(y ml
(4,06 x 10²m2) - (0.0226 X 102 ml calculation round of 3 digits
Answers
Explanation:
In any measurement, the number of significant figures is critical. The number of significant figures is the number of digits believed to be correct by the person doing the measuring. It includes one estimated digit. So, does the concept of significant figures deal with precision or accuracy? I'll answer this question after you peruse the next example.
Let's look at an example where significant figures is important: measuring volume in the laboratory. This can be done in many ways: using
a beaker with volumes marked on the side,
a graduated cylinder, or
a buret.
Which glassware would give you the most precise volume measurement? Let's figure out the volume for each one and its associated error. This will give us the number of figures that are significant. Recall: the number of significant figures includes one estimated digit.
A rule of thumb: read the volume to 1/10 or 0.1 of the smallest division. (This rule applies to any measurement.) This means that the error in reading (called the reading error) is 1/10 or 0.1 of the smallest division on the glassware. If you are less sure of yourself, you can read to 1/5 or 0.2 of the smallest division.
Beaker The smallest division is 10 mL, so we can read the volume to 1/10 of 10 mL or 1 mL. The volume we read from the beaker has a reading error of 1 mL.
The volume in this beaker is 47 1 mL. You might have read 46 mL; your friend might read the volume as 48 mL. All the answers are correct within the reading error of 1 mL.
So, How many significant figures does our volume of 47 1 mL have? Answer - 2! The "4" we know for sure plus the "7" we had to estimate.
Graduated
Cylinder
Look in the textbook for a picture of a graduated cylinder.
First, note that the surface of the liquid is curved. This is called the meniscus. This phenomenon is caused by the fact that water molecules are more attracted to glass than to each other (adhesive forces are stronger than cohesive forces). When we read the volume, we read it at the BOTTOM of the meniscus.
The smallest division of this graduated cylinder is 1 mL. Therefore, our reading error will be 0.1 mL or 1/10 of the smallest division. An appropriate reading of the volume is 36.5 0.1 mL. An equally precise value would be 36.6 mL or 36.4 mL.
How many significant figures does our answer have? 3! The "3" and the "6" we know for sure and the "5" we had to estimate a little.
Buret
Look in the textbook for a picture of a buret. Note that the numbers get bigger as you go down the buret. This is different from the beaker or the graduated cylinder. This is because the liquid leaves the buret at the bottom.
The smallest division in this buret is 0.1 mL. Therefore, our reading error is 0.01 mL. A good volume reading is 20.38 0.01 mL. An equally precise answer would be 20.39 mL or 20.37 mL.
How many significant figures does our answer have? 4! The "2", "0", and "3" we definitely know and the "8" we had to estimate.