Question

Can anyone explain me how to do this?

Answer 1

The prediction is Solubility of potassium nitrate increases with the temperature of the solution.

Answer 2

http://screencast.com/t/LrwJqlTDI

Answer 3

@ParthKohli @Vincent-Lyon.Fr

Answer 4

@emcrazy14

Answer 5

@chmvijay

Answer 6

Okay, so here's the way I'd do it:
1. Take 5 test tubes and label them. Add 2.0g, 4.0g, 6.0g, 8.0g and 10.0g of potassium nitrate (measure with an electronic balance) to each test tube respectively.
2. Add exactly 5.0 cm^3 of water to each test tube. (measure with a measuring cylinder)
3. Set up a water bath (the test tube inside a beaker filled with tap water) and heat it (with a bunsen flame) until the temperature is about 90 degree Celsius.
4. Stir the potassium nitrate with the stirrer until it is completely dissolved.
5. Remove the test tube from the water bath and put in a warm thermometer. Hold the test tube upto light and record the temperature at the instant when crystallization starts.
6. Repeat for each of the test tubes and record the data.

Answer 7

Edit: I didn't see they mentioned the 'boiling tube'. You can write boiling tube instead of test tube.

Answer 8

Instead of changing the mass of potassium nitrate, why cant we add different volumes of water using a burette keeping the mass of KNo3 constant, coz either way the solubility changes

Answer 9

It's up to you. I mentioned that's the way I'd do it.
If you change the volume of water, then you can heat up the boiling tube and record the temperature at which the potassium nitrate fully dissolves.

Answer 10

why not the temperature at which the crystallisation occurs?

Answer 11

Yes, you could do it that way too.

Answer 12

and for the amounts of water and potassium nitrate we should mention values?

Answer 13

Yes, you can write any value (keeping in mind that it doesn't exceed the capacity of the apparatus used). Like a typical boiling tube can hold around 30 cm^3 of water. So writing add 50cm^3 of water to dissolve the potassium nitrate would be wrong and lose you marks.

Answer 14

oh ok thanks :)

Answer 15

This is how the apparatus would look like for the question you asked.

Answer 16

oh now everythings fine how do i determine the different mass i could use for the experiment

Answer 17

They give the solubility of ammonium nitrate as 2.5mol/100g. So how much mass of ammonium nitrate can be dissolved in 100 cm^3 of water?

Answer 18

2.5* ( Mr(Ammonium nitrate))

Answer 19

Yes. So now you can calculate the maximum mass of NH4NO3 which can dissolve in 100 cm^3 of water. You can select the other masses smaller than this value.

Answer 20

that would give different concentrations, which give different temperature rise, and u can find the relationship?

Answer 21

Yes, exactly.

Answer 22

and how do i determine the volume of water i would use, i mean for other experiments as well

Answer 23

You can keep the volume constant. The maximum capacity for a styrofoam cup is 200 cm^3 (I think), so you can add 100 cm^3 of water in order to prevent spraying out of the mixture. Now as you change the masses of NH4NO3, the concentration will still change.

Answer 24

oh okay thanks :) So hows ur prep goin

Answer 25

Don't know. A2 is quite hard. >_<

Answer 26

haha and u wil end up with 5 or 6A * at the end :D

Answer 27

anyways hve u come across any hard questions?

Answer 28

Hahaha, I just got 4 subjects this time. xP Yes, quite a lot of them.

Answer 29

hve u had them posted on open study ?