how to answer this question? (1 Viewer)

[RG11]

The ph of a 0.0541 molL^-1 solution of hcl is most correctly expressed as:

A) 1.266803
B) 1.267
C) 1.27
D) 1.3

If the original 0.0541 is 3 sig figs shouldnt the answer be C?

 

[seventhroot]

yes C) for that same reasoning you have

 

[enigma_1]

Noo wait it's not c
I'll explain when I get homep

 

[seventhroot]

Noo wait it's not c
I'll explain when I get homep

...

 

[enigma_1]

...

huh?

Chem is such a corrupted subject.
The rule is that the number of decimal places in pH is the SAME as the number of significant figures in the H+ concentration.

Since in the question, there are 3 sig figs in the H+ concentration given to you, you calculate the pH which is 1.266802735 and then get the SAME NUMBER OF DECIMAL PLACES as the concentration, so to THREE decimal places.

Hence the answer is 1.267 so B.

If you have conquering chemistry the rule is on page 134 hard copy.
It's a useless rule but avoid losing marks on stuff like this.

 

[seventhroot]

is that legit a rule? because you can't get anymore accurate than 3 sig. fig. in this case

 

[enigma_1]

is that legit a rule? because you can't get anymore accurate than 3 sig. fig. in this case

Trust me, it is. Like you can also tell from the question, chem's not that easy. They wouldn't just expect you to find 3 sf answer and move on. There's definitely something else involved. That's where the rule comes in. It's extremely easy to make sillies in chem exams. Made like 6 in my exam ):

proof of the rule

 

[Queenroot]

Dude this thing in Chem fucked me up so bad during HSC. It's so dumb. 3 sig figs is 3 sig figs, HSC chem makes no logical sense equating decimal places to sig figs.

 

[QZP]

Wow never heard of this rule... Can I ask where the question is from OP? I wonder if HSC has had a similar Q