CHEM AND BIO HELP AND TIPS HERE

[jellybeans]

Just follow the equation:
2Na            +              S -------->     Na₂S
46                              32                        
11.5                            10(but excess so we wont use this)
We know that 11.5g of Na reacted .. so just use the simple formula .. mass/RFM .. 11.5/23 = 0.5moles

um um um.. wait so even if its 2Na .. it's still gonna be 0.5moles?  
isn't 0.5 for 1Na? 

[MasterMath]

um um um.. wait so even if its 2Na .. it's still gonna be 0.5moles?  
isn't 0.5 for 1Na? 

You ignore the equation.. You have 11.5g of Na in  your hands .. and they react .. so how many moles that were in your hands reacted?
11.5/23 .. Dont let the balancing of the equation mix you up..

[jellybeans]

You ignore the equation.. You have 11.5g of Na in  your hands .. and they react .. so how many moles that were in your hands reacted?
11.5/23 .. Dont let the balancing of the equation mix you up..

OHHHHHHHH. so the 2Na's just to tell you that if you need to find the mole for the reacted Sulphur, you divide 0.5/2 ..?

[Ivo]

can somebody answer these questions and please tell me y??

thanks

The answer to your first question is B, because it asks for passage of water, so water is always lost by transpiration (water vapour diffuses out of plant through stoma).

Second question is A, general rule, both atria contract at the same time, both ventricles contract at the same time.  The only given option for this rule is A, because there is no option for Z and Y.

[CatAly$t]

can somebody answer these questions and please tell me y??

thanks

mmm...anybody please explain to me the questions on my previous post....

it's on the previous page...

[Ivo]

mmm...anybody please explain to me the questions on my previous post....

it's on the previous page...

I've answered it, please check the mark scheme and tell me if I am right.

[CatAly$t]

The answer to your first question is B, because it asks for passage of water, so water is always lost by transpiration (water vapour diffuses out of plant through stoma).

Second question is A, general rule, both atria contract at the same time, both ventricles contract at the same time.  The only given option for this rule is A, because there is no option for Z and Y.

ooohh....sorry man....didnt see it...

yeah,ur right...

thx  for the explanation

[Ivo]

Hiiii, um there doesnt seem to be any answers to Q5 onwards in the MS for M/J 02.

http://freeexampapers.com/FreeExamPapers.com_.php?__lo=SUdDU0UvQ2hlbWlzdHJ5L0NJRS8yMDAyIEp1bi8wNjIwX3MwMl9tc18zLnBkZg==

i've tried xtreme papers as well..
help?

thaaanks

All of Q5 has been answered previously, I hope this is good enough, obviously not the mark scheme though! 

the a) part?

Liquids take the shape of the container, they maintain their volume. The intermolecular forces in liquids are significant and therefore, they do not expand to occupy all the space available (as gases do). A given mass of liquid has a fixed volume. also molecules in liquid have less k.e as compared to that of gases.Particles in gases have very weak intermolecular forces and high kinetic energy, hence the particles move independent of each other and occupy the space available to them.

b)i) rate= time and volume. In other words, its the volume produced and the time taken.

ii) CO2 due to lower molecular mass. or less density

The equation you need to use is:

                      Volume of gas (in dm³)
Moles of gas = --------------------------
                                      24

Note to convert cm³ to dm³, divide quantity by 1000 (e.g. 20cm³/1000=0.02dm³)

This is the proper theory and equation behind my calculations below.

Here are the answers for 5) c) as requested:

i)   Moles of C₄H₆: 0.02/24=0.000833
     From equation, we know 2 moles of C₄H₆ reacts with 11 moles of O₂
     Therefore, moles of O₂: 0.000833*5.5=0.00458
     Therefore, volume of O₂: 4.58*24*1000=110cm³

ii)  From equation, we know 2 moles of C₄H₆ produces 8 moles of CO₂
     Therefore, moles of CO₂: 0.000833*4=0.00333
     Therefore, volume of CO₂: 0.00333*24*1000=80cm³

iii) From equation, we know 2 moles of C₄H₆ produces 6 moles of H₂O
     Therefore, moles of H₂O: 0.000833*3=0.0025
     Therefore, volume of H₂O: 0.0025*24*1000=60
     Therefore, total volume of gases is simply volume of CO₂ + volume of H₂O:
     80+60=140cm³

     Alternatively, 8+6=14, so 2 moles of C₄H₆ produces 14 moles of products
     Therefore, moles of products: 0.000833*7=0.00583
     Therefore, volume of products: 0.00583*24*1000=140cm³

For part d), you use this formula:

             Mass
Moles = ------
               M_r

d)  From the above equation, 1 mole of butyne forms 3 moles of water
     Number of moles of butyne reacted: 9/54=0.167
     Number of moles of water formed: 0.167*3=0.5
     Mass of water formed: 0.5*(2+16)=9g

I hope this has helped.

[jellybeans]

All of Q5 has been answered previously, I hope this is good enough, obviously not the mark scheme though! 

hahaha. thanks,

[jellybeans]

HOW DO YOU DRAW FREE MOVING ELECTRONS IN AN ALLOY?  
do you draw '-' signs in the atoms? Lol xD

[Ivo]

HOW DO YOU DRAW FREE MOVING ELECTRONS IN AN ALLOY?  
do you draw '-' signs in the atoms? Lol xD

This website gives a good explanation about structure of alloys.  Enjoy

http://www.gcsescience.com/ex29.htm

[Helium]

Can someone show his way of calculation for this Question, plz

[Ivo]

Can someone show his way of calculation for this Question, plz

OK right, here goes:

i)  Moles of butane: 0.01/24=0.000417
    From the equation, 1 mole of butane reacts with 6.5 moles of oxygen
    Therefore, 0.000417*6.5=0.00271
    So volume of oxygen reacted: 0.00271*24*1000=65cm³
    Therefore, volume of oxygen left: 100-65=35cm³

ii) From the equation, 1 mole of butane gives 4 moles of carbon dioxide
    Therefore, 0.000417*4=0.00167
    So volume of carbon dioxide formed: 0.00167*24*1000=40cm³

That was the technical way of doing it.  Here is a simply way, but only applies if calculations involve gases only:

Consider this formula:

                      Volume of gas (in dm3)
Moles of gas = --------------------------
                                      24

Because we know one mole of gas occupies 24dm³ at r.t.p., therefore we can go about it this way:

i)  From the equation, 1 mole of butane reacts with 6.5 moles of oxygen
    So, 10cm³ of butane reacts with 10*6.5=65cm³ of oxygen
    Therefore, volume of oxygen left: 100-65=35cm³

ii) From the equation, 1 mole of butane gives 4 moles of carbon dioxide
    So 10cm³ of butane gives 10*4=40cm³ of carbon dioxide

However, the way I've gone about it using ratios can only be applied to gas volumes calculations, as explained above.  For a lot of the others, you'll still need to apply the formula:

             Mass
Moles = ------
               Mr

If you still don't get it, let me know!  

[The Golden Girl =D]

people there is smthn i wanna kno ........when r hydrocarbons solids , and when r they liquid and when r they gases? ....

[Meticulous]

people there is smthn i wanna kno ........when r hydrocarbons solids , and when r they liquid and when r they gases? ....

Usually, small chained hydrocarbons are gases, and the state changes from gas to liquid to solid as the chain length increases.

Eg: methane--> gas

hexane--> liquid