Determining significant figures? (Chemistry class)?

Question

Can someone explain to me how to determine the significant figures? And how to determine the sig. figs. in addition, subtraction, multiplication, and division. I know that the rule for determining the sig. figs. is different in adding and subtracting than it is for multiplying and dividing, but can someone explain the method please.

Thank You.
=]

Answer 1

The Rock is confused. The zeros in 7.008 are certainly significant. The zeros in 7000 are not because 7000 can also be written as 7 x 10^3.

In multiplying and dividing the number of significant figures in the least significant number are used. So in 1003 x 7 the right answer from a significant figures point of view is 7 x 10^3 (also 7000) because there is only 1 significant figure in the number 7. If the question was 1003 x 7.0 then you would use two significant figures and it would be written as 7.0 x 10^3

Adding and subtracting use the least precise measurement. So for 10 - 0.05 then the answer is 10

For 6 + 6.5 + 6.50 + 6.500 the answer would be 26 because the least accurate number is the 6 which is in the ones place, so the answer is only significant to the ones place.

Hope that helped!!

Good luck!

Answer 2

0's that are just placeholders, like in the number 7.008 are NOT sig digits.

0's in numbers without decimals are NOT sig digits.
Example: The number 90 only has one sig digit.

HOWEVER, if a number ends with 0, that means it is extremely accurate, so the 0 is a sig digit.

Example: 93.80 has 4 sig digits.

If a 0 after the decimal is between two sig digits, it too is significant.

7.707 = 4 sig digits.

For adding and subtracting:

You use the LEAST precise measurement.

For example:

If you multiply 5.7489 x 5.2 your answer will only have ONE decimal place in it, so you have to round.

Same goes for division.

This is all off the top of my head but it's certainly correct.


THAT Guy below me is confused.

7.008 has only two significant digits.