Scientific Measurement Chapter 3 Scientific Measurement

Scientific Measurement Measurement-is a quantity that has both a number and a unit Ex. 12 inches, 5 cm   Measurements are fundamental to the experimental sciences. For that reason it is important to be able to make measurements and decide whether those measurements are correct. Scientific notation- a given number is written as the product of two numbers: a coefficient and 10 raised to a power. Ex. 6.9 x 105

Accuracy and Precision Accuracy-is a measure of how close a measurement comes to the actual true value.   Precision- is a measure of how close a series of measurements are to one another. To evaluate the accuracy of a measurement, the measured value must be compared to the correct value. To evaluate precision of a measurement you must compare the values of two or more repeated measurements.

Scientific Measurement Accepted value-correct value based on reliable reference   Experimental value-value actually measured in the lab. Error- is the difference between experimental value and accepted value Error = experimental value – accepted value

Percent Error Percent error- is the absolute value of the error divided by the accepted value, multiplied by 100% Percent error= error X 100% accepted value

International System of Units (SI) The five SI base units used by chemists are the meter, the kilogram, the Kelvin, the second, and the mole. Table 3.1 in the book. Common metric units of mass are the kilogram, gram, milligram, and microgram.

Scientific Measurements Weight - is a force that measures the pull on a given mass by gravity.   Mass-measure of the amount of matter an object contains Temperature is a measure of how hot or cold an object is.

Scientific Measurements Scientist commonly use two equivalent units of temperature the degrees Celsius, or the degrees Kelvin Celsius water freezes at 0 degrees and boils at 100 degrees Kelvin- water freezes 273.15 and boils 373.15 Conversions  K=C + 273 C= K – 273  Absolute zero – 0 point on Kelvin scale, the point at which all molecular movement stops.

Energy Energy-is the capacity to do work or produce heat.   The joule and the calorie are common units of energy. 1J=0.2390 cal 1cal = 4.184J

Density Density-is the ratio of the mass of an object to it volume   Density= mass Volume Density is an intensive property that depends only on the composition of a substance, not on the size of the sample. The density of a substance generally decreases as temperature increases Why? The volume usually increases as temperature increases. Therefore, making the denominator of the density formula larger and causing the density to be smaller.