Biology; Chemistry; Physics: Post your doubts here!

[Saad Mughal]

Can anyone help me with part (f) and (g)?
P.S. The picture quality is poor, uploaded in a hurry.
If you can't read them then just see the diagram,
The parts are,
(f) The man now walks past A towards the left-hand of the plank. What is the upward force from the trestle at B at the instant the plank starts to tip?
(g) How far is the man from A as the plank tips?
I need explanations for both parts please.

 

[TheStallion-Reborn]

cannsum1 pleeeeaase help me with question number 9 part g&h of chemistry may/jume2006 paper 4. sorrybfor inconvinience, i can't post the link here since im using my phone. thamkyou

 

[Saad Mughal]

cannsum1 pleeeeaase help me with question number 9 part g&h of chemistry may/jume2006 paper 4. sorrybfor inconvinience, i can't post the link here since im using my phone. thamkyou

In part (e), we deduced the fact that 25.7 cm^3 of volume is used to titrate a 25 cm^3 sample of T, right?
Through the 25.7 cm^3, we calculated the no. of moles. of potassium manganate (VII) in (f) by using the No. of moles = Concentration * Volume formula; the number of moles of POTASSIUM MANGANATE (VII) in the 25 cm^3 of T was hence 0.000514 moles.

In part (g), they stated that,
1 mol. of potassium manganate(VII) reacts with 5 mol. of iron (II) sulphate,
Therefore, the ratio is 1:5.
Using this ratio,
No. of moles of iron = 0.000514 * 5 = 0.00257 moles in the 25 cm^3 solution of T.

In part (h),
The volume of T is 10 times then that in part (g), i.e. (250 cm^3),
The amount of volume of S that reacts with T is in the ratio 25.7:25 (the volume - volume ratio remains the same)
Hence,
For 250 cm^3 of T, (25.7 * 10) = 257 cm^3 of S would be needed.
For 257 cm^3 of S, Moles of Potassium Manganate (VII)= (0.02)(257/1000) = 0.00514
Hence, using the mole - mole ratio (1:5) of potassium manganate(VII) and iron (II) sulphate,
Moles of Iron (II) Sulphate = 0.00514*5 = 0.0257.
(You can also directly multiply the answer in g by 10 since I was giving an explanation as to how that works).
Hope that helps

 

[usama321]

Can anyone help me with part (f) and (g)?
P.S. The picture quality is poor, uploaded in a hurry.
If you can't read them then just see the diagram,
The parts are,
(f) The man now walks past A towards the left-hand of the plank. What is the upward force from the trestle at B at the instant the plank starts to tip?
(g) How far is the man from A as the plank tips?
I need explanations for both parts please.

well i am not sure about the f part but here is what comes into my mind about part g

Taking plank A as pivot. The clockwise moment would be 2*120 = 240Nm (due to the weight). By the way the picture is not clear about the weight of the man, am taking it as 480. Now,

480*x = 240
x = 0.5m

so at o.5m the forces are at equilibrium. So, it should be more than 0.5m, perhaps 0.51 or 0.6?

 

[Saad Mughal]

well i am not sure about the f part but here is what comes into my mind about part g

Taking plank A as pivot. The clockwise moment would be 2*120 = 240Nm (due to the weight). By the way the picture is not clear about the weight of the man, am taking it as 480. Now,

480*x = 240
x = 0.5m

so at o.5m the forces are at equilibrium. So, it should be more than 0.5m, perhaps 0.51 or 0.6?

I made the same calculations and assumed it to be 0.6 m. However, the answer is 0.5 m.

 

[usama321]

I made the same calculations and assumed it to be 0.6 m. However, the answer is 0.5 m.

is the weight 480N?

 

[Saad Mughal]

Yes.
Well, thanks for trying.

 

[Usama Jawad]

Can anybody help me with these chem questions,They are not from pastpapers
Question 1:-Describe what is seen when aqueous ammonia is added drop by drop to Zinc Sulphate solution until present in excess.Give the ionic equation for the reaction?[1]
Question 2:-How to make Copper(II)Carbonate from Copper(II)Sulphate?Observations and Chemical and Ionic Equation?[2]
Question 3:-How to obtain Copper from Copper(II)Sulphate?Observations and Chemical Reaction[3]
Question 4:-Give experimental details of how Aluminium can be used in a thermite reaction to obtain a named metal(iron) from its ore Fe2O3.Describe any other observations you would expect to make and write an equation for the reaction?[2]
Please help

 

[A star]

no offence but aall questions cept 4 basic :/
Q1 this is a test for zinc ion and you can see it from test of cations that white ppt dis in excess
Q2 mix Na2CO3 woth CuSO4 . you will find a ppt of CuCO3 filter and wash then dry
Q3 electrolysis of aques copper sulphate ( redish brown copper deposits blue solution decolourises
Q4 since almunium is higher in reactivity series it can displace Fe from its diff salts and oxides

 

[Usama Jawad]

no offence but aall questions cept 4 basic :/
Q1 this is a test for zinc ion and you can see it from test of cations that white ppt dis in excess
Q2 mix Na2CO3 woth CuSO4 . you will find a ppt of CuCO3 filter and wash then dry
Q3 electrolysis of aques copper sulphate ( redish brown copper deposits blue solution decolourises
Q4 since almunium is higher in reactivity series it can displace Fe from its diff salts and oxides

thnx but I forgot to mention a clause in question 3 so you will have to think of it again
You have to use any method but electrolysis
and can you tell me ionic equation for Q 1 (i already knew that it was a cation test )

 

