[princemac]

Hi everyone,

Can anyone help me with these two questions:

1. the net ionic equation for

KOH + NaHSO₄

I think it might be  K⁺ + HSO4^- ->  KHSO₄
Am I correct?


Also this question

If one mixes 50mL of NaOH solution at 25.15 C  with a 25mL solution of HCL at 26.34 C what would be the final temperature of the solution before any reaction occurs between HCL and NaOH?

What I did was

using m₁C(delta T) = m₂c(delta T)

with c = that of water and m₁=50g and m₂=25g since it is mostly water

delta T = T_final - T_initial for the two solutions and then find T final to be 23.96 C

Am I on the right track here??

Thanks a lot for any help.

[Borek]

I think it might be  K⁺ + HSO4^- ->  KHSO₄

This is an acid base reaction.

Am I on the right track here??

I have not checked the numbers, but at first sight what you did looks OK.

[DrCMS]

Hi everyone,

Can anyone help me with these two questions:

1. the net ionic equation for

KOH + NaHSO₄

I think it might be  K⁺ + HSO4^- ->  KHSO₄
Am I correct?

No, write out the full reaction with reactants on one side and products on the other.  Now cancel all the ions that are common to both sides.  What you have is the net ionic reaction for and acid base neutralisation.

If one mixes 50mL of NaOH solution at 25.15 C  with a 25mL solution of HCL at 26.34 C what would be the final temperature of the solution before any reaction occurs between HCL and NaOH?

What I did was

using m₁C(delta T) = m₂c(delta T)

with c = that of water and m₁=50g and m₂=25g since it is mostly water

delta T = T_final - T_initial for the two solutions and then find T final to be 23.96 C

Am I on the right track here??

No think about it again to you have two solutions at 25+^oC that you mix together will they be more or less than 25^oC afterwards.

[Borek]

Sorry, I must have switched the numbers. I was sure final result was between temperatures given. DrCMS is obviously right.

Still, approach is correct, my bet is that you have changed the sign somewhere.

[princemac]

Oh! stupid me, I didn't realize it is an acid base reaction, so the net ionic would be
H⁺ + OH^- H₂O_(l)

I was confused at the thought of KNaSO₄


As for the second problem, I'm still not getting the answer, I double checked the calculations and they seem to be correct.

M_NaOH C_H2O :delta: T = M_HCL C_H2O :delta: T


(50grams) (C) (T_final - 25.15)  =  (25grams) (C) (T_final - 26.34)


(50grams) (T_final - 25.15)  =  (25grams) (T_final - 26.34)


[ (50) (T_final) ] - (1257.5)  =   [ (25) (T_final) ] - (658.5)


[ (50) (T_final) ] - [ (25) (T_final) ]  =   (1257.5)  - (658.5)


[ (25) (T_final) ]  =   (1257.5)  - (658.5)


[ (25) (T_final) ]  =   599


[ (25) (T_final) ]  =   23.96



I agree with DrCMS but according to Borek the method is right and the calculations are right. Unless the method is wrong. I don't know of any other method to solve this...does the problem occur because it says "before any reaction occurs?"

If the method is wrong, what method to use to solve it?
Thanks for any help.

[sjb]

Oh! stupid me, I didn't realize it is an acid base reaction, so the net ionic would be
H⁺ + OH^- H₂O_(l)

I was confused at the thought of KNaSO₄


As for the second problem, I'm still not getting the answer, I double checked the calculations and they seem to be correct.

M_NaOH C_H2O :delta: T = M_HCL C_H2O :delta: T


(50grams) (C) (T_final - 25.15)  =  (25grams) (C) (T_final - 26.34)
...

Shouldn't this perhaps be

(50grams) (C) (T_final - 25.15)  =  (25grams) (C) (26.34 - T_final)

[Borek]

Yep, that's this "sign" thing I referred to in my previous post. In general for closed system

heat gained + heat lost = 0

so we often write it as

heat gained = -heat lost

but it is also quite often written as

heat gained = heat lost

which is correct if the sign change is moved to delta T. This is often confusing.

[princemac]

Ahhh!!!!!

I've gone from confused to upset to depressed. I had an exam the other day and this second problem was there for 10 extra marks (no partial marks was given) I was the only one using this method, that is why i was confused at first why I got it wrong because I was sure this was the right way.

Thanks for clearing up my confusion. The answer is 25.5 C