Chem P5 most common planning questions and topics

[beacon_of_light]

Wow.... tats a lot. paper 5 is a few days ahead and surely need helps in this question! hellpp me guys!!! before its too late!

Hey guys! I m still not sure about paper 5 chemistry, for example a question from Nov10/53 question 1

Using the apparatus shown in (c) design a laboratory experiment to test your prediction
in (a). In addition to the standard apparatus present in a laboratory you are provided with the
following materials.

• 2.00 mol dm–3 aqueous hydrogen peroxide
• a supply of manganese(IV) oxide
(i) Complete the table below to show how you would prepare five solutions of aqueous
hydrogen peroxide. Make sure that the correct units are recorded.
expt No. volume of H2 O2 volume of H2O concentration of H2O2
1
2
3
4
5

Note That: I just dont understand where to get all the amounts to fill in to the table!

you need to assume your own values but remember to keep the total volume constant... for dilution use the formula c1v1=c2v2

 

[diwash]

i think zahraahmed means anamolous points...i often see the experimental procedures and see the dependent variable for the anamolous ponits..I dont know if this is the correct way but most of the time this method works

 

[borntofly]

can anyone tell me how to explain the anamolies........................

what anamolies do u exactly mean??

For the anomalous points, you should look at the quantities on the y-axis as it is the DEPENDENT variable. The anomalous point is usually due to the error that occurs while measuring the dependent variable. So explain the error that might occur while measuring the dependent variable.

 

[zeebujha]

guys, can you please explain what a divided flask is??

 

[borntofly]

guys, can you please explain what a divided flask is??

The use of divided flask comes in when you have to determine the rate of reaction in which gas evolves and you have to measure the volume of gas evolved using a gas syringe.

Usually a divided flask is a test-tube kept inside a conical flask. One of the reagents is kept in the test-tube and the other is kept in the conical flask to prevent the reaction from taking place till your apparatus is gas tight. Then you invert the conical flask to mix the reactants.

A divided flask (test-tube) is used to ensure that the reaction does not start until all the apparatus is assembled and gas tight so that the gas evolved does not get lost. It basically works by keeping the two reagents separated from each other until you are ready to begin. To start, the flask is shaken, causing the reactants to come into contact and setting off the reaction.

I found a picture but i'm not sure it is the correct one. Just to make yourself familiar you can take a look at this picture:
http://www.rpdp.net/sciencetips_v3/imag ... age006.jpg

and this one is also a divided flask
http://www.lisgar.net/magwood/mass%20flask.gif

hope this helps.

 

[WellWIshER]

guys oct nov 09 51 q2 how do we find moles?????

wts da ratio!!

 

[borntofly]

Guys lets explain the best procedure for each of these, we can also clear any confusions that might appear:

1. Enthalpy Changes (sometimes using Hess's Law)
2. Determination of Solubility
3. Determination of rates of reaction
4. Water of Crystallization (percentage of water lost)
5. Percentage by mass of some elements or compounds in other compounds
6. Elemental Analysis
7. Ion Tests (Qualitative Analysis Notes given)
8. Compostion of given solutions
9. Redox (Electrolysis)
10. Electrophoresis
11. Calculating pH, pka, pkb and ksp.

 

[angel eyez]

guys c this qs plz
n/09 52 qs # 1) f)
in the marking scheme they have divided by the ACID moles...
why have they done this.....n y haven't they divide it by NAOH MOLES??

PLZ HELP PEOPLE N FAST....
M UNABLE TO PREPARE 4 MY CHEM P5

 

[WellWIshER]

guys oct nov 09 51 q2 how do we find moles?????

wts da ratio!!

anyone????

1 more q guys how to make a graph of june 09 q2

its impossible!!

 

[beacon_of_light]

guys oct nov 09 51 q2 how do we find moles?????

wts da ratio!!

anyone????

1 more q guys how to make a graph of june 09 q2

its impossible!!

You'll get a graph like this after plotting the points and drawing two different curves...
The point where the two curves intersect is the transition temperature (to be read from the x-axis)

 

[beacon_of_light]

guys oct nov 09 51 q2 how do we find moles?????

wts da ratio!!

In the table of results, you've already calculated the mass of zinc and iodine used...
Now divide these masses by their respective atomic masses to obtain moles...
Then find the ratio of iodine to zinc ...

 

[borntofly]

Investigating how the rate of reaction depends on the concentration of hydrochloric acid.

