AChapel Posted September 16, 2008 Report Share Posted September 16, 2008 How do you know how many significant figures to use in an example like this:12.3gO x 1 mol/16.00gO = XThere is only one significant figure in the moles (one) so do I use that or do I go by the actual numbers?Thanks! Reply Link to post Share on other sites More sharing options...
Solaris Posted September 23, 2008 Report Share Posted September 23, 2008 (edited) How do you know how many significant figures to use in an example like this:12.3gO x 1 mol/16.00gO = XThere is only one significant figure in the moles (one) so do I use that or do I go by the actual numbers?Thanks!You have to consider the decimal points. The maximum number decimal place, is 1 as in 12.3. So change everything to 1 decimal digit. so you get 12.3g x 1.0 mol/16.0g = 0.8 mol Edited September 23, 2008 by Solaris Reply Link to post Share on other sites More sharing options...
IBdoc Posted September 23, 2008 Report Share Posted September 23, 2008 You have to consider the decimal points. The maximum number decimal place, is 1 as in 12.3. So change everything to 1 decimal digit. so you get 12.3g x 1.0 mol/16.0g = 0.8 molAre you sure? I thought that you only consider decimal places when it comes to addition or substraction but for multiplication and division you consider the least number of significant figures. Can anyone confirm this? Reply Link to post Share on other sites More sharing options...
Solaris Posted September 23, 2008 Report Share Posted September 23, 2008 (edited) Oh, sorry. Just Confirmed it. It only applies to addition and subtraction. Multiplication and DivisionWhen experimental quantities are multiplied or divided, the number of significant figures in the result is the same as that in the quantity with the smallest number of significant figures. If, for example, a density calculation is made in which 25.624 grams is divided by 25 mL, the density should be reported as 1.0 g/mL, not as 1.0000 g/mL or 1.000 g/mL. Edited September 23, 2008 by Solaris Reply Link to post Share on other sites More sharing options...
moneyfaery Posted September 23, 2008 Report Share Posted September 23, 2008 How do you know how many significant figures to use in an example like this:12.3gO x 1 mol/16.00gO = XThere is only one significant figure in the moles (one) so do I use that or do I go by the actual numbers?Thanks!The units are g and g/mol, where mol is exactly 1 mol (so 1.00000000 mol etc). Therefore, there are 3 sig digs.12.3g / 16.00g/mol = 0.769mol Reply Link to post Share on other sites More sharing options...
Solaris Posted September 24, 2008 Report Share Posted September 24, 2008 (edited) The units are g and g/mol, where mol is exactly 1 mol (so 1.00000000 mol etc). Therefore, there are 3 sig digs.12.3g / 16.00g/mol = 0.769molI think it should be the lowest number of significant digits in the calculations, which makes it:12.3g / 16 g/mol = 0.77 molThe maximum number of significant figures is 2 (as in 16). Edited September 24, 2008 by Solaris Reply Link to post Share on other sites More sharing options...
IBdoc Posted September 24, 2008 Report Share Posted September 24, 2008 I think it should be the lowest number of significant digits in the calculations, which makes it:12.3g / 16 g/mol = 0.77 molThe maximum number of significant figures is 2 (as in 16).No, the trailing zeros in the 16.00 are there for a reason. You can't just take them off! So the person above you is right the least number of significant figures is 3. Reply Link to post Share on other sites More sharing options...
Solaris Posted September 25, 2008 Report Share Posted September 25, 2008 No, the trailing zeros in the 16.00 are there for a reason. You can't just take them off! So the person above you is right the least number of significant figures is 3.Uh, ok. But if you are right than we also need to change 12.3 to 12.30 Reply Link to post Share on other sites More sharing options...
IBdoc Posted September 25, 2008 Report Share Posted September 25, 2008 Uh, ok. But if you are right than we also need to change 12.3 to 12.30No, that's the way they gave it to you 12.3 and 16.00 so you can't add or take off digits. It's a given that 12.3 has 3 sig. fig. and 16.00 has 4. Reply Link to post Share on other sites More sharing options...
xsandralee Posted October 1, 2008 Report Share Posted October 1, 2008 sig fig rules for addition and subtraction: smallest sig fig. ex) 24 + 20 = 26 = 30sig fig rule for multiplication and division: smallest decimal pointex) 2.5 x 3 = 7.5 = 8 Reply Link to post Share on other sites More sharing options...
moneyfaery Posted October 1, 2008 Report Share Posted October 1, 2008 sig fig rules for addition and subtraction: smallest sig fig. ex) 24 + 20 = 26 = 30sig fig rule for multiplication and division: smallest decimal pointex) 2.5 x 3 = 7.5 = 8Incorrect, actually. Addition and subtraction: keep the least number of decimal placesex) 1.38 + 3.93 + 2.2 = 7.5Multiplication and division: keep the least number of significant digitsex) 2.593 * 94.2 / 3.1930 = 74.5Counting the number of sig digsTrailing zeroes AFTER the decimal place countex) 3.00 has 3 sig digsTrailing zeroes before the decimal place do NOT count UNLESS there is a decimal place 3200 has 2 sig digs 320. has 3 sig digs 320.0 has 4 sig digsLeading zeroes do not countex) 0.0000291 has 3 sig digs 0.003200 has 4 sig digs 004 has 1 sig digZeroes between numbers DO countex) 605 has 3 sig digsAll non-zero numbers countex) 483 has 3 sig digsSCIENTIFIC NOTATION is often useful when calculating with sig digsex) 0.0003200 has 4 sig digsconverted to 3 sig digs = 3.20 x 10-4converted to 2 sig digs = 3.2 x 10-4ex) 30000 has 1 sig digconverted to 2 sig digs = 3.0 x 104converted to 3 sig digs = 3.00 x 104 1 Reply Link to post Share on other sites More sharing options...
IBdoc Posted October 3, 2008 Report Share Posted October 3, 2008 Ok the guy above me got it all right! Thanks. Reply Link to post Share on other sites More sharing options...
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