![]() ![]() Is used to express a measurement greater than 1, the original number is expressedĪs a number between 1 and 10 multiplied by 10 n, where n ![]() Shows the decimal equivalent of some powers of 10. WhenĮxponential notation is used, the measurement is expressed as a number betweenġ and 10 multiplied by a power of 10. Numbers, we use exponential notation (also called scientific notation). To simplify the writing and tabulating of such Such numbers are hard to deal with, difficult to copy without making mistakes,Īnd almost impossible to name. Mass of a hydrogen atom = 0.000 000 000 000 000 000 000 001 67 gĪt the opposite extreme is the mass of the Earth: Measurements in chemistry often involve very large or very small numbers.Īn example of a very small number is the mass of a hydrogen atom, given by: Precision is not enough the determinations must also be accurate. The results obtained on these samples must be accurate within the range allowed. Periodically, accrediting agencies send the laboratories samples to analyze. For this reason, instruments used in medical laboratories are calibrated each day (and often at the beginning of each shift) against samples of known concentrations. Patients and doctors alike want to be certain that instruments give readings that are both precise and accurate. The importance of obtaining measurements that are both accurate and precise is rarely greater than in a medical laboratory. Note that accuracy requires precision, but precision does not guarantee accuracy. However, it is not accurate because the odometer itself is not properly calibrated. The odometer reading is precise because it can be reproduced time after time. Each time it is used on the trip, the inaccurate odometer records the same value of 519 km. However, an odometer that reads 1.00 km for every 0.05 km traveled will measure the Detroit-Chicago distance as 519 km. ![]() An accurate odometer - one that reads 1.00 km for every kilometer traveled - measures the distance between these two cities as 493 km. For example, the driving distance between Detroit and Chicago is 493 km. If it reads only 0.95 km for each kilometer driven, the accuracy of your measurement will be reduced.Ī precise measurement is one that can be reproduced. For example, if you are measuring the distance between two cities by driving between them, an accurate measurement requires that the odometer in your car read 1.00 km for each kilometer driven. The accuracy of a measurement depends on the calibration of the tool used to make the measurement. Measurements in chemistry must be both accurate and precise (Figure 2.4).įIGURE 2.4 Accuracy and precision: Accurate measurements are close to the true value precise measurements are close to one another.Īn accurate measurement is one that is close to the actual value of the property being measured. Chemistry is an exact science its development has been based on careful measurements of properties of matter and careful observations of changes in these properties. ![]()
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