x 8.31 x (25+273)/101.3
=655,975 L
sig figs: = 656 kL
Post by: Potter on January 15, 2010, 03:41:30 pm
^
i may as well attempt:)
n(Fe)=1,000,000/55.9
= 17,889mol
n(CO2)=(3/2) x n(Fe)
n(CO2)=26,883mol
Pv=NRT
v(CO2)=nRT/P
v=26883 x 8.31 x (25+273)/101.3
=655,975 L
sig figs: = 656 L
That looks good to me. Though, there's one thing I would've done differently.
Since it's at SLC conditions just multiply n(CO2) by 24.5, it's simple and reduces variables(which may lead to errors)
Post by: vexx on January 15, 2010, 03:45:43 pm
but atleast mine way works with anything that isn't SLC or STP too :P
Post by: crappy on January 15, 2010, 03:49:56 pm
Volume=24.5 x n(?)
at STP:
Volume = 22.5 x n(?)
god, I hate chem
Post by: fady_22 on January 15, 2010, 03:54:56 pm
Post by: Edmund on January 15, 2010, 03:58:02 pm
where Vm is 22.4 L/mol or 24.5 L/mol depending on SLC or STP...
Post by: vexx on January 15, 2010, 03:58:55 pm
Also, be careful with units: you said 656 L. Its 656 kL! :)
oops- thanks for that! changed.
Post by: andy456 on January 15, 2010, 04:09:16 pm
Post by: the.watchman on January 15, 2010, 04:10:27 pm
Just double checking for chemistry do you wait till the very end to round off... right???
For an accurate answer, round off at the very end.
However, you can work through a question either 1 or 2 decimal places more than your final answer will be, that is OK.
Post by: vexx on January 15, 2010, 04:14:59 pm
Just double checking for chemistry do you wait till the very end to round off... right???
For an accurate answer, round off at the very end.
However, you can work through a question either 1 or 2 decimal places more than your final answer will be, that is OK.
yeah,
just keep everything on your calculator
so for example with calculating volume from a gas
find the mol
n=m/M
don't erase the calc !! if it was like 101.15949842 on the screen keep it.
then in the next equation
v=NRT/P
use what was on your calc to continue and times by N x R then dvide by P. then round off at final answer!
most calculations let you do this
Post by: fady_22 on January 15, 2010, 04:17:44 pm
Just double checking for chemistry do you wait till the very end to round off... right???
For an accurate answer, round off at the very end.
However, you can work through a question either 1 or 2 decimal places more than your final answer will be, that is OK.
yeah,
just keep everything on your calculator
so for example with calculating volume from a gas
find the mol
n=m/M
don't erase the calc !! if it was like 101.15949842 on the screen keep it.
then in the next equation
v=NRT/P
use what was on your calc to continue and times by N x R then dvide by P. then round off at final answer!
most calculations let you do this
If your calculator doesn't do this, it would be a good idea to buy a new one.
Post by: andy456 on January 15, 2010, 04:20:48 pm
Post by: vexx on January 15, 2010, 04:22:42 pm
What's a good calc for chem.... cause i have the casio classpad for methods which is great but i have been told i cant use that one in the chem exams
i think/heard from others/been told by the teacher that the SHARP Scientific Calculators are the best for chem/accounting. i have the:
"Sharp EL-531WH - Advanced D.A.L."
Post by: fady_22 on January 15, 2010, 04:25:42 pm
Post by: fady_22 on January 15, 2010, 04:27:34 pm
What's a good calc for chem.... cause i have the casio classpad for methods which is great but i have been told i cant use that one in the chem exams
i think/heard from others/been told by the teacher that the SHARP Scientific Calculators are the best for chem/accounting. i have the:
"Sharp EL-531WH - Advanced D.A.L."
I use the Texas Instruments TI-30XB. Its better than the sharp in my opinion.
Post by: andy456 on January 15, 2010, 04:34:06 pm
Post by: Potter on January 15, 2010, 04:40:45 pm
You can save things in the graphics/CAS.
I use a Casio Fx-82AU. Pretty good calculator and it has been very reliable.
Post by: superflya on January 15, 2010, 06:46:24 pm
best way to keep ur answers as accurate as possible is to use the store function on the calculator and recall the value whenever u need it again. This way, u can simply round off after u have completed ur calculations and almost every scientific calculator should be able to do this.
Post by: kyzoo on January 15, 2010, 07:37:23 pm
You can save things in the graphics/CAS.
You can save things in a scientific calculator as well, just that there are a lot more "slots" on a graphics calculator.
Also graphics calculators can generate graphs, run installed programs, and contains many more functions than a scientific calculators.
Post by: Potter on January 15, 2010, 09:22:39 pm
You can save things in the graphics/CAS.
You can save things in a scientific calculator as well, just that there are a lot more "slots" on a graphics calculator.
Also graphics calculators can generate graphs, run installed programs, and contains many more functions than a scientific calculators.
Sorry, I meant you can save things like apps, formulas, etc..
Post by: andy456 on January 16, 2010, 11:14:01 am
An impure sample of iron(II)sulfate, weighing 1.545g, was treated to produce a precipitate of Fe2O3. If the mass of the dried precipitate was 0.315g, calculate the percentage of iron in the sample.
