AS level bio

[alihaiderrrt]

http://papers.xtremepapers.com/CIE/...nd AS Level/Biology (9700)/9700_s07_qp_32.pdf plz solve question 1 b i)(the recroding of data one),,plz plz plz plz plz plz plz plz plz plz plz reply back!

 

[Alice123]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Biology (9700)/9700_s07_qp_32.pdf plz solve question 1 b i)(the recroding of data one),,plz plz plz plz plz plz plz plz plz plz plz reply back!

its been a long time i've given my practicals.. do u hav the coursebook?? u can find serial dilution there, if nt pm me

 

[alihaiderrrt]

coursebook??the A level book by mary jones,right???

 

[Warrior66]

Asalam-o-Alaikum!
For b) i) you have to draw a table in which there are three columns- one for the solutions of different concentrations, then one for the color change & the other for the actual results (optional).
To make serial dilutions from 0.8% solution of glucose, it goes as such:
1. we already have 0.8%
2. 0.08% -- 1 cm3 of 0.8% sol. + 9 cm3 of distilled water
3. 0.008% -- 1 cm3 of 0.08% sol. + 9 cm3 of distilled water
4. 0.0008% -- 1 cm3 of 0.008% sol. + 9 cm3 of distilled water
5. reducing sugar in a fruit juice, labelled F1
so first start off by writing labels and then sticking them on the test-tubes and then make the serial dilutions- ready to start testing it with the Benedict's solution.

 

[sam1234]

Asalam-o-Alaikum!
For b) i) you have to draw a table in which there are three columns- one for the solutions of different concentrations, then one for the color change & the other for the actual results (optional).
To make serial dilutions from 0.8% solution of glucose, it goes as such:
1. we already have 0.8%
2. 0.08% -- 1 cm3 of 0.8% sol. + 9 cm3 of distilled water
3. 0.008% -- 1 cm3 of 0.08% sol. + 9 cm3 of distilled water
4. 0.0008% -- 1 cm3 of 0.008% sol. + 9 cm3 of distilled water
5. reducing sugar in a fruit juice, labelled F1
so first start off by writing labels and then sticking them on the test-tubes and then make the serial dilutions- ready to start testing it with the Benedict's solution.

Are we supposed to take 4 dilutions only? or more than 4?

 

[alihaiderrrt]

Asalam-o-Alaikum!
For b) i) you have to draw a table in which there are three columns- one for the solutions of different concentrations, then one for the color change & the other for the actual results (optional).
To make serial dilutions from 0.8% solution of glucose, it goes as such:
1. we already have 0.8%
2. 0.08% -- 1 cm3 of 0.8% sol. + 9 cm3 of distilled water
3. 0.008% -- 1 cm3 of 0.08% sol. + 9 cm3 of distilled water
4. 0.0008% -- 1 cm3 of 0.008% sol. + 9 cm3 of distilled water
5. reducing sugar in a fruit juice, labelled F1
so first start off by writing labels and then sticking them on the test-tubes and then make the serial dilutions- ready to start testing it with the Benedict's solution.

But in the mark scheme it says that one value must be above 0.2 and one below it???what does this mean?

 

[alihaiderrrt]

Are we supposed to take 4 dilutions only? or more than 4?

i think 3-5 dilution are fine!

 

[Warrior66]

well in that case you can't carry out serial dilutions..what you'd have to do is
1. 0.8%
2. make 0.6% by using 7.5 cm3 of 0.8% sol. with 2.5cm3 of distilled water.
3. make 0.4% by using 5 cm3 of 0.8% sol. with 5 cm3 of distilled water.
4. make 0.2% by using 2.5 cm3 of 0.8% sol. with 7.5 cm3 of distilled water.
5. just use distilled water since the conc. is obviously 0.00% !
Note: why do we have to do this instead of serial dilutions is because lets be realistic, no fruit juice sample can have such a low conc. of glucose like: 0.08%, 0.008%, 0.0008%!! So, in this case, it's better to use this method instead.

 

[Warrior66]

Are we supposed to take 4 dilutions only? or more than 4?

