Biology; Chemistry; Physics: Post your doubts here!

[zeekay132]

Which of the following pairs of substances reacts to produce the compound shown below?
C2H5CO2C3H7

(a) propene and ethanoic acid
(b) propanol and propanoic acid
(c) ethanol and butanoic acid
(d) ethene and propanoic acid

 

[Saad Mughal]

Which of the following pairs of substances reacts to produce the compound shown below?
C2H5CO2C3H7

(a) propene and ethanoic acid
(b) propanol and propanoic acid
(c) ethanol and butanoic acid
(d) ethene and propanoic acid

(b), propanal (C3H7OH) and propanoic acid (C2H5COOH) will form this ester, propyl propanoate.

 

[Saad Mughal]

what are the experiments to show total internal reflection???

tag me whn u get the answr

I'm not 100% sure about this experiment but,
Equipment: Ray box or Light source, Prism or Semi Circular Glass Block.
-The ray box is placed at an angle to the semi circular glass box, and rays are projected, the light ray is refracted through the glass block.
-The angle of incidence is gradually increased and it is seen that the light rays bend more and more (away from the normal).
-At one point, the angle of incidence refracts the light ray exactly at the surface of the glass block (90 deg.) and this is the critical angle of incidence.
-Beyond this angle of incidence, all the light rays that hit the surface of the glass block are REFLECTED back into the glass block.
-These light rays obey the laws of reflection (angle i = angle r) and thus giving proof for total internal reflection.

 

[TheStallion-Reborn]

(b), propanal (C3H7OH) and propanoic acid (C2H5COOH) will form this ester, propyl propanoate.

and HOW did u figure that out?

 

[Saad Mughal]

and HOW did u figure that out?

C3H7OH + C2H5COOH ----> C2H5COOC3H7 + H2O.
The general reaction b/w alcohols and carboxylic acids,
Alcohol + Carboxylic Acid ----> Ester + Water.

 

[kanchan dhiman]

please send some tips for chemistry, physics,and statistics with notes urgently

 

[Kamihus]

and HOW did u figure that out?

just add H at the end of C2H5CO2 and OH at the end of C3H7
Now look at number of carbon atoms both have three thus propanol and propanoic acid

 

[Muqeet Tahir Malik]

What is the experiment for measuring the effect of temperature on resistenc, how to used in circuit diagrams

 

[usama321]

I'm not 100% sure about this experiment but,
Equipment: Ray box or Light source, Prism or Semi Circular Glass Block.
-The ray box is placed at an angle to the semi circular glass box, and rays are projected, the light ray is refracted through the glass block.
-The angle of incidence is gradually increased and it is seen that the light rays bend more and more (away from the normal).
-At one point, the angle of incidence refracts the light ray exactly at the surface of the glass block (90 deg.) and this is the critical angle of incidence.
-Beyond this angle of incidence, all the light rays that hit the surface of the glass block are REFLECTED back into the glass block.
-These light rays obey the laws of reflection (angle i = angle r) and thus giving proof for total internal reflection.

I was thinking why not first calculate the theoretical critical angle, by calculating the refractive index first by sin i/ sin r. Then get the theoretical critical angle by n = i/sin c. in the end, compare this with the experimental value.

 

[usama321]

and HOW did u figure that out?

Remember, whenever an ester forms, it is formed from a carboxylic acid and an alcohol. now you need to first find out in the ester which one is the acid. We know that all carboxylic acid have COOH in them. Now look at this ester, ethyl ethanoate.

CH3COOC2H5.

Look at the COO in bold, you might have noticed it. It does not contain the usual H at the end like in carboxylic acid. But from this CH3COO, we can of course know that this acid is ethanoic acid, CH3COOH.

Now look after the COO, we see C2H5. We know that esters are also made of alcohols, and now that we know the acid, we can move onto the C2H5. This C2H5 can only be from the alcohol, ethanol, which is C2H5OH. The OH too is missing here in the ester. Now we have identified both the acid and the alcohol.

Lets see what happened to the missing H from acid and the missing OH from the alcohol. They both combined to form H2O, that is water.

If you want to deduce the name of the ester, look at the ester. CH3COOC2H5. When ever we deduce the name of the ester, we first look at the name of the alcohol. The alcohol is ethanol, but in the ester we will call it ethyl. Now look at the acid, it is ethanoic acid, so we will call it ethanoate in the ester. Remember in the name of the ester, the alcohol comes first so ethyl and then the acid ethanoate, the name would be ethyl ethanoate.

 

[usama321]

When drawing a straight line of best fit in physics atp, do we draw a line that has equal number of points above and below it. And how far from one point can the line be? any tips for drawing that line please?

 

[TheStallion-Reborn]

When drawing a straight line of best fit in physics atp, do we draw a line that has equal number of points above and below it. And how far from one point can the line be? any tips for drawing that line please?

tag me when u get the answer

 

[fatima0000]

When drawing a straight line of best fit in physics atp, do we draw a line that has equal number of points above and below it. And how far from one point can the line be? any tips for drawing that line please?

tag me too

 

[usama321]

tag me too

tag me when u get the answer

and only 8 days are left till paper

 

[Saad Mughal]

I was thinking why not first calculate the theoretical critical angle, by calculating the refractive index first by sin i/ sin r. Then get the theoretical critical angle by n = i/sin c. in the end, compare this with the experimental value.

We're asked for an experiment for total internal reflection, I don't quite get how what you say will prove that total internal reflection occurs.

 

[papajohn]

and only 8 days are left till paper

We will all do exactly the same paper at the same time of the day. That interesting

 

[Saad Mughal]

When drawing a straight line of best fit in physics atp, do we draw a line that has equal number of points above and below it. And how far from one point can the line be? any tips for drawing that line please?

tag me when u get the answer

tag me too

You don't have to make bizarre lines or curves for fitting all the points in the graph.
A best fit line means that a straight line with no rugged joints, just a clear smooth straight line.
A best fit curve means that a proper curve that shapes correctly. No weird joints made, for example (a parabolic curve has a U-shape).
There is no exact number of points that are below/above the line. It can be 1 above, 2 below, 2 above, none below, anything!

Tips for drawing graph:
- Use a sharp pencil.
- Clear, smooth curve/straight line with no awkward joints.
- The best fit line mostly consists of 3 points forming the line.
- If say x is proportional to y then the line WILL pass through the origin.
- The data in ATP exams is deliberately given rogue values to show that ERRORS in experiments occur.
- After plotting the graph, verify that you have plotted all the points correctly with proper scaling.
- Use a scale such that your graph covers at least half of the graph page (clear big graph) .
- Do not worry about best fits, there is only one proper line/curve in a given graph, you just have to spot it.
- Lastly, PRACTICE. Practicing these graphs makes you better at making best fit lines/curves and interpreting data.

Hope that helps.

 

[usama321]

We're asked for an experiment for total internal reflection, I don't quite get how what you say will prove that total internal reflection occurs.

oops i mixed up with the critical angle experiment Sorry

 

[Saad Mughal]

oops i mixed up with the critical angle experiment Sorry

Hehe. No problem.

 

[fatima0000]

and only 8 days are left till paper

not 8 but 6