Significant Figures (Sig Figs)?

Question

Can anyone inform me of the rules regarding significant figures in chemistry? Specifically, if you add/subtract/multiply/divide 2 or more numbers together and all have different amounts of sig figs, how many sig figs should be in the answer?

Thank you!

Answer 1

Next time try to get a workshee from the teacher on this stuff ....trust me thats how I got it. Anyway here goes....

whole number such as : 123, 14,103, 155...etc - without end zeroes are counted just the way they are presented

However, numbers such as : 120, 200, 50....etc have zeroes at the end are usually fought over. for scientists believe that zereos at the end of numbers without the additon of a decimal point are not considered to be signifcant digits. thus the # of sig.figs for 120 is 2 ; for 200 is 1 ; for 50 is 1. Be care ful if it is written as : 120. or 200.0 or 50. because then all the digits are considered to be countable and so it would be considered as a whole number.

Now for zeroes before a decimal point and even after a decimal point such as : 0.0008 or 0.5 or 0.0000009 are not counted. thus the # of sig.figs are : 0.0008 has 1; 0.5 has 1; and 0.0000009 has 1.

However if there are zeroes sqashed between non - zero digits [ doesnt' matter if there is decimal or not] they are counted.Such as 105; 200000009; 23.000500; Now the # of sig.figs are 105 has 3; 200000009 has 9; 23.000500 has 6 [ the zeroes at end do not count because there is no nonzeroe digit to ensure their safety]. Only exception that doesn't consider all these rules are the scientific numbers. such as 4.0x10^3 or 5.64x10^5 or 1.0000x10^-9.....etc. In order [ in counting the # of sig.figs: 2 ; 3; and 5.

Now in multiplication and division the number that has the least amount of sig.figs will affect the amont of sig.figs the answer will have - and this includes scientific numbers as well. For example : 506/20.0 = 25.3. Now the # with the least amount of sig.figs is 20.0 because it has 2 sig.figs while 506 has 3 sig.figs. thus 25.3 will be rounded to 25.0 .

Now for addtion and subtraction the factor or added that has the least amount of digits after the decimal point will acount for how much the answer should have after its decimal point. For ex: 20.785- 12.4 = 8.385 As we can see here 12.4 only has one digit after the decimal point while 20.785 has 3 digits after the decimal point. Therefore, 8.385 will round to 8.4 and the answer has 2 sig.figs.

i hope this helped. and if it still doesn't then i suggest to go to a city library and check out books labeled as
Chemistry for dummies - no offense i use it too
the Complete Idiot's guide to Chemistry
Chemistry the Easy Way.
Good Luck!!!!

Answer 2

In addition and subtraction, your answer cannot have more significant figures than the smallest number in those you add. So, for example, 1.1 + 4.307 = 5.4.

In multiplication and division, your answer cannot have any more significant digits than the fewest in the numbers you're crunching. So, 4.3 (2 sig fig) X 7.98432 (6 sig fig) = 34 (2 sig fig)

Hope this helps...

Answer 3

I like the first answer, except:

Adding/subtracting sig figs, you need to go with the answer that has its last sigfig the furthest to the left.

IE,
.000006 has one sig fig

29.36 has four sig figs

But you can't add them to get 29.360006.