Physics, Chemistry and Biology: Post your doubts here!

[123rods]

Hey for the Bio IGCSE the latest grading threshold (2013) stated that to get an A* you need to get 144 for the paper 12,32,62 option (CY Option). But just above that table they stated the maximum marks possible to be gained is 200 but there are only 160 marks available (40 for paper 12, 80 for paper 32, 40 for paper 62)

 

[omar28744]

Hey for the Bio IGCSE the latest grading threshold (2013) stated that to get an A* you need to get 144 for the paper 12,32,62 option (CY Option). But just above that table they stated the maximum marks possible to be gained is 200 but there are only 160 marks available (40 for paper 12, 80 for paper 32, 40 for paper 62)

they multiply with a scale factor to get it i do not exactly know how it is done

 

[AYK998]

formulas for stoichiometry?????plzzzzz

 

[princess sofia]

how is it A shdnt it be B
plz explain sme1

 

[Gamedos]

how is it A shdnt it be B
plz explain sme1 View attachment 42621

the compass will point to the north as the brass rod is not magnetised

 

[princess sofia]

the compass will point to the north as the brass rod is not magnetised

yeah bt north is upwards , evn thn it shd both point downwards , as feild lines go frm noth to south ,

 

[Gamedos]

yeah bt north is upwards , evn thn it shd both point downwards , as feild lines go frm noth to south ,

compasses always point to the geographical north of the earth ,as thr is no magnet near them,so both will point to the same direction(to the north of the earth)
as they are in the same hemishere

 

[Gamedos]

how is it A shdnt it be B
plz explain sme1 View attachment 42621

which year and seesion is this pp

 

[princess sofia]

compasses always point to the geographical north of the earth ,as thr is no magnet near them,so both will point to the same direction(to the north of the earth)
as they are in the same hemishere

the direction of north is given to us in da question
its from may 2005

 

[princess sofia]

thx one also plz

 

[Gamedos]

thx one also plz

i need to see the whole question

 

[princess sofia]

i need to see the whole question

here u go , Q3

 

[Phoenix Blood]

In electrolysis of CuSo4 using Cu electrodes, Cu2+ ions travel from solution to the cathode and ONLY e- electrons lost by the copper at the anode travels to the cathode. So mass of cathode decreases because of electrons lost, not because of loss of copper?
Awesome12 eureka!

 

[Awesome12]

In electrolysis of CuSo4 using Cu electrodes, Cu2+ ions travel from solution to the cathode and ONLY e- electrons lost by the copper at the anode travels to the cathode. So mass of cathode decreases because of electrons lost, not because of loss of copper?
Awesome12 eureka!

Not i am afraid you are wrong. The copper ions travel to the anode where they are discharged. At the anode, they convert to ions. The reaction is
Cu (s) -------------> Cu+2 + 2e-
So the solid copper is being converted in to copper ions that go in to the solution. So the cathode decreases in mass because copper atoms are being lost

 

[ahmed butt]

guys what to do for physics
i am so stressed
plz help

 

[Phoenix Blood]

Describe the action of heat ( if any) on :

1) Hydroxides of Ca, Cu, Fe, Mg, K, Na, Zn
2) Nitrates of Ca, Cu, Fe, Mg, K, Na, Zn


Awesome12 eureka!

 

[Phoenix Blood]

Why does acidified KMnO4 turn colorless in alkenes?

 

[Akshajistari]

AYK998

formulas for stoichiometry?????plzzzzz

the main ones are:

Number of moles= mass of substance (in grams)/mass of one mole

Number of moles= volume(in dm^3) * concentration of solution.

Number of moles= volume of gas(in dm^3)/ 24

Percentage yield= (actual yield/ theoretical yield) * 100 (all in grams)

Percentage purity = mass of pure substance/ total mass of pure substance ( both in grams)

 

[Zubair Junjunia]

Why does acidified KMnO4 turn colorless in alkenes?

Potassium Manganate is a oxidising agent therefore is reduced itself. As alkenes are unsaturated, they are able to react with the MnO4 ion and that is why it turns colourless

 

[Gamedos]

here u go , Q3

as the water is starting 2 evaporate so energy is used to weaken bonds instead of increasing temp