Chemistry 1.5, 1.6, ....
SI units
International System of Units
SI-English Conversions
Length Mass 1 m = 39.37 in 1 kg = 2.2046 lb 2.54 cm = 1 in (exact) 453.6 g = 1 lb 1.609 km = 1 mi. 28.35 g = 1 oz = 1760 yd 1 metric ton = = 5280 ft 2204.5 lb Volume 1 L = 1.057 qt 29.57 mL = 1 fl oz 3.785 L = 1 U.S. gal 0.473 L = 1 U.S. pint
The PRECISION is the closeness of all of a set of...
MEASURED values to ONE ANOTHER
Experiments that determine the amount of a substance present are
QUANTITATIVE MEASUREMENTS.
Scientists have agreed on a set of international standard units for comparing all our measurements called the...
SI Units.
SI Derived Units
a unit derived by combining SI base units
Determine which of the following values are given in SI base units, SI derived units or English units. a) 1.5 gal b) 2.04 kg * m/s^2 c) 298 K d) 8.25 s ^ -1
a) SI English units b) SI derived units c) SI base units d) SI derived units
Rules for Significant Figures 1) Does it have a decimal? = YES
- all the digits in the coefficient of a number in scientific notation are significant - all numbers can be expressed in scientific notation. You must only write the significant digits when using scientific notation. - Scientific notation ALWAYS has one number and then a decimal. All number written in scientific notation are significant. > 1.2345 = 1.2345 x 10^0 5 sig fig > 0.0123 = 1.23 x 10^-2. 3 sig fig > 0.001230 = 1.230 x 10^-3 4 sig fig > 0.010203 = 1.0203 x 10^-2 5 sig fig > 0.01020300 = 1.020300 x 10^-2 7 sig fig
Rules for Significant Figures 1. Does it have a decimal? = NO
- any zeros the right of all nonzero digits in an integer, such as in 4,000, are uncertain unless further information is given; 4000 has only one significant digit. > 4100 has 2 sig figs > 4110 has 3 sig figs > 4111 has 4 sig figs - To make a zero in an integer significant, it is best to write the number in scientific notation. - 4o00 = 4 x 10^3 - 4oo0 = 4.0 x 10^3 - 4ooo = 4.00 x 10^3 - 4000 = 4.000 x 10^3 or can also write 4000. (with decimal at the end).
Significant digits in calculated results: multiplication and division
- for multiplication and division, the number of significant digits in the measurements with the fewest significant digits limits the number of significant digits in the answer: 4.1 cm x 21.07 cm = 86.387 cm^2 = 86 cm^2 - the answer is rounded to the fewest number of SIGNIFICANT FIGURES that are present in the multiplied or divided values.
Significant Digits
- scientists report the precision of their measurements EVERYTIME they write down a result. - the number of digits they use consists of the absolutely certain digits plus one estimated digit. - every digit that reflects the precision of the measurement, including the estimated digit at the end, is called a significant digit or significant figure.
Significant digits in calculated results: addition & subtraction
- these calculations (+ and -) are the ones to watch out for. - they make finding the proper number of significant digits difficult. - calculator answers must be rounded to the correct number of significant digits. - in addition and subtraction, the last digit retained is the estimated digit furthest to the left in the measurements. - the answer is rounded to the fewest number of decimal places present in the values.
What is the best answer to the following expression: (4.9800 - 4.9680) x 0.2500?
0.0(120) x 0.2500 = 0.00(300)
Length is...
1 dimensional
In chemistry, QUALITATIVE DESCRIPTIONS refer to...
the identity or form of a substance present.
Which is larger: 1 mg or 1 Mg?
1 mg = 0.001g 1 Mg = 1,000,000 g so... Mg
Rules for significant figures 1. Does it have a decimal? = YES
1. All NONZERO numbers are significant 1.2345 o.o123 2. Any zeros to the LEFT of all NONZERO digits are NOT significant; o.o3 contains only one significant digit. o.oo1230 It is like reading from left to right. Start counting sig figs at FIRST nonzero number. This ONLY applies if it has a decimal. 3. Any zeros BETWEEN significant digits are significant; 903 contains three significant digits. 4. Any zeros to the RIGHT of all nonzero digits in a number with decimal-place digits are significant; 70.00 contains four significant digits. o.o1020300
Significant figures with addition and/or subtraction
1. do the calculation on your calculator 2. your calculator doesn't know how to do sig figs. You must work at this 3. the LEFTMOST significant # dictates where to look for number of sig figs. after you have finished calculation. 4. Round your answer to the correct decimal place. 29.865 g - 29.789 = 0.076 g (2 sig figs to 3rd decimal place) 29.865 g - 29.8 g = 0.1 g (1 sig fig to 1st decimal place) 29.865 g - 29.79 g = 0.08 g (1 sig fig to 2nd decimal place) 30 g - 2.9 g= 30 g (1 sig fig to the 'tens' place)
How many significant figures should be reported for the difference between 235.2497 and 235.22?
235.2497 - 235.22 = 0.(02)97 = 0.03
Round 1.23(4)5 to THREE significant digits.