[usama321]

q1 : When aqueous ammonia is dropped, a white precipitate will form, which would dissolve in excess of aqueous ammonia. Zn2+ + 2OH- = Zn(OH)2

q2 : copper carbonate is an insoluble salt. So, we will use precipitation method. Add aqueos Na(CO3)2 to aqueous Copper sulphate. A precipitate of CuCO3 will form (dont know the colour). Filter it, wash, and dry. (I am not sure about the equation here)

q3: Add a more reactive metal to the solution e-g Magnesium. It would displace the Cu, which would settle down at the bottom (reddish brown color). Also, there might be some bubbles produced (read it in a mark scheme). Filter the copper.
CuSO4 + Mg = MgSO4 + Cu

q4: I am not sure about this one. Make a mixture of powdered Al and Fe2O3. When provided enough heat, e-g ignited, the reaction would start. Al being more reactive will displace Fe from its compound. the reaction would be exothermic so a large ammount of heat will be produced. Example is it is used in welding. The equation would be 2Al + Fe2O3 = Al2O3 + 2Fe

Someone do correct me if i am wrong somewhere

 

[Usama Jawad]

q1 : When aqueous ammonia is dropped, a white precipitate will form, which would dissolve in excess of aqueous ammonia. Zn2+ + 2OH- = Zn(OH)2

q2 : copper carbonate is an insoluble salt. So, we will use precipitation method. Add aqueos Na(CO3)2 to aqueous Copper sulphate. A precipitate of CuCO3 will form (dont know the colour). Filter it, wash, and dry. (I am not sure about the equation here)

q3: Add a more reactive metal to the solution e-g Magnesium. It would displace the Cu, which would settle down at the bottom (reddish brown color). Also, there might be some bubbles produced (read it in a mark scheme). Filter the copper.
CuSO4 + Mg = MgSO4 + Cu

q4: I am not sure about this one. Make a mixture of powdered Al and Fe2O3. When provided enough heat, e-g ignited, the reaction would start. Al being more reactive will displace Fe from its compound. the reaction would be exothermic so a large ammount of heat will be produced. Example is it is used in welding. The equation would be 2Al + Fe2O3 = Al2O3 + 2Fe

Someone do correct me if i am wrong somewhere

thanx a lot

 

[TheStallion-Reborn]

no offence but aall questions cept 4 basic :/
Q1 this is a test for zinc ion and you can see it from test of cations that white ppt dis in excess
Q2 mix Na2CO3 woth CuSO4 . you will find a ppt of CuCO3 filter and wash then dry
Q3 electrolysis of aques copper sulphate ( redish brown copper deposits blue solution decolourises
Q4 since almunium is higher in reactivity series it can displace Fe from its diff salts and oxides

i undrr stood all of it but just aa few ambiguities. if v add sodium to copper sulphate v will ofc se copper deposits and sodium sulphate will be formed but will addition of sodium CARBONATE mean that copper will joim with the carbonate. any theory or conceot which may explain this? and for the last part i got the concept but if u could please give the answr in a prper form@ cx i dont get hw to answr the question

 

[TheStallion-Reborn]

Well, here actually Na displaces Cu from its sulphate. Its not the other way around.

i noe thrt. thts gna b always the case because sodium is more reactive than copper. read my post again :/

 

[usama321]

i noe thrt. thts gna b always the case because sodium is more reactive than copper. read my post again :/

which question are you talking about?

 

[A star]

i undrr stood all of it but just aa few ambiguities. if v add sodium to copper sulphate v will ofc se copper deposits and sodium sulphate will be formed but will addition of sodium CARBONATE mean that copper will joim with the carbonate. any theory or conceot which may explain this? and for the last part i got the concept but if u could please give the answr in a prper form@ cx i dont get hw to answr the question

ok no problem usama321 stated as precisely as possibly can but ill fibe you a little more detail
its basically a double disp reaction . sodiumcarbonate which is soluble is reacting with cupper sulphate also soluble the anions will be exchange and sodium sulphate will remain as a colourless solution while coppercarbonate precipitates out which can be filtered. sodium is displacing copper not copper sodium OK. and make sure that for this kind of answer that ALLthe reactants are soluble and ONLY and ONLY one product is insoluble for a precipitate. hope i am clear .

 

[A star]

i noe thrt. thts gna b always the case because sodium is more reactive than copper. read my post again :/

as to apaper answering form try using this equation
Na2CO3(aq) + CuSO4 (aq) = Na2SO4(aq) + CuCO3(ppt)
blue solutionn declourises and a ppt is formed hope this helps

 

[TheStallion-Reborn]

ok no problem usama321 stated as precisely as possibly can but ill fibe you a little more detail
its basically a double disp reaction . sodiumcarbonate which is soluble is reacting with cupper sulphate also soluble the anions will be exchange and sodium sulphate will remain as a colourless solution while coppercarbonate precipitates out which can be filtered. sodium is displacing copper not copper sodium OK. and make sure that for this kind of answer that ALLthe reactants are soluble and ONLY and ONLY one product is insoluble for a precipitate. hope i am clear .

thankies. i was cnfusd abt the doubl displacmnt. i knew tht sodium will displace copper bt didnt knw hw will carbonate replace sulphate r mayb the other way. infct m still nt clear.

 

[A star]

thankies. i was cnfusd abt the doubl displacmnt. i knew tht sodium will displace copper bt didnt knw hw will carbonate replace sulphate r mayb the other way. infct m still nt clear.

why will it do it is not i your couse infact not even in mine xD just know that half things u are learning will become loads clearer n A levels

 

[nidz]

Can someone ans this question? It's from june 2012 p22
Copper(II) chloride can be prepared by the reaction between copper(II) carbonate and
hydrochloric acid.
(i) Construct the ionic equation for this reaction.

Since copper carbonate is insoluble it should not be written in ionic form, right?
But according to the examiner, the ionic equation should be CO3+ 2H --->
CO2 + H2O......