Significant Figs or Consistent Decimals?

[master135]

Does IB require consistency in the significant figures for DCP or do they want consistency in the decimal place?

For example: 12 and 0.75 both have 2 significant figs

whereas 12.00 and 0.75 have a consistent 2 decimal place values

[Hyperbole]

I'm no expert, but I'd say that sig figs > consistency of decimal place. Definitely. You should never give data to a higher degree of accuracy than you have been able to measure it, independently of how many decimal places you have for other measurements.

[Abu]

It's nearly always 3 SF.

[SharkSpider]

Any given measuring implement can measure to a certain degree of accuracy, and it is apparent that the higher the measurments, the more relative accuracy you will have. Use consistent decimals, because no instrument exists that gives a sig-fig dependant answer.

[Hedron123]

In the case of exams, you should express your answers with the least number of significant figures, considering the data you receive.

For instance:

33.7 cm3 of HCl neutralises 20cm3 of aqueous Na2CO3 with a concentration of 1.37 mol dm-3. Determine the concentration of the acid.

2 HCl + Na2CO3 ----------> 2NaCl + CO2 + H2O

33.7cm3 HCl _______ 20cm3 Na2CO3 1.37 mol dm-3

1000 cm3 of Na2CO3 _____ 1.37 mol dm-3

20 cm3 ____ 0.0274 mol dm-3

1 mol Na2CO3 _____ 2 mol HCl

0.0274 mol ____ 0.0548 mol of HCl

0.0548 mol ___ 33.7 cm3

1.6 mol ____ 1000cm3

Notice that as we received a value with 2 significant figures (20 cm3) your final answer should be given correct to two significant figures (1.6). Anyway, in the exam they can only deduct 1 point in the overall count for these kind of mistakes.

[__inthemaking]

Sig figs, definitely.

[moneyfaery]

Any given measuring implement can measure to a certain degree of accuracy, and it is apparent that the higher the measurments, the more relative accuracy you will have. Use consistent decimals, because no instrument exists that gives a sig-fig dependant answer.

This, really. If you want to be consistent, use decimal places when recording data. Sig figs should be reserved for calculations.

[master135]

A few of you are saying to use decimals while the rest say sig figs

Is there no way to find out for sure what IB wants?

Edited March 13, 2009 by master135

[Sandwich]

Basically the rule is to use three significant figures UNLESS you are taking a reading from something with a particular level of accuracy. For instance if I were measuring something in a burette which was accurate to the nearest 0.1ml, I would give my reading as 15.0 to show it up to the last decimal point of accuracy.

In the sciences you should definitely go by accuracy of instrument (and therefore decimal places). The only exceptions are in calculations where you're not showing any accuracies and therefore should go to 3 sf (or whatever seems most sensible to reflect your results).

[Vvi]

In exams, it almost always says on the cover sheet. On the Maths exams, it says "Unless otherwise stated in the question, all numerical answers must be given exactly or correct to three significant figures".

People lose a ton of marks over this because they either round to the nearest whole number or not at all. All the little "1 mark"s add up in the end and can bring your grade down by one number.

[moneyfaery]

In exams, it almost always says on the cover sheet. On the Maths exams, it says "Unless otherwise stated in the question, all numerical answers must be given exactly or correct to three significant figures".

Vvi, OP is talking about IAs as he said 'DCP' i.e. Data Collecting and Processing. I still stick to what I said: decimals if recording data, sig figs if making calculations.

For the exam though, it's obviously sig digs - the exams are written in a way so that sig digs are consistent and you don't have a tough time figuring it out.

[deissi]

Viivi: this doesn't really apply for Group 4 calculations, where you don't really go by 3 significant digits, at least not as a rule.

sandwich outlined the way of processing data correctly:

1) When measuring for raw data, use the amount of decimal places that your measuring device is accurate in: if it is a standard ruler, you'll quote your answer with 1 decimal point when using centimeters: 5.1 cm. If it is a scale accurate to 1 gram, you'll quote your answer to the nearest gram: 52 grams. If it is a syringe accurate to 1 ml, you quote it to the nearest milliliter: 13 ml.

2) When calculating, the answer will be displayed using significant figures. The amount of significant figures is the number of significant figures in the raw data with the least significant figures. For example, we can consider the following data:

12 ml of water (2 sf)

123 mm long wire (3 sf)

1251 g mass of water (4 sf)

The processed data would then be shown to 2 significant figures.

[IB_sucks]

In physics, we are told to use the sig figs. When multiplying or dividing values, the answer is supposed to have as many sig figs as the the value with the least amount of sig figs. When adding or subtracting, the answer should have as much sig figs as the number with the least amount of decimal places. Hope this helps