calculate the number of moles of HCl originally present.

sarah1004 · #1 Oct 21, 2009, 04:00 PM

A 38.0mL solution 0.026M solution of HCl reacts with a 0.032M NaOH.
a)calculate the number of moles of HCl originally present.
b)how many moles of NaOH are needed to neutralize the acid?
c)calculate the volume of the NaOH required to react completely with the acid

Please help me!

Perito · Oct 21, 2009, 05:10 PM

Quote:

A 38.0mL solution 0.026M solution of HCl reacts with a 0.032M NaOH.
a)calculate the number of moles of HCl originally present.
b)how many moles of NaOH are needed to neutralize the acid?
c)calculate the volume of the NaOH required to react completely with the acid

a) You have 38 mL of 0.26 Molar solution. 0.26 Molar means 0.26 Moles per liter.

$\frac {moles}{liter} \, \times \, \frac {liters}{1} = moles$

So, all you have to do is this:

$\frac {0.026\,moles}{Liter} \,\times\, \frac {38\,mL}{1} \,\times\, \frac {1\,Liter}{1000\,mL} = 0.000988 \, moles$

b) Write the complete reaction and balance the equation.

$HCl + NaOH \rightarrow H_2O + NaCl$

Now you can see how many moles of NaOH react with 1 mole of HCl. Can you see what it is? Then all you do is multiply that number by the number of moles of HCl you calculated in part a). Then you have the answer.

3) You know the concentration of NaOH (0.032 moles/Liter). Use logic similar to what I used in a) to figure out the volume of NaOH you'll need.

sarah1004 · Oct 21, 2009, 05:30 PM

Quote:

Originally Posted by Perito

a) You have 38 mL of 0.26 Molar solution. 0.26 Molar means 0.26 Moles per liter.

$\frac {moles}{liter} \, \times \, \frac {liters}{1} = moles$

So, all you have to do is this:

$\frac {0.26\,moles}{Liter} \,\times\, \frac {38\,mL}{1} \,\times\, \frac {1\,Liter}{1000\,mL} = 0.00988 \, moles$

b) Write the complete reaction and balance the equation.

$HCl + NaOH \rightarrow H_2O + NaCl$

Now you can see how many moles of NaOH react with 1 mole of HCl. Can you see what it is? Then all you do is multiply that number by the number of moles of HCl you calculated in part a). Then you have the answer.

3) You know the concentration of NaOH (0.032 moles/Liter). Use logic similar to what I used in a) to figure out the volume of NaOH you'll need.

i dont understand it

sarah1004 · Oct 21, 2009, 05:31 PM

I mean why you using 0.26 moles? how did you get that number?

Unknown008 · Oct 22, 2009, 12:09 AM

Actually, Perito misread the question, where the molar concentration is 0.026 M and not 0.26 M