Chemo P5 tips

[salvatore]

I don't quite understand the relative concentrations and relative volumes stuff. Could someone please explain this to me?

 

[SomeStudent]

A line of best fit can be a line or a curve.

Just check out if the points are coming on a line if they are then well and good and if not see if u have a general curved pattern involving your points if it's there draw the curve and not line and make sure curve is smooth and does not deviate to allow even points that wud not be on line.

Oh okay. Thank you both!

 

[SomeStudent]

I don't quite understand the relative concentrations and relative volumes stuff. Could someone please explain this to me?

I am not really sure about it too but basically if you have to use varying concentrations just keep on adding more water. Like you have 2 mol/dm3 acid and you want to vary its concentration. Do it like this:
Vol of acid 50 40 30 20 10
Corresponding water vol 0 10 20 30 40
Conc 2 1.6 1.2 etc
Just make sure you have the same amount of total vol at each try

 

[Muhammad Zain Qasmi]

When preparing a solution of a fixed concentration from a given parent solution of concentration , say, 2.0 mol/dm3

A. We are required to prepare a solution of concentration of 1.0 mol/dm3 with volume 250 cm3 ( the concn cannot be greater than 2 !!!!!!!!!!!!!!)
a. Add 100 cm3 of the parent solution to a volumetric flask of marking at 250 cm3
b. Top off with water to the mark of 250 cm3. Use a wash bottle for this purpose to have greater control over the addition process

When required to prepare 250 cm3 of 0.5 mol/dm3 solution of a crystal of Mr 50g

First realize that we need only 250 cm3, not 1 dm3
Now in 250 cm3 there will be: 50/4 = 12.5 g of the solid

So, first add 12.5 g of solid to 50 cm3 of water in a BEAKER ( not the volumetric flask yet). Also note that the volume of water is less than 250 cm3.
Stir properly and if the solid doesn't dissolve add more water until it fully dissolves
Then transfer the solution from the beaker to a volumetric flask. Remember to rinse the beaker with water and transfer the solution to the volumetric flask
Stopper the flask and shake properly
Finally, add the required volume of water to make the solution upto 250 cm3 USE A FUNNEL OR YOU RISK OVERSHOOTING THE MARK

It should be 6.25 grams instead of 12.5 !

 

[salvatore]

I am not really sure about it too but basically if you have to use varying concentrations just keep on adding more water. Like you have 2 mol/dm3 acid and you want to vary its concentration. Do it like this:
Vol of acid 50 40 30 20 10
Corresponding water vol 0 10 20 30 40
Conc 2 1.6 1.2 etc
Just make sure you have the same amount of total vol at each try

Thank you for the reply.
But how did you get the concentrations as 2, 1.6 and 1.2?

 

[SomeStudent]

Thank you for the reply.
But how did you get the concentrations as 2, 1.6 and 1.2?

U r welcome!
Just cross multiply. Conc: Vol of acid
2 50
x 4o

 

[asenfire]

It is said we have 50cm3 of acid of 2 mol/dm3 to react with a certain volume of alkali already present as 250cm3. It is said that
when a titration is carried out the two reacting volumes are approximately equal at the end-point
Now for dilution of the acid what do i do or rather how do i do this
Do i transfer this 50cm3 volume of acid OR another volume?? to a volumetric flask and add water up to the mark??, if so, then what do i do next
OR
Do i use the method of transferring a particular amount of acid to a beaker then adding a particular amount of water to it for dilution. if so then how do i start

Sry if it is confusing, but i just can't understand the mark schemes about dilution, i really need help!!!!!

 

[asenfire]

If this is not enough then can you explain this at least 1c(v)
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_52.pdf

 

[1ajia1]

If this is not enough then can you explain this at least 1c(v)
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_52.pdf

Even I can not do this, I dont understand what they mean by equal volumes? :|

 

[SomeStudent]

Yes, I dont get it either!

 

[SomeStudent]

Also, how do we measure the rate? Mathematically? Say I collected volume of gas collected for the same time interval (what should an ideal interval be?), how will I find out the rate? Vol/Time?

 

[A star]

Even I can not do this, I dont understand what they mean by equal volumes? :|

yar it means the total volume of Hcl and base should be equal at all COSTS

 

[asenfire]

Also, how do we measure the rate? Mathematically? Say I collected volume of gas collected for the same time interval (what should an ideal interval be?), how will I find out the rate? Vol/Time?

Its best if you collect the same volume but in a way that time intervals are different indicating different rates of reaction as time taken to produce that amount of gas is different, in this case rate = 1/t

 

[asenfire]

yar it means the total volume of Hcl and base should be equal at all COSTS

how to do yar?

 

[Khadija.95]

Umm people? I'm a little confused about the scale. So my scale on the x-axis is 0.0006 but I don't think we're supposed to plot that right? Are we supposed to add 0.0006 to each next value on the axis? like 0.0006, 0.0012 and so on? Because that would make plotting very difficult :/

 

[1ajia1]

yar it means the total volume of Hcl and base should be equal at all COSTS

I know that but how will we show in our calculation because say Ca(oh)2 is in burette and hcl is in in pipette. they have different volumes how will we manipulate the concentrations so that equal volumes will be titrated? :O

 

[JAVERIA INAM DANISH]

How do we draw the diagram of may june 2010/52 question 1

 

[SomeStudent]

Its best if you collect the same volume but in a way that time intervals are different indicating different rates of reaction as time taken to produce that amount of gas is different, in this case rate = 1/t

So I measure how much time is taken to collect say 30cm3 of gas? Oh ok, thanks!

 

[1ajia1]

Umm people? I'm a little confused about the scale. So my scale on the x-axis is 0.0006 but I don't think we're supposed to plot that right? Are we supposed to add 0.0006 to each next value on the axis? like 0.0006, 0.0012 and so on? Because that would make plotting very difficult :/

unfortunately chem has weird scales but change it to scientific notation like 6*10^-4 and 12*106-4 so u can easily plot 6 and 12 then write at the end of x axis *10^-4 so examiner will know all ur values in decimals.

 

[A star]

I know that but how will we show in our calculation because say Ca(oh)2 is in burette and hcl is in in pipette. they have different volumes how will we manipulate the concentrations so that equal volumes will be titrated? :O

like for example for 20 cm^3 of CaOH2 you will need 40cm^3 of HCL