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Date Posted: 05:20:41 11/03/01 Sat
Author: tze may
Subject: q u e s t i o n s
hello mr yeo... so many questions, so little time..
here goes..
1) which one of the following would not show a change in mass when left for several days in an unstoppered bottle?
A: anhydrous calcium chloride
B: polyethene
C: crystalline sodium carbonate
D: ethanol
E: conc. sulphuric acid
i noe it's B but why not C?
2) when carbon dioxide is bubbled for a long time into limewater, a white ppt is formed. the ppt then dissolves to give a clear solution.
white ppt: calcium carbonate.. but how come it dissolves to give a clear solution?? it does? and name the compound formed when the solution turns clear again.
3) did u say that the metals in grp 1 form soluble hydroxides while those in grp 2 form insoluble ones?
4)when lumps of calcium carbonate is added to dilute HCl, a continous stream of bubbles is seen. when lumps of calcium carbonate is added to dilute sulphuric acid, only a few bubbles is seen. Why? is it because when it reacts with sulphuric acid, it produces more things: water, co2, and calcium sulphate izzit?
5)describe carefully how u would prepare a solution of potassium sulphate. by titration method right? right. then they ask how can your method be modified in order to obtain a solution of potassium hydrogen sulphate? what's this?? won't come out for Os right??
6) metals are good reducing agents... right?
7) where is carbon is the reactivity series?
right that's all for now. thanx...
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Re: q u e s t i o n s -- Lim Yee Lian, 00:46:49 11/04/01 Sun
Q2)Carbon Dioxide bubbled into limewater forms white ppt(calcium carbonate). Thus substance reacts with more carbon dioxide to form soluble calcium hydrogencarbonate(soluble in water). That's why colourless solution formed. {PG 415}
[This is out of syllabus]
Q3)Metals in Gp1 formed soluble hydroxide.(Sodium hydoxide,potassium hydoxide)Whereas Gp2 metals they form hydroxides which are slightly soluble only if not are insoluble.(calcium hydroxide-limewater(slightly soluble,magnesium hydroxide is insoluble)
Q6)Metals are reducing agents-only in displacement reactions with less reactive metals.Metals which are more reactive will displace the ions of less reactive metals in the reactivity series,from solutions.(PG 192)
Q7)Only metals are classified in the reactivity series.As for carbon, carbon is a non-metal.Carbon is a rducing agent as well... It can take oygen away from oxides of metals that are not high up in the reacttivity series.(middle of the reactivity series.eg:zinc,copper,iron etc)[PG 194]
Q5)Potassium sulphate is a soluble salt...That's why it can prepared by titration method....Potassium hydrogen sulphate is also a salt formed by reacting sulphric acid and potassim hyroxide.
H2SO4+2KOH ---K2SO4+H2O
(potassium sulphate)
It can also formed another substance.
H2SO4+KOH ----KHSO4+H2O
I don't know how to modify the experiment to get the product.(SORRY)
Q4)Calcium sulphate is an insoluble salt. When calcium carbonate reacts with Hydrocloric acid,the substances are calcium chloride(soluble salt) ,water and carbon dioxide...
But I don't know why are there more bubbles(SORRY)
Q1)I dun know as well....
Hope my answers can be of little help to u!!:)
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k2so4 Crystallisation -- asanda, 08:00:33 04/10/05 Sun
how do your go about writing a (LAab)report on K2SO4 crystallision
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Re: k2so4 Crystallisation -- asanda, 08:01:52 04/10/05 Sun
>how do your go about writing a (LAab)report on K2SO4
>crystallision
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Re: q u e s t i o n s -- Mr. Yeo Woei Ter, 16:51:40 11/05/01 Mon
Ok, here's the answer:
1) Washing soda is sodium carbonate decahydrate Na2CO3.10H2O, large translucent crystals.
On exposure to air, the crystals loss mass and become coated with a fine powder which render them opaque. Each molecule of washing soda has given up to the atmosphere 9 molecules of water of crystallisation.
Na2CO3.10H2O(s) ---> Na2CO3.H2O(s) + 9H2O(g)
2) Yee Lian is correct for this question. The equations are in your "*textbook!", try to search for it.
3) Yee Lian is correct, note that Barium hydroxide is also soluble.
4) I think I have already replied to this question. Calcium sulphate formed in the second reaction is only slightly soluble. So it will form a layer on the surface of the carbonate and prevent it from further reaction with the acid.
5)The equations for the reactions are:
2KOH + H2SO4 ---> K2SO4 + 2H2O
KOH + H2SO4 ---> KHSO4 + H2O
From the equations above, it is evident that the amount of potassium hydroxide needed to convert a given amount of sulphuric acid into potassium hydrogencarbonate is half that required to convert it to potassium carbonate.
Firstly, measure say, 25cm3 of 1 mol/dm3 potassium hydroxide solution into a titration flask, add indicator and then run carefully, from a burette, 1 mol/dm3 dilute sulphuric acid, until the end point is reached. Note the volume of dilute sulphuric acid needed (say x cm3). The solution contains potassium sulphate.
Then, measure out 25cm3 of the same potassium hydroxide solution and add to it from the burette, 2x cm3 of the same acid. This solution now contains potassium hydrogensulphate.
(Then you must describe how to obtain the crystals from the solution by the usual way)
6) Yes, the more reactive the metal, the stronger its reducing property.
7) Yee Lian is right.
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