Please help!! chem exam tommorow =[ (1 Viewer)

[envyaya]

Hey,

I have an end of year chemistry exam (Year 11) tommorow and need help with 2 questions:

Which one of the following compounds, if dissolved in water, would produced a solution with a pH greater than 7

a) KCL
b) KCH3COO
c) KNO3
d) CH3COOH

Well I'm thinking it can't be a or c because they would completely dissociate into ions meaning they would be acidic?

But im not sure between b or d.


and also:

Which of the following species is likely to be most abundant in 1mol L-1 solution of NH4Cl:

a) NH4+
b) Cl-
c) H30+
d) OH-

So NH4CL dissociates into NH4+ + CL-

and successful ionizations

NH4+ + H20 --> NH3(g) + H30+

CL- + H2O --> HCL + OH-

since H30+ and OH- are gained from the successful ionizations I figure they will be less abundant than NH4+ and CL-?

But which of NH4+ and Cl- will be more abundant and why?

 

[brenton1987]

Which one of the following compounds, if dissolved in water, would produced a solution with a pH greater than 7
a) KCL
b) KCH3COO
c) KNO3
d) CH3COOH

Option B.
The salts in A and C are made from the reactions of strong acids with strong bases. They will neutralise at pH7. Option D is a weak acid so it will be < 7. The salt in B is made from a weak conjugate acid and strong conjugate base so in solution it is basic.

Which of the following species is likely to be most abundant in 1mol L-1 solution of NH4Cl:
a) NH4+
b) Cl-
c) H30+
d) OH-

Option C.
The ammonium ion will dissociate into ammonia and protons but the reaction of chloride to form HCl wont happen because it completely dissociates. The ions in solution will be NH₄⁺, NH₃, H₃O⁺ and Cl^-.

 

[xiao1985]

agreed on first q

for q2, you mean B right, bre?

 

[morganforrest]

agreed for Q1

Q2, B yeah?

 

[brenton1987]

for q2, you mean B right, bre?

Yeah I meant B.