Chem (2 Viewers)

[Luukas.2]

View attachment 39872
shouldnt it be 2.40 x 10^-5
bc u get 2.3979... x 10^-5

Short answer... yes.

Long answer... calculation is flawed, boric acid does not ionise to produce H₂BO₃^-, thought I am sure this is what you are intended to do.

 

[Luukas.2]

View attachment 39873
shouldnt it be both 1 sf bc the ph is to 1dp @carrotsss
no trial paper follows these rules and each trial paper makes up their own mf rules when it comes to ph i wanna die

Technically, yes. Exams are often written sloppily.

In the "official" answer that you posted, for example, I have no idea:

• what log^-5.1 means
• how whatever it is equals pH
• why, since they are finding a concentration, the answer has no units.

Further, (b) should be (taking the weak acid as HA and assuming it is monoprotic):

​

and, given the precision we have, a better answer would be pK_a is 9.2 or K_a = 10^-9.2

 

[Luukas.2]

View attachment 39878
when we draw structural formula tho we put a negative on top of O and positive on top of Na but here we dont need to?

I wouldn't include charges in writing a formula, just like I wouldn't write sodium hydroxide as Na⁺OH^- rather than NaOH.

I would give charges if I was howing a structure where I was noting the ionic rather than covalent bonding... and I would never put something like

CH₃(CH₂)₁₂-C(=O)-O-Na​

as it implies the existence of covalent bonding between the O and the Na, and this is untrue.

I would say that any of

• CH₃(CH₂)₁₂COONa
• CH₃(CH₂)₁₂CO₂Na
• CH₃(CH₂)₁₂COO^- Na⁺
• CH₃(CH₂)₁₂CO₂^- Na⁺

and any similar answers should be accepted for a question like this.

 

[synthesisFR]

I wouldn't include charges in writing a formula, just like I wouldn't write sodium hydroxide as Na⁺OH^- rather than NaOH.

I would give charges if I was howing a structure where I was noting the ionic rather than covalent bonding... and I would never put something like

CH₃(CH₂)₁₂-C(=O)-O-Na​

as it implies the existence of covalent bonding between the O and the Na, and this is untrue.

I would say that any of

• CH₃(CH₂)₁₂COONa
• CH₃(CH₂)₁₂CO₂Na
• CH₃(CH₂)₁₂COO^- Na⁺
• CH₃(CH₂)₁₂CO₂^- Na⁺

and any similar answers should be accepted for a question like this.

Yeah bc when u write in condensed structural formula u put the charges in to indicate those specific bonds r ionic withing the compound so just needed to know whether that extends to condensed formula.

Btw thank u for all ur responses, r u in y12?