Measurement significant figures and

Measurements that are of high precision are usually accurate. It is possible, however, to have a systematic error in a measurement. Suppose that, in calibrating a ruler, the first centimeter is made too small by 0.1 cm.Then, although the measurements of length on this ruler are still precise to 0.01 cm, they are accurate to only 0.1 cm. 

Measurement is the comparison of a physical quantity to be measured with a unit of measurement—that is, with a fixed standard of measurement. On a centimeter scale, the centimeter unit is the standard of comparison. A steel rod that measures 9.12 times the centimeter unit has a length of 9.12 centimeters. To record the measurement, you must be careful to give both the measured number (9.12) and the unit (centimeters). 

To indicate the precision of a measured number (or result of calculations on measured numbers), we often use the concept of significant figures. Significant figures are those digits in a measured number (or result of a calculation with measured numbers) that include all certain digits plus a final one having some uncertainty. When you measured the rod, you obtained the values 9.12 cm, 9.11 cm, and 9.13 cm. You 

All digits are significant except zeros at the beginning of the number and possibly terminal zeros (one or more zeros at the end of a number). Thus, 9.12 cm, 0.912 cm, and 0.00912 cm all contain three significant figures. 

Terminal zeros ending at the right of the decimal point are significant. Each of the following has three significant fignres 9.00 cm, 9.10 cm, 90.0 cm. 

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In discussing measurements and significant figures it is useful to distinguish between accuracy and precision. Accuracy tells us how close a measurement is to the true value of the quantity that was measured. To a scientist there is a distinction between accuracy and precision. Precision refers to how closely two or more measurements of the same quantity agree with one another (Figure 1.12). 

In discussing measurements and significant figures it is useful to distinguish between... 

Both uncertainty in measurement and significant figures are illustrated in Figure 3.7, which has two captions. The first caption focuses on uncertainty, and the second shows how to apply significant figures to the same measurements. Study these captions carefully now, before proceeding to the next paragraph. 

An exact number is a small number that can be reproducibly determined by counting or one that is defined to a particular value. Exact numbers have infinite precision and significant figures. Exact numbers are not obtained using measuring devices. 

Having surveyed some of the units used in chemistry, we now turn to techniques for handling numbers associated with measurements scientific notation and significant figures. 

GPEs contain organic solvents as plasticizers and the reduction of vapor pressure is crucial. The amount of vaporized solvents from our GPE was measured in the experiment described here. Microporous polyethylene separator and the polymer matrix were soaked in the electrolyte solution and heated at various temperatures for 60 min. The vapor amounts from both samples were measured and compared. Figure 2.5 clearly shows that the vapor pressure of solvents in our GPE was significantly low even at the temperature of TOO °C, while microporous separator could hold the solution at low temperature probably due to large surface tension in the micropores, but vaporization of solvents increased steeply as the temperature rose. 

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