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Edexcel CHEMISTRY DOUBTS!!!!

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Alaa Mounier:
can anyone solve this question?
A- Aluminum is extracted by electrolysis of Al2O3. What is the maximum mass of the metal that could be obtained from 1 tonne of the oxide?
B- If the yield of the electrolysis plant is 90%. What mass of the oxide must be used to produce 1 tonne of aluminum?  >:(

conquerpro:
can anyone please solve this question?i need it ASAP.when excess calcium is added to water what is observed?

Candiah:
When Calcium is added to water it fizzes (efferevescence); water turns milky or cloudy. Calcium hydroxide is not very soluble in water.
Ca + 2H20 -----> ca(OH)2  + H2

conquerpro:
what is the oxidation state of ozone O3?

Candiah:
Io3-  + 5 I-  + 6H+      -----> 3I2  + 6H2O

s2O3--  + I2 ------> S4O6-- + 2 I-

so IO3-   ie equivalent to 3 I2 equivalent to 3 S2O3--

moles of thiosulphate = 30 x 0.5/1000  = 15 x 10-3
moles of iodate = 15 x 10-3 /3  = 5 x 10-3

25 cm3  =====  5 x 10 -3
1000  ======= 5 x 10-3   x  1000/25

0.2 mol dm-3

sorry about the upper and lower case I can't do them

sorry i don't know how to do upper and lower cases

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