Given: magnesium ribbon
2 mol/dm3 hydrochloric acid

>Apparatus required:

1. Divided Conical flask, 250 cm3 (or a test-tube inside the flask)
2. Rubber Bung
3. Delivery tube
4. Gas Syringe, 50 cm3
5. Goggles
6. Stopwatch or timer
7. Measuring cylinder, 50 cm3
9. Beaker, 250 cm3

>Procedure:


i) Measuring the independent variable:

1. Dilute the HCl adding different volumes of 2 mol/dm3 acid to different volumes of water using a measuring cylinder
2. Prepare at least 5 dilute solutions of HCl with different concentrations.
3. Calculate the concentration of HCl by using the formul C1V1 = C2V2

For example:

HCl//cm3.................Water/cm3.........Conc./mol/dm3

10.............................40......................0.4
20.............................30......................0.8
30.............................20 .....................1.2
40.............................10......................1.6
50............................. 0......................2.0

ii) Mixing reactants without loss of gas

Use a divided flask with magnesium ribbon and acid in different sections. Mix them by shaking after the apparatus is airtight.

iii) Measurement of dependent variable

Use a stopwatch to measure the volume of gas evolved in a fixed interval of time for every experiment carried. Record the data to plot a graph

iv) Control of other variables

Perform the experiment in room temperature. OR keep the volume of HCl constant OR keep the surface area or length of magnesium ribbon constant

v) Range of concentration used

0.4 to 2.0

Table for data collection

HCl//cm3...............Water/cm3 .......Conc./mol/dm3....... time/s ...... Volume of H2/cm3

10............................40..................0.4 .................. 20
20............................30................. 0.8 .................. 20
30............................20..................1.2.................. 20
40............................10..................1.6 .................. 20
50............................ 0 ..................2.0 .................. 20

I hope this will be useful, please can you guys give solutions for some others. Let's help eachother.

 

[beacon_of_light]

Thanks that really helped!
but I think a divided flask isn't the one you drew...it has a constriction in b/w to prevent the mixing of reagents until you start the experiment by shaking the flask!

 

[diwash]

Cant we draw a wolf's bottle and thristle funnel..insted of divided conical flask?

 

[Xam]

Investigating how the rate of reaction depends on the concentration of hydrochloric acid.

Given: magnesium ribbon
2 mol/dm3 hydrochloric acid

>Apparatus required:

1. Divided Conical flask, 250 cm3 (or a test-tube inside the flask)
2. Rubber Bung
3. Delivery tube
4. Gas Syringe, 50 cm3
5. Goggles
6. Stopwatch or timer
7. Measuring cylinder, 50 cm3
9. Beaker, 250 cm3

>Procedure:


i) Measuring the independent variable:

1. Dilute the HCl adding different volumes of 2 mol/dm3 acid to different volumes of water using a measuring cylinder
2. Prepare at least 5 dilute solutions of HCl with different concentrations.
3. Calculate the concentration of HCl by using the formul C1V1 = C2V2

For example:

HCl//cm3.................Water/cm3.........Conc./mol/dm3

10.............................40......................0.4
20.............................30......................0.8
30.............................20 .....................1.2
40.............................10......................1.6
50............................. 0......................2.0

ii) Mixing reactants without loss of gas

Use a divided flask with magnesium ribbon and acid in different sections. Mix them by shaking after the apparatus is airtight.

iii) Measurement of dependent variable

Use a stopwatch to measure the volume of gas evolved in a fixed interval of time for every experiment carried. Record the data to plot a graph

iv) Control of other variables

Perform the experiment in room temperature. OR keep the volume of HCl constant OR keep the surface area or length of magnesium ribbon constant

v) Range of concentration used

0.4 to 2.0

Table for data collection

HCl//cm3...............Water/cm3 .......Conc./mol/dm3....... time/s ...... Volume of H2/cm3

10............................40..................0.4 .................. 20
20............................30................. 0.8 .................. 20
30............................20..................1.2.................. 20
40............................10..................1.6 .................. 20
50............................ 0 ..................2.0 .................. 20

I hope this will be useful, please can you guys give solutions for some others. Let's help eachother.

How did u do that?

HCl//cm3.................Water/cm3.........Conc./mol/dm3

10.............................40......................0.4
20.............................30......................0.8
30.............................20 .....................1.2
40.............................10......................1.6
50............................. 0......................2.0

 

[borntofly]

C1V1 = C2V2

so C2 = C1V1/V2

 

[Xam]

plz can u explain w.r.t data?

 

[borntofly]

What is the formula to calculate the solubility ?

Given, mass of saturated solution
mass of crystals

 

[nealDSA]

C'Mon People .. Lets Help Each Other Out And PLS PLS Post The Planning Procedure For All Those P5 Topics =D !!

 

[WellWIshER]

guys oct nov 09 51 q2 how do we find moles?????

wts da ratio!!

In the table of results, you've already calculated the mass of zinc and iodine used...
Now divide these masses by their respective atomic masses to obtain moles...
Then find the ratio of iodine to zinc ...

y is da ratio IODINE TO ZINC AND NOT ZINC TO IODINE????