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# Calculate the number of Aluminium ions present in 0.051g of Aluminium oxide

Asked by Keerthana Vijayan(CHINMAYA VIDYALAYA) , on 28/1/12

BEST ANSWER Certified by MeritNation Expert

1 mole of aluminium oxide (Al2O3) = 2 × 27 + 3 × 16

= 102 g

i.e., 102 g of Al2O3 = 6.022 × 1023 molecules of Al2O3

Then, 0.051 g of Al2O3 contains =

= 3.011 × 1020 molecules of Al2O3

The number of aluminium ions (Al3+) present in one molecule of aluminium oxide is 2.

Therefore, the number of aluminium ions (Al3+) present in 3.011 × 1020 molecules (0.051 g ) of aluminium oxide (Al2O3) = 2 × 3.011 × 1020

= 6.022 × 1020

Posted by Kunal Choudhary(ST CECILIA'S PUBLIC SCHOOL) on 30/1/12

This conversation is already closed by Expert

Given mass = 0.051 g.

Let the given mass be 'm '

Formula of compound 'Aluminium Oxide ' = Al2 O3 .

Formula mass = 102 u (  Al = 27 u and O = 16 u.)

Let the Formula mass be 'M '

Let the number of Aluminium ions present be 'n '.

Let Avagadro no. be 'n0 ' = 6.022 * 1023.

Then n = ( m* n0) / M

= ( 0.051 * 6.022 * 1023 ) / 102

= 0.307122 * 1023 / 102

= 0.003011 * 1023 ions.

= 3.011 * 1021 ions.

Posted by Shobhitanshuon 28/1/12

the above one is wrong because he has found out the no. of ions in Al2O3but didn 't find no. of ions in aliminium

to find that you just multiply the ans by 2

and he has done calculation wrong according to him ans must be

3.011 * 1020

but you multiply it by 2

so ans will be 6.022 * 1020

Posted by Akshay Gahlot(St Pauls Sr Sec SchoolBeawar) on 28/1/12

I am sorry I typed incorrectly as i was typing without seeing the keyboard and by mistake i clicked on Post Answer button after solving only half question. Your answer is right akshaygahlot13...

Posted by Shobhitanshuon 29/1/12

Thanks akshaygahlot and shobhitanshu.

But how did that 2 come from? (u multiplied 3.011 x 1020 by two to get the last answer)

Posted by Keerthana Vijayan(CHINMAYA VIDYALAYA) on 29/1/12