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# Concentration, Moles, and Volume Help watch

1. I am not confused with this question but I am confused with the answer my teacher gave us:

What volume of 0.0400 mol/dm3 calcium hydroxide just neutralises 25.0cm3 of 0.100 mol/dm3 nitric acid? Give your answer to 3sf.

Ca(OH)2 + 2 HNO3 > Ca(NO3)2 + 2H20

My answer was 0.0313 dm3, because after working out the moles for nitric acid, I then worked out the moles for calcium hydroxide by dividing the moles for nitric acid by 2 (due to the 2 in front of the nitric acid). However, my teacher said you have to multiply by 2 rather than divide by 2, which I do not understand because in similar questions, we divided by the number in front of a symbol rather than multiply by it e.g for 3 NaOH + H3AsO4, when working out the moles for arsenic acid I divided by 3 and got the right answer.

Thanks.
2. (Original post by treehome)
I am not confused with this question but I am confused with the answer my teacher gave us:

What volume of 0.0400 mol/dm3 calcium hydroxide just neutralises 25.0cm3 of 0.100 mol/dm3 nitric acid? Give your answer to 3sf.

Ca(OH)2 + 2 HNO3 > Ca(NO3)2 + 2H20

My answer was 0.0313 dm3, because after working out the moles for nitric acid, I then worked out the moles for calcium hydroxide by dividing the moles for nitric acid by 2 (due to the 2 in front of the nitric acid). However, my teacher said you have to multiply by 2 rather than divide by 2, which I do not understand because in similar questions, we divided by the number in front of a symbol rather than multiply by it e.g for 3 NaOH + H3AsO4, when working out the moles for arsenic acid I divided by 3 and got the right answer.

Thanks.
Your process is correct and I got the same volume as you have too. Keep calculating these the way you have done here.
3. (Original post by TutorsChemistry)
You're process is correct and I got the same volume as you have too. Keep calculating these the way you have done here.
Thank you.

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