Density of water at varies temperature'

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Density of water at varies temperature.
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Exercise
A chemist trying to identify the main compo- nent
of a disc cleaning fluid, finds that 25.00 cm3 of
substance has a mass of 19.625 g at 25 oC. The
following are the names and densit ies of the
compounds that might be the main component
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Compound D (g/cm3) at 25 oC Chloroform 1.492 D
iethyl ether 0.714 Ethanol 0.789 Isopropyl
alcohol 0.785 Toluene 0.867
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Significant Figures
Number of significant figures in a physical
quantity refers to the number of digits
reported for the value of a measured or
calculated quantity, indicating the precision of
the value.
Number of significant figures in a physical
quantity is the number of digits that are known
to be accurate plus one more.
Example mass of an object is 3.004 g
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Rules governing significant figures
1. Starting with the first nonzero digit on the
left, count this digit and all the remaining
digits to the right. This is the number of S.F.
in the measurement. 400,005 g and 400.005 g
0.045 mL , 0.0045 mL, and 0.00045 mL
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Rules governing significant figures
2. The number of S.F. is uncertain in number that
ends with zero. e.x. 1300 g
1.3 x 103 g
1.30 x 103 g
1.300 x 103 g
2 S.F 3 S.F 4 S.F
Example 4,500,000
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Scientific Notation
is a presentation of number in the form A X 10n
where A is a number with single nonzero digit to
the left of the point and n is an integer or
whole number integer, or whole number.
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Scientific Notation
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Exercise
How many significant figures are there in each
of the following measur- ements ? a. 73.0570
g b. 0.403 kg d. 3.50 x 10-3 m e.
0.0738 g c. 0.80190 m f. 1340.0 kg
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Uncertainty in Calculated Result
The mass of a beaker was found to be 43.82 g. The
same beaker containing water was found to have
mass 68.21 g. a. what is the mass of
water? b. what is uncertainty in this value?
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Rules for rounding calculated results
1. When we multiply or divide quantities, the
result is allowed no more significant
figures than carried by the least certain
quantity. 2. When we added or subtract numbers,
the result is allowed no more decimal
places than are in the number having the fewest
decimal places. 3. When the first of the
digits to be removed by rounding is 5 or
higher, round the digit to its left upward by one
unit. Other- wise, drop it and all others
after it. 4. Treat the exact numbers as having
an infinite number of signifi- cant
figures.
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Examples
1. A floor is measured as 11.75 m long and 9.25
m wide. What is its area?
2. Samples of a medication having masses of 1.12
g, 5.1 g, and 0.1657 g are mixed. How
should the total mass of the resulting
sample be repor- ted?
3. 4.18 - 58.16 x (3.38 - 3.01)
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The Factor - Label Method in Calculations
In calculations involving physical quantities,
the units are multiplied or canceled as if they
were numbers.

• It takes the relationship between units stated
  as an equation,
• (such as 1 in. 2.54 cm), expresses the
  relationship in a form
• of a fraction, called a conversion factor, and
  then multiplies
• some given quantity by this conversion factor.

• In this multiplication, identical units are
  multiplied or canceled as if they were numbers.

• If the units that remain for the answer are
  right, then the calculation
• was correctly setup.

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Examples
1. Convert 5.65 in. into cm
2. How many grams are in 0.230 lb ? 1 lb
453.6 g
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1.55 Rewrite the following number according the
number of significant figure specified in each
part. Give your answer in scientific
notation. 199,898.9091 a. three b. four c.
five d. six e. nine