Neutralization Question

[Temperature101]

---

Members don't see this ad.

How many milliliters of 0.60M HCL are required to neutralize 3.0 grams CaCO3 ?

A. 50 mL
B. 100 mL
C. 200 mL
D. 300 mL

Answer is B.

BR explain it, but I dont get the way they explain it.

 

[chiddler]

How many milliliters of 0.60M HCL are required to neutralize 3.0 grams CaCO3 ?

A. 50 mL
B. 100 mL
C. 200 mL
D. 300 mL

Answer is B.

BR explain it, but I dont get the way they explain it.

3 grams of CaCO3 is 0.03 mol, yes? So that means we need double this amount, 0.03*2 = 0.06 mol of acid to neutralize. The reason it is double is because HCl is monoprotic while each carbonate ion can consume two protons.

0.6 M =0.03*2 / L
L = 0.1

so it's 0.1 liters or 100 mL.

 

[ljc]

Just to help, the balanced equation would be:

2HCl + CaCO3 ----> Ca(2+) + 2Cl(-) + H2CO3

You could also simply realize CO3 has a -2 charge, meaning its oxygens are willing to accept 2 protons.
Once you realize this, it is a simple matter of converting grams -> moles, adjusting based on coefficients, and then finding the volume.

 

[Temperature101]

Just to help, the balanced equation would be:

2HCl + CaCO3 ----> Ca(2+) + 2Cl(-) + H2CO3

You could also simply realize CO3 has a -2 charge, meaning its oxygens are willing to accept 2 protons.
Once you realize this, it is a simple matter of converting grams -> moles, adjusting based on coefficients, and then finding the volume.

It makes sense now... thanks

 

[SaintJude]

It's likely that almost any neutralization reaction that comes up on the MCAT will require you to balance first! I've got to remember that myself.

 

[MedPR]

3 grams of CaCO3 is 0.03 mol, yes? So that means we need double this amount, 0.03*2 = 0.06 mol of acid to neutralize. The reason it is double is because HCl is monoprotic while each carbonate ion can consume two protons.

0.6 M = 0.03 / L
L = 0.1

so it's 0.1 liters or 100 mL.

You lost me there.

 

[chiddler]

You lost me there.

oops. mistake. switch the two numbers! D:

 

[ljc]

oops. mistake. switch the two numbers! D:

Your numbers are still off, I think.

You have 0.03 moles CO3(2-), so you need 0.03*2 moles HCl (per balanced equation) 0.06 moles HCL

Your concentration is 0.6 moles/liter HCl

That means for every liter of solution, you have 0.6 moles HCl
But you don't need 0.6 moles, you need 0.06 moles.
So 0.06/0.6 = 0.1 L, or 100ml

Don't really need to do the math, just think about it:
0.6 moles in 1L, I need one tenth of that, so I need one tenth of a liter.