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# Pastpaper question. Help needed plz! watch

1. How many moles of ions are present in 30 cm3 of 0.025 mol dm-3 barium hydroxide solution, Ba(OH)2(aq)?

A) 0.00075

B) 0.00150

C) 0.00225

D) 0.00450

What i did is that i found out moles first then multiplied by Avagadro Constant which gives answer A. But its wrong. The answer is C.

Can anyone explain me in a detailed manner please? Thank you for your time
2. So you have calculated the moles first which is correct. How many ions are formed in a solution of barium hydroxide?
3. You don't need to multiply by Avagadro's constant as the question is asking about moles not molecules.

The number of moles of Ba(OH)2 is the same as A, but you're looking for the number of ions. How many ions are there in Ba(OH)2?
4. (Original post by JAR123)
So you have calculated the moles first which is correct. How many ions are formed in a solution of barium hydroxide?
3? 2 of OH and 1 of Ba
5. (Original post by EierVonSatan)
You don't need to multiply by Avagadro's constant as the question is asking about moles not molecules.

The number of moles of Ba(OH)2 is the same as A, but you're looking for the number of ions. How many ions are there in Ba(OH)2?
3? 2 of OH and 1 of Ba
6. What year are you in?
7. (Original post by dajjal619)
3? 2 of OH and 1 of Ba
Exactly so multiply your mol value by 3
8. (Original post by dajjal619)
How many moles of ions are present in 30 cm3 of 0.025 mol dm-3 barium hydroxide solution, Ba(OH)2(aq)?

A) 0.00075

B) 0.00150

C) 0.00225

D) 0.00450

What i did is that i found out moles first then multiplied by Avagadro Constant which gives answer A. But its wrong. The answer is C.

Can anyone explain me in a detailed manner please? Thank you for your time
Moles = Concentration x Volume
Moles = 0.03 x 0.025 = 0.00075
Moles Ba ions = 0.00075
Moles OH ions = 0.00075 x 2= 0.0015
Total moles of ions = 0.00225
9. (Original post by EierVonSatan)
Exactly so multiply your mol value by 3
Thanks Sir! got it
10. (Original post by Agrey)
Moles = Concentration x Volume
Moles = 0.03 x 0.025 = 0.00075
Moles Ba ions = 0.00075
Moles OH ions = 0.00075 x 2= 0.0015
Total moles of ions = 0.00225

Yes Got It. Thanks

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Updated: February 25, 2018
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