It's probably OK to use 3-4 dilutions but since we're only provided with 5 test-tubes, we have to make do with what they have provided. In the mark scheme, it says: "at least three different dilutions tested" ---> so there's no problem if you wish to carry out more but keep in mind, the clock is ticking!

 

[alihaiderrrt]

thank you!u made it really easy!u going for distinction?

 

[alihaiderrrt]

when we will draw out some volume from the original 10 cm^3 solution(0.8 mol dm^3).the volume will decrease.so do we have to fill the test tube with water to make it 10 cm^3 again.e.g if i remove 3 cm^3 of water......do i have to put 3cm^3 to make it 10 cm^3 again?

 

[Warrior66]

when we will draw out some volume from the original 10 cm^3 solution(0.8 mol dm^3).the volume will decrease.so do we have to fill the test tube with water to make it 10 cm^3 again.e.g if i remove 3 cm^3 of water......do i have to put 3cm^3 to make it 10 cm^3 again?

No, there's no need to do that...
1. If we take this question as an example, the 0.8% solution provided will be sufficient for your use. It will be given in a small beaker and the quantity will be definitely more than just 10 cm3. Perhaps 20 cm3 or so. So when you carry out the dilutions as described above, you will take the required amount each time to put into each test-tube labelled '0.6%' , '0.4%' , '0.2%' and afterwards, use a syringe to take 10 cm3 of 0.8% and put it into a test-tube labelled '0.8%'.
Remember: It is NOT necessary that you use 10 cm3 of each sol. to carry out the experiments with. I would suggest that you use labelled beakers to make the dilutions and then take 1.0 cm3 of each sol. and put it into the test-tubes. And then you can continue with the Benedict's test.
2. To make serial dilutions that decrease by ten fold each time (e.g: 8%, 0.8%, 0.008%), don't worry about the decrease in the volume of the previous solution because after we're done with the serial dilutions, we will only use 1.0 cm3 of each concentration for the experiment.
Hope this helps!

 

[alihaiderrrt]

great!.one last question.if u do take a certain a amount of volume(take 5 cm3) from a given sucrose solution lets say(10 cm3 of 0.6 mol dm3)..does this effect the molarity of the solution(0.6 mol dm3)

 

[Warrior66]

thank you!u made it really easy!u going for distinction?

No problem! Well..I never really got a distinction..!

 

[Warrior66]

great!.one last question.if u do take a certain a amount of volume(take 5 cm3) from a given sucrose solution lets say(10 cm3 of 0.6 mol dm3)..does this effect the molarity of the solution(0.6 mol dm3)

No, it wouldn't. Because see, the concentration of a sucrose solution would be the amount of sucrose in moles present in the solution. So when we take 5 cm3 away from 10 cm3, we're not only taking the solvent, we're taking the solution which is solute + the solvent. So some moles of sucrose will also be taken away to balance the ratio once again and the 5 cm3 of sucrose solution left over will have a conc. of 0.6 mol dm^-3.

 

[sam1234]

No, it wouldn't. Because see, the concentration of a sucrose solution would be the amount of sucrose in moles present in the solution. So when we take 5 cm3 away from 10 cm3, we're not only taking the solvent, we're taking the solution which is solute + the solvent. So some moles of sucrose will also be taken away to balance the ratio once again and the 5 cm3 of sucrose solution left over will have a conc. of 0.6 mol dm^-3.

while making a table in serial dilution do we mention that for eg 5cm3 volume was taken from previous solution. or we leave it as it is?

 

[Warrior66]

It'd be better to show/mention everything when you make the serial dilutions.

 

[sam1234]

but we cant give a heading to each and every column?

 

[Warrior66]

Ok, firstly they never do tell you to make a table for the serial dilutions...you may have to draw it out but I haven't come across any past exam that says to draw a table. :/

 

[mrnt3250]

Ok, firstly they never do tell you to make a table for the serial dilutions...you may have to draw it out but I haven't come across any past exam that says to draw a table. :/

They will indirectly say, prepare the space below for the results of your experiment..