Chemistry qn
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Yes noobs like me have qns pretty early in the game.
Bascially, would the mass of a compound be equal to the mass of its constituents after a chemical seperation process. If no and only no, how do i appraoch the qn below?
I think this is O level stuffs:
0.4764 of a sample of an oxide of iron was reduced by a stream of carbon monoxide. 0.3450g of iron metal remained after reduction. What is the empirical formula of the oxde? [fe=58.8 o=16]
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Yep. This is 'O' level question. I'll leave it to you guys (lots of 'O' level Chem students lurking here in this forum) to solve. No fun if I keep spoonfeeding answers. Hint : algebra is your good friend.
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is your ''yep'' for the first qn?
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Theoritically, it's possible for some reaction to achieve what you've stated in paragraph one. When total amount of energy from absorb in bond breaking of the reactant is equal to total energy release from bond forming of products.
hint hint.
(1)FexOy + (2)CO --> (3)Fe + (4)CO2.
1,2,3,4 denotes number of mole.
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While matter and energy can be interconverted to each other, this occurs only under exceptional circumstances (eg. nuclear explosions, Large Hadron Collider particle accelerator, etc).
As far as normal chemical reactions (ie. all reactions in the 'O' and 'A' level syllabuses) are concerned, the mass of the reactants exactly equals the mass of the products, regardless of enthalpy (and entropy) loss or gain during the reaction. If this were not so, you would not be able to correctly balance any chemical equations at all!
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E=mc^2.....familiar?
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Since 21/m/playboy would rather poke fun instead of helping poor davidche, here's a further hint for davidche :
For compound FexOy.
Find no. of moles of the iron oxide in terms of x and y, using the formula [No. of moles = sample mass / molar mass].
Next, Sample mass of iron = (no. of moles).(x).(molar mass of Fe) = 0.3450g.
You would obtain an equation with 2 algebraic variables x and y. Make (x/y) the subject, and you would obtain the numerical value of 0.75, hence the compound is Fe3O4, which is actually a complex of FeO (iron(II) oxide) and Fe2O3 (iron(III) oxide).
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wth.
If you want, here goes.
Hadrons, such as sub-atomic particles, are formed by quarks.
Quarks, depending on their interactions, can annihilate each other and actually form photons.
Poof!
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But this is exceptional because hadrons within an atom are stable.....
Consider this: A neutron outside of an atom has only a half-life of 15 min.
Thus said, what ultima just said is ultimately correct in that sense.
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^ I don't think it is related to the question...
mass of product = mass of reactants because of the balancing of chemical equations.. since matter cannot be created or destroyed.
david, didn't you take your Os last year?
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Originally posted by UltimaOnline:
While matter and energy can be interconverted to each other, this occurs only under exceptional circumstances (eg. nuclear explosions, Large Hadron Collider particle accelerator, etc).
As far as normal chemical reactions (ie. all reactions in the 'O' and 'A' level syllabuses) are concerned, the mass of the reactants exactly equals the mass of the products, regardless of enthalpy (and entropy) loss or gain during the reaction. If this were not so, you would not be able to correctly balance any chemical equations at all!
yar! >.<" Opps. I was doing another question just now. =.="
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Originally posted by Garrick_3658:
david, didn't you take your Os last year?
Now now Garrick, go easy on poor David...
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Originally posted by Garrick_3658:
^ I don't think it is related to the question...
mass of product = mass of reactants because of the balancing of chemical equations.. since matter cannot be created or destroyed.
david, didn't you take your Os last year?
Did you read my post? -
lol sry for the rather late reply. If the answer for the first qn is yes, then i knowhow to do the qn.
I posted the qn under the assumption tat mass is not equal. So if it is equal, then i know how to do. Thanks. And year, im a needy student. Need to buy second hand calculator and textbooks :(
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I quote from my first post
If no and only no, how do i appraoch the qn below?
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Originally posted by davidche:
lol sry for the rather late reply. If the answer for the first qn is yes, then i knowhow to do the qn.
I posted the qn under the assumption tat mass is not equal. So if it is equal, then i know how to do. Thanks. And year, im a needy student. Need to buy second hand calculator and textbooks :(
For reactions like that, you can take it as the mass at the beginning will still be the same at the end of it.Like what an earlier post said, if the masses are not equal then why do you have to balance the equation? By balancing equations, you can can see that the different numbers of atoms will not change after the reaction.
