Chemistry practical 34 oct/nov important

[adhirajshinde]

The last answer which we had to smell was ester rite?

 

[soccerprinc3]

The last answer which we had to smell was ester rite?

Carboxylic acid

 

[shikha95]

The last answer which we had to smell was ester rite?

The compound formed was an ester, but the powder was a carboxylic acid

 

[Ansar Khan]

Guys, please tell what readings were you getting (in seconds) for the blue/black colour to appear. This is very important because in June 2003 paper, six marks were allocated only for the accuracy of readings.

 

[Ansar Khan]

Secondly, there was a question asking that what will be the effect on the reaction time if the concentration of sodium thiosulfate used is 0.25 (instead of 0.50)?

 

[soccerprinc3]

Guys, please tell what readings were you getting (in seconds) for the blue/black colour to appear. This is very important because in June 2003 paper, six marks were allocated only for the accuracy of readings.

Um i got 10,13,17,26 and 52 ...what about you?

 

[Ansar Khan]

Um i got 10,13,17,26 and 52 ...what about you?

I got very similar readings to you, but I assumed the last one as I was out of time. My fifth reading was in the early 30s. What do u think how many marks will I get on the table? And what about the question that asked about the effect on the reaction time if the concentration of sodium thiosulfate is reduced from 0.5 to 0.25?

 

[Ansar Khan]

Guys the question in which we were supposed to calculate the mean, were the units in cm^3? I remember that I was getting 3.56.

 

[Ansar Khan]

it turned blue litmus paper red.

If blue litmus turned red, then was it chlorine gas?

 

[Z.S.M]

If blue litmus turned red, then was it chlorine gas?

no. cl 'bleaches' litmus paper

 

[Z.S.M]

Secondly, there was a question asking that what will be the effect on the reaction time if the concentration of sodium thiosulfate used is 0.25 (instead of 0.50)?

the reaction time would obviously increase. as rate is directly proprtional to concentration.

 

[Z.S.M]

Guys the question in which we were supposed to calculate the mean, were the units in cm^3? I remember that I was getting 3.56.

it was 56.2.............. i think

 

[Saloon]

the reaction time would obviously increase. as rate is directly proprtional to concentration.

I was just about to write this then the time was up and the invidulator was standing next to me, waiting for me to give her my paper ... Do you remember how many marks that was for? Feel bad leaving such an easy question out

 

[AAAAAA]

you don't consider 'outliers' in chem. it's not exactly a statistics paper. and besides, it was just a one mark question. which means you don't have to be a stats genius to answer it. your calculator had to do all the work!

The question asked to calculate an appropriate mean, not just a mean. I think that outliers should therefore be considered.

 

[Ansar Khan]

no. cl 'bleaches' litmus paper

According to some books, chlorine turns litmus red first, then bleaches it. It could not be CO2 or SO2 because you don't need to heat the solution to identify these gases. For CO2 u needed to use limewater and dichromate for SO2. But the question asked to test with litmus, and I guess chlorine would be the only gas that'll turn it red.

 

[Ansar Khan]

no. cl 'bleaches' litmus paper

And Zahra as far as I remember, we were asked to add dilute HCl first and then heat the solution. It's obvious that the gas evolved would be chlorine. What did u write btw?

 

[Z.S.M]

And Zahra as far as I remember, we were asked to add dilute HCl first and then heat the solution. It's obvious that the gas evolved would be chlorine. What did u write btw?

we were only asked for the observation

 

[Z.S.M]

According to some books, chlorine turns litmus red first, then bleaches it. It could not be CO2 or SO2 because you don't need to heat the solution to identify these gases. For CO2 u needed to use limewater and dichromate for SO2. But the question asked to test with litmus, and I guess chlorine would be the only gas that'll turn it red.

according to the qualitative analysis notes from CIE itself, Cl bleaches litmus.

 

[Z.S.M]

In the mar
In the mark scheme, the exact word written is "per second"..... But no where is written S^-1. The difference between bot of them is that, the unit would still be per second if you multiply a constant. ( like you said constant does not have any unit)
but at the end you do have to give constant because it might change the magnitude or the uni itself. Like, the constant 100 can change the unit of cm into M if you divide the constant. So, in order to know the magnitude and what is the exact unit, Constant is necessary.

Look. The 10^3 is not in the units. I’ll give you an example. Suppose your time is 10 seconds. You do 1000/10 and get 100 for the rate column. But you write it as 0.1 x 10^3. And all the subsequent values like that too. You put the 10^3 in the heading so you don’t have to write it again and again, the same as you do with units. In the 2003 paper, the examiners required the student to divide 1 by the time and put the 10^3 in the heading to represent the 1000 in the numerator of every value of rate. Hope you understand now.

 

[Ansar Khan]

we were only asked for the observation

I know we weren't supposed to write the deduction, but I wrote it anyways. See it can't be CO2 or SO2 cuz these gases don't require any heating. Guess the only one left is chlorine. Will they cut my mark on that? I wrote the observation also though.