What is the unit for molar mass?and a Q about sigs figs??

[zibb3r]

Hi again ,

1) What is the unit for molar mass? ( g/mol or g/mol^-1)?

2)  When finding the Molar mass of BaSO₄:

137.3+32.1+(4 x 16.0) = 233.4 g/mol^-1

Is this to the right amount of sig figs and decimal places, cuz 16.0 has 1 decimal place???

Thanks

[Andiio]

1) g/mol = gmol^-1 (either one is fine, so for example the Mm of Carbon is 12g/mol or 12gmol^-1)
2) You shouldn't worry too much about sig figs with finding the molar mass (Don't think you'd have many questions asking you to state the molar mass of a certain element/compound - they're used for calculations), rather, you would look at the lowest amount of sig figs the question states and then work from there.

[luken93]

1) g/mol translates to "the amount in grams per mol of a substance"
the g/mol^-1 simply comes from the formula n=m/Mr, where you have m (grams) divided by Mr (mol), hence it is g/mol = g per mol^-1

2) In the exam, the data book only gives the molar mass of elements to 1 decimal place, so you don't really need to worry

[zibb3r]

so does the .0 in 16.0 (oxygen) count a a sig fig??? or do i regard it as 16, which therefore means the answer has no decimal places???

[taiga]

16.0 is three significant figures

233.4 is four significant figures


erase the term "decimal places" from your mind whilst doing chem

[zibb3r]

so..... whats the correct answer then???

[luken93]

so..... whats the correct answer then???

Do you mean in terms of setting out your working on the exam?
If so, then yes you could do this (although don't quote me on it), but to save any dramas just do the Molar Masses on the calculator and write the final value with 1 decimal point, as is shown in the VCAA data book...