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Physics, Chemistry and Biology: Post your doubts here!

ZaqZainab

ZaqZainab

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A plant cell placed in water enlarges but if it is placed in water after boiling its size decreases. WHY???
 
A

Al-Anoud

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i'm sorry ppl...but cud sum1 plz ans. my qs?
Question.1.) Is saying "anti-biotics can cause bacteria to become immune" and saying "anti-biotics cause bacterial ressitance" the same thing?
(IGCSE Biology btw)
 
Iridescent

Iridescent

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Al-Anoud said:
i'm sorry ppl...but cud sum1 plz ans. my qs?
Question.1.) Is saying "anti-biotics can cause bacteria to become immune" and saying "anti-biotics cause bacterial ressitance" the same thing?
(IGCSE Biology btw)
Click to expand...
Yes, it is the same thing. But, we usually use the word 'resistance' for bacteria since 'immunity' is used against diseases.
 
zara.f

zara.f

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does anyone have good revision notes for chemistry paper 3
pleaseeeeeeeeeeeeeeeeeeeeee help!!!!!!!!!!!
 
cookies&cream

cookies&cream

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Nita Mahajan said:
Chemistry DOUBTS - Can anyone solve these for me? plsView attachment 26768View attachment 26769View attachment 26770View attachment 26771 help!!View attachment 26768View attachment 26770View attachment 26771 View attachment 26769
Click to expand...
Q.1. Ans. is C, because when two gases have the same mole ratio, they have the same volume. Further explanation?
no. of moles of NO= vol./24 = 20/24 = 0.8333...
According to equation, ratio NO:NO2 equals 2:2, so both have same no. of moles. Therefore,
no. of moles of NO2= 0.8333... so, vol. of NO2= 20

Q.2. Not really sure, but I'm guessing it's A.. Because for 2 moles of Cu ions, 2 thiosulfate ions were needed for the I2 formed, so 1 mole of Cu needs 1 mole of thiosulfate. Correct me if I'm wrong, please.

Q.7. a) no. of moles of potassium permanganate = vol. x con. = (16.7/1000) x 0.03 = 5.01 x 10^-4
b) mole ratio manganate : iron = 1:5 , so, no. of moles of Fe ions = (5.01 x 10^-4) x 5 = 2.505 x 10^-3
c) no. of moles of anhydrous compound = 2.505 x 10^-3 (Equation above is ionic, so parts of the compound were crossed out, but mole no. is still the same)
So mass of compound = mol. x RMM = (2.505 x 10^-3) x 284 = 0.71142
d) mass of water = hydrated mass - anhydrous mass = 0.98 - 0.71142 = 0.26858 g ----> 0.269 g
no. of moles = mass/RMM = 0.269/18 = 0.0149 <--- divide by no. of moles of anhydrous compound
so, X= 0.0149/(2.505 x 10^-3) = 5.96 = 6 (This is how my teacher taught it)
Q.9 & 10. Never studied concentration of ions in a solution before o.o (teacher wasn't the best)

Hope I helped though :)
Again, please correct me if I'm wrong. Good luck.
 
I

inquisitiveness

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guys im really confused,Minimising air pollution is essential for health and for the environment.
(a) Natural gas is methane.

(ii) Explain why it is dangerous to use a gas fire in a poorly ventilated room.

my answer was incomplete combustion might occur and CO would be formed which is toxic but the answer said "NOT incomplete combustion"
http://papers.xtremepapers.com/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w06_ms_3.pdf
its question 4 btw....and in the examiners report its written All that was required was a realisation that toxic carbon monoxide
would form (as a result of incomplete combustion due to inadequate oxygen supply).
...i dont undrstand why they said NOT incomplete combustion?
 
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