CHEM AND BIO HELP AND TIPS HERE

[nid404]

hmm....

Past papers is the key....but learn ur base concepts well
Any problems, ur more than welcome to post here

[Saladin]

yes....

do past-papers a lot

and if u have any problems

be sure to post them here: https://studentforums.biz/index.php/topic,4425.495.html

i can help u pretty much with all subjects

[sarasa]

I have a doubt in Biology paper 6 O/N/07,  in Q1 (b) (ii) it is written in da mark scheme : agitate the same, what do u mean by this. Can anyone tell me what is a  buffer?
Finally, can u write a model answer for it, i just don't get the question ? Thank u in advance!

[nid404]

I have a doubt in Biology paper 6 O/N/07,  in Q1 (b) (ii) it is written in da mark scheme : agitate the same, what do u mean by this. Can anyone tell me what is a  buffer?
Finally, can u write a model answer for it, i just don't get the question ? Thank u in advance!

the point u mentioned is followed by increase in range of pH tested....this means u carry out the same procedure to obtain the desired result for the new temperatures...

Buffer is an ionic compound that resists change in it's pH. So, when u use a buffer, u ensure that there is no change in pH...thereby maintaining the desired pH(making the results more reliable)

[ruby92]

Thank You 

[DEGO]

hey cn any one hlp me understand the calculations chemistry (olvl)

[holtadit]

hey cn any one hlp me understand the calculations chemistry (olvl)

Be specific. Post a question that you dont understand and I ll help you.

[DEGO]

Be specific. Post a question that you dont understand and I ll help you.

  the solving confuse me when i solve a question  i get confused which rule to use

[holtadit]

 the solving confuse me when i solve a question  i get confused which rule to use

Okay for gases use the following:

moles of gas = volume of gas/24000                 NOTE: use 24000 when volume in cm^3 and use 24 instead when volume is in 24 dm^3

For liquids use::

moles of liquid= (volume of liquid in cm^3 * concentration in mol/dm^3) / 1000

For solid use:

moles = mass in grams/mass number of element           NOTE: if its a solid compound then add up the mass nos. of each element

[nid404]

Thank You ari

[holtadit]

An aqueous solution contains barium iodide.

It is possible to obtain a solution that contains Ba2+(aq) but no I–(aq) by adding ……1…… until no
more ……2…… precipitate forms.

Which words correctly complete gaps 1 and 2?
           1                                      2
A) aqueous lead(II) nitrate              white
B) aqueous lead(II) nitrate              yellow
C) dilute sulphuric acid                    white
D) dilute sulphuric acid                    yellow

FROM WINTER 2008 Paper 1
------------------------------------------------------------------------------------------------------------------------------------
I don't understand how the answer could be B. Because if BaI2  reacts with Lead Nitrate u get Lead Iodide (hence the presence of I ions) and u get Barium Nitrate.

Actually in both reactions you would get I ions and Barium ions.

HELP !

[nid404]

They want only Ba2+ ions in the solution....which means they want iodide to ppt off....
so to do that, you add lead nitrate...lead iodide precipitates off and the solution contains BaNO3..
Gettin it?

[holtadit]

I would just like to take this moment to say...



I LOVE CHEMISTRY !

[DEGO]

Okay for gases use the following:

moles of gas = volume of gas/24000                 NOTE: use 24000 when volume in cm^3 and use 24 instead when volume is in 24 dm^3

For liquids use::

moles of liquid= (volume of liquid in cm^3 * concentration in mol/dm^3) / 1000

For solid use:

moles = mass in grams/mass number of element           NOTE: if its a solid compound then add up the mass nos. of each element

Thank You ur the best

[DEGO]

An aqueous solution contains barium iodide.

It is possible to obtain a solution that contains Ba2+(aq) but no I–(aq) by adding ……1…… until no
more ……2…… precipitate forms.

Which words correctly complete gaps 1 and 2?
           1                                      2
A) aqueous lead(II) nitrate              white
B) aqueous lead(II) nitrate              yellow
C) dilute sulphuric acid                    white
D) dilute sulphuric acid                    yellow

FROM WINTER 2008 Paper 1
------------------------------------------------------------------------------------------------------------------------------------
I don't understand how the answer could be B. Because if BaI2  reacts with Lead Nitrate u get Lead Iodide (hence the presence of I ions) and u get Barium Nitrate.

Actually in both reactions you would get I ions and Barium ions.

HELP !

its B  because its test for anion and cation he is testing for iodine tht form yellow ppt whn (acidified leadnitrate) is added got it?XD