Decimal Places (2 Viewers)

[someth1ng]

What's the rule for decimal places in Chemistry? I've heard things like, "number of decimal places in the question and in your response are the same", "if the question is in X significant figures, you put your answer in X decimal places" and many others.

What's the actual rule?

I do have a problem when something like a question that has a minimum significant figure of say 2 and your answer is in the hundred...
What would you do then?

 

[golgo13]

Generally follow the decimal places in the question, however if they don't specify most things are 4 sig figs
Hope that helps

 

[jet]

You go by the least accurate value in the question - this is the rule no matter where you are. Your answer is only as accurate as its least accurate value and so it doesn't make sense to report a value to higher accuracy when it isn't that accurate.

So if you have a question with two values - one to one significant figure and one to 5 significant figures, your answer should be to one significant figure.

Or, for example, if you're calculating the molar mass of H₂O, you know H has a molar mass of 1.008 and O has a molar mass of 16.00. So your answer is 18.01 since each value is accurate to only four significant figures even though there are more decimal places in the molar mass of H.

This only applies to experimental measurements. Theoretical values such as mole ratios and things are generally considered to be perfect measurements which are completely accurate.

Usually it refers to significant figures, not decimal places.

 

[iSplicer]

You go by the least accurate value in the question - this is the rule no matter where you are. Your answer is only as accurate as its least accurate value and so it doesn't make sense to report a value to higher accuracy when it isn't that accurate.

So if you have a question with two values - one to one significant figure and one to 5 significant figures, your answer should be to one significant figure.

Or, for example, if you're calculating the molar mass of H₂O, you know H has a molar mass of 1.008 and O has a molar mass of 16.00. So your answer is 18.01 since each value is accurate to only four significant figures even though there are more decimal places in the molar mass of H.

This only applies to experimental measurements. Theoretical values such as mole ratios and things are generally considered to be perfect measurements which are completely accurate.

Usually it refers to significant figures, not decimal places.

Excellent answer.

One more thing: you need to use your common sense in some cases. Let's say you have two quantities: 100,000 and 3.87. How many SF in your answer? =P

 

[someth1ng]

Excellent answer.

One more thing: you need to use your common sense in some cases. Let's say you have two quantities: 100,000 and 3.87. How many SF in your answer? =P

Right, three in your answer?

 

[someth1ng]

Or, for example, if you're calculating the molar mass of H₂O, you know H has a molar mass of 1.008 and O has a molar mass of 16.00. So your answer is 18.01 since each value is accurate to only four significant figures even though there are more decimal places in the molar mass of H.

If the mass was written as 16 instead of 16.00 then you give you answer as 18?

My problem is that, what if the smallest is 3 SF but you have an answer say 1056mL, do you round it to 1060mL?