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how to solve this qn?
sulphuric acid reacts with ammonia to form ammonium sulphate.
if 1 kg of sulphuric acid and 2 kg of ammonia are mixed together and reacted. what is the max mass of ammonium sulphate obtained?
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must convert mass of reactants to amount of reactants in mol.
1 kg of H2SO4 = 1000 g of H2SO4 = (1000)/(2+32+64)= 1000/98 = 10.204 mol
2 kg NH3 = 2000 g = 2000/(14+3) = 117.647 mol
Equation: 2NH3 + H2SO4 ----> (NH4)2SO4
Therefore it is quite clear NH3 is in excess; H2SO4 is limiting reagent
Max mass of (NH4)2SO4 = 10.204 mol = 10.204(28+8+32+64) = 1346 g = 1.35 kg
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hey thanks yah! (: but er the answer is 2.69kg. is the answer provided wrong then?
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ya. the answer is wrong. btw got another two questions, can any one just briefly list the steps to arrive at the answer? thanks ((((:
1. Chromium can be extracted from its chromium(III) oxide by the Thermit Reaction.
2Al + Cr203 -> 2Cr + Al2O3
Calculate the percentage yield when 180g of chromium are obtained from a reaction between 100g of alumnium and 400g of chrimium(III) oxide?
2. A hydrocarbon was burnt completely and the products were bubbled into excess of Ca(OH)2 solution. the resulting mixture was filtered and the residue dried and weighed. The weight of the residue was found to be 10.00g. In a seperate experiment, the same amount of hydrocarbon was burnt and the mass of water produced was 2.25g. Determin the empirical formula of the hydrocarbon.
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Originally posted by chocolates-xed:
ya. the answer is wrong. btw got another two questions, can any one just briefly list the steps to arrive at the answer? thanks ((((:
1. Chromium can be extracted from its chromium(III) oxide by the Thermit Reaction.
2Al + Cr203 -> 2Cr + Al2O3
Calculate the percentage yield when 180g of chromium are obtained from a reaction between 100g of alumnium and 400g of chrimium(III) oxide?
2. A hydrocarbon was burnt completely and the products were bubbled into excess of Ca(OH)2 solution. the resulting mixture was filtered and the residue dried and weighed. The weight of the residue was found to be 10.00g. In a seperate experiment, the same amount of hydrocarbon was burnt and the mass of water produced was 2.25g. Determin the empirical formula of the hydrocarbon.
1. Find the limiting reagent in this case by calculating the number of moles. Then calculate the theoretical yield from the balanced equations. Then use the 180g and the theoretical yield, should be able to find the answer.
2. Ca(OH)2 reacts with the CO2 from the combustion to produce CaCO3. So I think the 10.00g is CaCO3. Find the balanced equation then work backwards to find the number of mole of CO2 produced. Then with the number of mole of water produced, you should be able to find the empirical formula using the standard combustion balanced equation.
I think so. Haha.
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er. can anyone do out? cos i don't really understand ):
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Ca(OH)2 + CO2 --> CaCO3 + Water.
The balanced equation. Then use the 10.00g find the number of moles of CaCO3, let it be Q. So since it's 1:1, means number of mole of CO2 produced from the combustion is also Q.
Then mass of water is 2.25g, with it, the number of moles of water produced from the combustion is 2.25g divided by Mr of water.
The standard combustion balanced equation being:
CxHy + (x+y/4)O2 --> (x)CO2 + (y/2)H2O
Equate them together to find x and y lor. You should be dealing with nice numbers lah. Haha.
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Originally posted by chocolates-xed:
1. Chromium can be extracted from its chromium(III) oxide by the Thermit Reaction.
2Al + Cr203 -> 2Cr + Al2O3
Calculate the percentage yield when 180g of chromium are obtained from a reaction between 100g of alumnium and 400g of chrimium(III) oxide?
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Originally posted by d3sT1nY:
Find the limiting reagent.
100g/13 = number of mole of Al = 7.962mol
400g/96 = number of mole of Cr2O3 = 4.167mol
Since 2Al:1Cr2O3, that means Al is the limiting reagent because you will need 4.167X2 worth of Al for complete reaction.
So only 7.962mol of Cr will be produced.
Thus mass of Cr = 7.962 X 24 = 191.089g
Thus % yield = 180/191.089 X 100% = 94.2%
% yield being actual yield over theoretical yield.
Correct me if I'm wrong. Edited.
Oops press wrongly.