Post by: xD_aQt on January 16, 2010, 11:19:13 am
Aight got another question....
An impure sample of iron(II)sulfate, weighing 1.545g, was treated to produce a precipitate of Fe2O3. If the mass of the dried precipitate was 0.315g, calculate the percentage of iron in the sample.
Post by: fady_22 on January 16, 2010, 11:24:23 am
=.315/159.7
=1.97*10^-3 mol
n(Fe3+)=1.97*10^-3*2
=3.94*10^-3 mol
m(Fe3+)=n*mr
=3.94*10^-3*55.85
=.22g
% Fe in sample= .22/1.545*100
= 14.3%
Post by: naved_s9994 on January 16, 2010, 03:00:13 pm
What's a good calc for chem.... cause i have the casio classpad for methods which is great but i have been told i cant use that one in the chem exams
i think/heard from others/been told by the teacher that the SHARP Scientific Calculators are the best for chem/accounting. i have the:
"Sharp EL-531WH - Advanced D.A.L."
I use the Texas Instruments TI-30XB. Its better than the sharp in my opinion.
Also TI-82 AU does same as TI-30XB, but it is also cheaper. (Only by $5 or so?)
Post by: andy456 on January 22, 2010, 02:29:21 pm
A 2.203g sample of an organic compound was extracted from a plant. When it was burned in oxygen, the hydrogen in the compound was converted to 1.32g of water and the carbon was oxidised to 3.23g of carbon dioxide.
What is the empirical formula of the compound??
Thanks
Post by: xD_aQt on January 22, 2010, 03:19:36 pm
Hey, i need help with another question..
A 2.203g sample of an organic compound was extracted from a plant. When it was burned in oxygen, the hydrogen in the compound was converted to 1.32g of water and the carbon was oxidised to 3.23g of carbon dioxide.
What is the empirical formula of the compound??
Thanks
Post by: Studyinghard on January 22, 2010, 03:32:11 pm
Hey, i need help with another question..
A 2.203g sample of an organic compound was extracted from a plant. When it was burned in oxygen, the hydrogen in the compound was converted to 1.32g of water and the carbon was oxidised to 3.23g of carbon dioxide.
What is the empirical formula of the compound??
Thanks
I remember doing this question. Is this heineman textbook :P?
Post by: andy456 on January 22, 2010, 04:00:27 pm
I hate empirical formulas
Post by: andy456 on January 23, 2010, 12:46:29 pm
What mass of barium chloride will remain after a 15.0g sample of the hydrated salt BaCl2.2H2O is heated to drive off all the water.
n(BaCl2)= 15.0/208.246
= 0.07203019506mol
n(BaCl2)/n(H2O)= 2/1
n(H2O)= 0.1440603901mol
m(H2O)= 0.1440603901 x 18.01534
= 2.595296908g
15.0g-2.595296908g
= 12.4g
Post by: xD_aQt on January 23, 2010, 12:49:11 pm
Post by: andy456 on January 23, 2010, 12:53:06 pm
Post by: S2paramore on January 23, 2010, 01:18:12 pm
I think it should be:
M(BaCl2 . 2 H2O) = 208.226 + 36.04 = 244.266 g/mol
n(BaCl2 . 2H2O) = 15.0 / 244.266 = 0.0614 mol
n(BaCl2 . 2H2O)= n(BaCl2)= 0.0614 mol
Mass BaCl2 = 0.0614 x 208.226 = 12.8 g
Post by: Edmund on January 24, 2010, 01:55:58 pm
And have the same working as S2paramore/xD_aQt
Post by: andy456 on January 30, 2010, 02:39:22 pm
For a 0.20M solution of potassium sulfate, K2SO4, calculate the amount, in mole, of:
-Potassium ions
-Sulfate ions
-oxygen atoms
Any help would be great
Post by: fady_22 on January 30, 2010, 02:47:18 pm
Post by: cindyy on January 30, 2010, 02:47:35 pm
Post by: cindyy on January 30, 2010, 02:48:34 pm
a n(K2SO4) = C × V = 0.20 × 0.250 = 0.050 mol
n(K+) = 2 × n(K2SO4) = 2 × 0.050 = 0.10 mol
b n(SO42-) = n(K2SO4) = 0.050 mol
c n(S) = n(K2SO4) = 0.050 mol
but doesnt give the volume in the Q
Post by: andy456 on January 30, 2010, 02:53:58 pm
Thanks for your help though guys
Post by: cindyy on January 30, 2010, 02:56:08 pm
Post by: andy456 on January 30, 2010, 03:01:06 pm
Post by: superflya on January 30, 2010, 03:06:10 pm
yeah i am using heinmann as well! but i actually quite like it, and i havent found any mistakes so far :S
there a quite a few questions in the heinemann book with dodgy wording.
Where did you get the solutions from???
look around they were posted up a while back, use the search tool at the top right of ur window.
Post by: cindyy on January 30, 2010, 03:23:59 pm
Post by: andy456 on January 30, 2010, 04:06:29 pm
Post by: cindyy on January 30, 2010, 04:11:10 pm
Post by: Edmund on January 30, 2010, 04:38:02 pm
Post by: cindyy on January 30, 2010, 05:01:28 pm