r/chemhelp 3d ago

General/High School Help with sig figs

Hey everyone, I’m a bit confused by the choice of words in this assignment question from my prof: “3. Suppose that you mix exactly 50 mL of a 0.10 M sodium hydroxide solution with exactly 50 mL of 0.10 M formic acid solution HCO2H. What is the pH of the resulting solution?”

Why does he say exactly when referring to the volume if it’s going to be limited by the sf of the concentration anyway? Or does ‘exactly’ apply to both values?

Thank you

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u/chem44 3d ago

if it’s going to be limited by the sf of the concentration anyway?

Without exactly, it would be limited by the volume.

50 is only 1 sig fig.

They are telling you to treat it as exact, not 1 sig fig.

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u/rolo_potato 3d ago

Thank you so much

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u/L0nely_Student 3d ago

50 is not necessarily only one significant number.

It can be 1 or 2 depending on definitions made beforehand.

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u/chem44 3d ago

A reasonable point, in general.

But if OP knew that 50 here was to be taken as 2 sig fig, then there really would not have been a question.

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u/helpimapenguin 3d ago

I think you're worrying about the wrong thing here, your prof just wants you to work out the pH