Assignment Question... (1 Viewer)

[Althea]

Hey there,

Could anyone please help me with this assignment question?

Sodium carbonate is mixed with an excess of hydrochloric acid. The reaction mixture lost mass, due to 700 mL of carbon dioxide gas escaping.

If the mixture was evaporated to obtain sodium chloride crystals, what mass of NaCl (s) whould be obtained? The molar volumes of gases at 100.0kPa and 25*C is 24.784 L.

Ahh - just can't get it! Too much of this for one day... thanks in advance for any help.


Blanker - Althea.

 

[Xayma]

Ok work out how many moles of CO₂ gas escaped (by comparing the volumes) then use stoich to figure out how many moles then work out the mass from that.

 

[Althea]

....thanks Xayma.

 

[scotty schaefer]

What answer did you get Xayma? So I can check it with mine, I think I'm wrong.

 

[Xayma]

I dont know I never did it.

But I will do it know.

Na₂CO_{3 (s)}+2HCl_(aq)---> 2NaCl_(aq)+CO_{2 (g)}+H₂O_(l)

Now 700ml=0.7L
n_CO₂=.7/24.47
=0.0286mol

By Stoich n_NaCl=2n_CO₂
.: n_NaCl=0.0572mol

m=nM
(From memory Sodium is 22.99 and Chlorine is 35.45 but dont hold me to that)

m=0.0572*(22.99+35.45)
m=3.343g

And why was the NaCl formed as a solid? Shouldnt it go into solution?

 

[CM_Tutor]

Just one small correction. The question says at 100.0 kPa, so you need to use V_1mol = 24.784 Lmol^-1, rather than the 101.3 kPa value of V_1mol = 24.47 Lmol^-1 that Xayma has used.

So, n(CO₂) = 0.700 / 24.784 = 0.02824 ... mol, and the final answer becomes 3.30 g (3 sig. fig.)

 

[scotty schaefer]

Cool, I did get it right. Thanks guys!!

 

[Althea]

Yay - I got mine right too!

Thanks for everyones help!

 

[Xayma]

Hmm I suprised I actually remembered the volume for 101.3KPa *opps