Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: NewSoul on February 28, 2013, 12:28:56 AM
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Hey guys. For some reason my lab class is ahead of my lecture class, so everyone is always totally lost when it comes to calculations. We are expected to figure these out on our own without any information on how to solve certain equations until after they are due.
Right now I'm stuck on a few problems.
1.) A 0.481g sample of an unknown acid (HX) required 0.02895L of 0.2103M NaOH for neutralization to a phenolphthalein endpoint. What is the molar mass of the acid?
Here is my thought process:
- I first thought about using the formula C1V1=C2V2. However, I quickly realized that I had a unit of g instead of L. This won't work.
- I next noticed that I can find the moles of NaOH. .02895L * .2103M = 0.006088185mol NaOH
- I finally noticed that what I need to somehow calculate the moles of HX. I would be able to do this if I were given a chemical equation and note the ratio between HX and NaOH, but I unfortunately cannot.
I also would like to know if this problem is done the same way as the first one I mentioned. Again, to me it looks like there is missing information because I do not know how to do these types of problems.
2.) What volume of 0.1037M HCl is necessary to neutralize 0.3643g Ca(OH)2?
Thank you very much.
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Show you own attempts.
First 1. Calculate the mole of the NaOH.
2. These has to be equal to the acid because it is HX
3. Calculate the molar mass by using n = m/M in right order.
Second 1. Calculate the mole of Calcium hydroxide
2. Calculate the mole of HCl for that
3. Calculate with the given molarity the volumen