> look at the leftmost digit to be dropped (shown here underlined = 4) >Is this number 5 or greater? > YES = add 1 to the # before it (here the number 3) > NO = leave the number alone ------> rounding yields the correct answer to be 1.23 to 3 sig figs.
Example 2: Round 1.23(5)4 to three significant digits
> look at the leftmost digit to be dropped (shown here underlined = 5) > is this number 5 or greater? > YES = add one to the # before it (here the number 3) > NO = leave the number alone -------> rounding yields the correct answer to be 1.24 to three sig figs.
Calculate the sum of 10.10 cm + 1.332 cm + 6.4 cm. Report the answer with the correct number of significant digits.
??
Underline the significant digits in each of the following measurements. A. 0.0020 m B. 1.200 m C. 10.002 m D. 6000 m
A. 0.00(20) B. 1.200 C. 10.002 D. (6)000 The 6 is significant because all nonzero digits are significant. The zeros to the right of all other digits in an integer are uncertain; they may reflect the precision or just the magnitude of the number. Without further information, it is impossible to tell (rule 4), so you would conclude that they are not significant.
Suppose a bathroom scale registers 2 lb with no load. An object is weighed repeatedly on this bathroom scale, and each results in a reading of 117 lb. A: Are the measurements precise? B:Are the measurements accurate? c: What is the probable true weight of the object?
A: The measurements are precise because exactly the same weight value (to the precision of the device) was obtained each time. B: They are not accurate because the no-load value was incorrect. C: Since the scale reads 2 lb with no load, it is likely giving readings that are falsely high by 2 lb. Therefore, the true weight is probably 117 lb - 2 lb = 115 lb.
SI prefixes
All units in the SI system are related to the standard unit by a power of 10. THESE YOU HAVE TO MEMORIZE!! Meter example for each: mega - M ---> 1,000,000 ---> 1 Mm = 10^6 m kilo - k ---> 1,000 ---> 1 km = 10^3 m deci - d ---> 0.1 ---> 10^1 dm = 1 m centi - c ---> 0.01 ---> 10^2 cm = 1 m milli - m ---> 0.001 ---> 10^3 mm = 1 m micro - u or mc ---> 0.000001 ---> 10^6 um = 1 m nano - n ---> 0.000000001 ---> 10^9 nm = 1 m pico - p ---> 0.000000000001 ---> 10^12 pm = 1
Perform the following calculations and report the answer to the correct number of significant digits. a. 2.171 cm x 4.20 cm b. 4.92 g / 1.64 cm^3
a. 2.171 cm x 4.20 cm = 9.1182 cm^2 (3 sig figs since that's smallest amount) answer: 9.12 cm^2 b. 4.92 g / 1.64 cm^3 = 3.00 g/cm^3
Find the result of each of the following calculations to the proper number of significant digits. a. 80.21 g - 79.93 g / 65.22 cm^3 b. (92.12 mL)(0.912 g/mL) + 223.02 g
a. 80.21 g - 79.93 g = 0.28 g 0.28 g / 65.22 cm^3 = **0.0043 g / cm^3 b. (92.12 mL)(0.912 g / mL) = 84.01344 84.01344 + 223.02 g = **307.0 g
SI-derived units are the products or powers of one or more...
base units. SI-derived units include units of area, volume, speed, and acceleration.
The radius of a circle is 13.7 cm. Calculate the diameter of the circle to the correct number of significant digits.
d = 2r 2 (13.7 cm) = **27.4 cm
SI prefixes can be added to a unit to...
describe a very large or very small measurement. The prefixes differ by powers of 10.
Different tools yield...
different levels of precision - if there is a digital readout; always reported all decimals.
Exact numbers....
don't limit the number of significant figures in a calculated result. - exact numbers include the following: > numbers that are definitions and not measurements, such as the number of centimeters in a meter (100) > counted items, such as the number of students in a classroom. > integers within formulas, such as the 2 in d = 2r
English-metric conversions are presented in this book only to...
give you an idea of the size of the metric unit. English units are rarely used in a chem lab.
The standard units of measurement in chemistry are the....
international system of units, SI units
Precision in single measurements is determined by the...
measuring device used.
There are 7 SI base units, and the ones most often in chemistry are the...
meter (length) kilogram (mass) second (time) kelvin (temperature) mole (amount of substance)
The rules for significant digits in addition and subtraction are different from those in....
multiplication and division.
Significant digits and decimal - place digits (such as the tenths place and hundredths place) are..
not the same. There is no necessary relationship between the two.
When making a measurement that has to be read from a scale, always estimate to...
one digit beyond the smallest scale division on the tool, if possible.
Measurements make identifications of substances more....
precise and enable more scientific generations to be made.
In general, calculators don't give the...
proper number of significant digits.
The precision that was used to make a measurement is....
reflected in the number of significant digits reported.
All the digits in the coefficient of a number in science notation are...
significant.
Scientific measurements are usually repeated 3 or more times because....
the average value of the measurements is probably closer to the true value than any individual measurement.
The ACCURACY is...
the closeness of the average of a set of measurements to the TRUE VALUE.
Volume is...
three dimensional - the volume of a rectangular pyramid = length x width x height
Area is...
two dimensional - the area of a square or rectangle = length x width
