Chemo P5 tips

[hanzlabia]

hey zeebuiha thnks you are a great help, i want to ask ke aik question mai agar dilution karni ho or sirf concentration btai ho to kya diluted solutions ka volume same rkna ho ga, or plz her aparatus ka standard volume bta do

 

[zeebujha]

hey zeebuiha thnks you are a great help, i want to ask ke aik question mai agar dilution karni ho or sirf concentration btai ho to kya diluted solutions ka volume same rkna ho ga, or plz her aparatus ka standard volume bta do

Suppose you are given a solution with concentration 1.0 mol/dm3 and you have to serially dilute it to various concentrations then:

Volume of solution / cm3 Volume of water/cm3 Relative concentration

50 0 1.0
40 10 0.8
30 20
20 30
10 40
5 45

I have kept the volume constant at 50 cm3 but this is not necessary. All you need to do is get the right concn using the volume of water and volume of solution. Try filling the other relative concentrations yourself.

 

[blueindigo]

hey thanks!! they're of great help!!!!

 

[hanzlabia]

thnks or aparatus ka standard volume?

 

[ammarelahi]

one question..when calculating standard enthalpy change of neutralisation per mole, the expression for heat energy mc(delta)T should be divided by the moles of acid or moles of alkali ??

 

[RafaySid]

Plz answer the previous question and this one too.
As enthalpy change = mcΔT
But is using Q=vcΔT right, where 'v' is the volume of the liquid? What's the logic behind this? Is it the volumetric heat capacity??

 

[WellWIshER]

the way i think abt it is...tht da heat lost by wtevea substance is da heat gained by water.

so we use water;s mass

ans to da former question.....
if u have acid in ur burette then take da moles of acid..i think dis is da ans

 

[zeebujha]

thnks or aparatus ka standard volume?

If it is a simple dilution, you could use a 250 cm3 beaker. We are measuring the real deal using burette or the pipette. However, if you want to mix the solution really well, you could use the graduated flask. I think I will just stick with the 250cm3 beaker for now.

 

[zeebujha]

one question..when calculating standard enthalpy change of neutralisation per mole, the expression for heat energy mc(delta)T should be divided by the moles of acid or moles of alkali ??

If you are using an excess of alkali then the expression has to divided by the number of moles of acids

 

[zeebujha]

Plz answer the previous question and this one too.
As enthalpy change = mcΔT
But is using Q=vcΔT right, where 'v' is the volume of the liquid? What's the logic behind this? Is it the volumetric heat capacity??

the thing is in our practical, most solutions primarily consist of water and the density of water is 1g/cm3. So, 1 cm3 corresponds to 1 gram. Thus for any solution, you could either use its mass or its volume, the numerical value will be the same. However, it is technically correct to use the mass of the solution rather than its volume

 

[abrraza]

hey.. can any 1 explain plzz... how to find con. of acid in oct nov10 q2 a .. 53

 

[borntofly]

Titration is accurate because:
1. Standard solution of acid/base is used
2. we obtain concordant titres
3. % error in pipette and burette is very small
4. The end point of a titration is sharp

hey what does STANDARD SOLUTION of acid and base mean? Does it mean 1.0 mol/dm3 of acid or base in 25°C temperature?

 

[zeebujha]

Titration is accurate because:
1. Standard solution of acid/base is used
2. we obtain concordant titres
3. % error in pipette and burette is very small
4. The end point of a titration is sharp

hey what does STANDARD SOLUTION of acid and base mean? Does it mean 1.0 mol/dm3 of acid or base in 25°C temperature?

In analytical chemistry, a standard solution is a solution containing a precisely known concentration of an element or a substance. It is prepared using a standard substance, such as a primary standard. Standard solutions are used to determine the concentrations of other substances, such as solutions in titrations. The concentrations of standard solutions are normally expressed in units of moles per litre (mol/L, often abbreviated to M for molarity), moles per cubic decimetre (mol/dm3), kilomoles per cubic metre (kmol/m3) or in terms related to those used in particular titrations (such as titers).
A simple standard is obtained by the dilution of a single element or a substance in a soluble solvent with which it reacts.

 

[borntofly]

Is it always necessary to include ORIGIN (0,0) in our graph ?

 

[abrraza]

Is it always necessary to include ORIGIN (0,0) in our graph ?

no... it depends

 

[abrraza]

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

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

in A.. parent solution is 2mol/dm3 ... if we take 125cm3 of parent solution in flask marked at 250cm3... and top off with water.. ?? instead of taking 100 because this wont give us 1.0mol/dm3 .. confused :S

 

[borntofly]

C1V1 = C2V2

2 x 125 = C2 x 250 so, C2 = 1.0 mol/dm3

isn't this the process?

 

[abrraza]

If you want to flush oxygen out of a system, use an inert gas that doesn't oxidise . Very useful when we are conducting a reduction experiment of metal oxides

explain this plzzzz

 

[zeebujha]

C1V1 = C2V2

2 x 125 = C2 x 250 so, C2 = 1.0 mol/dm3

isn't this the process?

sorry, you have to take 125 cm3 of the parent solution! you are absolutely correct and great spotting

 

[zeebujha]

If you want to flush oxygen out of a system, use an inert gas that doesn't oxidise . Very useful when we are conducting a reduction experiment of metal oxides

explain this plzzzz

suppose you had to reduce CuO. You would have to heat the solid in a container with H2 gas. But we already have some air (which contains oxygen) present in the container initially. So, the reduced Cu will keep on getting oxidised until all of the O2 in the container has not reacted and this will mean you will have to use greater volume of Hydrogen to reduce a given mass of Cuo due to re-reduction of the oxidised Cu.
So, it would be best if you could flush O2 out of the apparatus on the first place. If you pass a stream of H2 into the container, the volume of H2 will eventually displace all of O2. So, there will be no O2 in the system to re-oxidise Cu.