Chemistry and Calculations

Chemistry and Calculations Chemistry Honors

Accuracy & Precision Precision: how closely individual measurements compare with each other Accuracy: how closely individual measurements compare with the true or accepted value

Accurate or Precise? • Ex: What is the temperature at which water boils? • Measurements: 95.0°C, 95.1°C, 95.3°C • True value: 100°C Precise! (but not too accurate)

Accurate or Precise? • Ex: What is the temperature at which water freezes? • Measurements: 0.2°C, 5.1°C, -5.0°C • True value: 0.0°C Accurate! (but not too precise)

Accurate or Precise? • Ex: What is the mass of one Liter of water? • Measurements: 1.000 kg, 0.999 kg, 1.002 kg • True value: 1.000 kg Accurate & Precise (it’s time to go pro)

Accurate or Precise? • Ex: What is the atmospheric pressure at sea level? • Measurements: 10.01 atm, 0.25 atm, 234.5 atm • True value: 1.00 atm Not Accurate & Not Precise (don’t quit your day job)

42.0 40 40.0 20 Uncertainty • To measure the time for a pencil tofall, compare a wall clock and a stopwatch. • To measure the volume of a liquid, compare a beaker and a graduated cylinder. 41. mL:One digit known (4) and one estimated (1). 42.1 mL:Two digits known (42) and one estimated (1).

The stopwatch and graduated cylinder… • Are more precise instruments (are more certain.) • Give measurements that are known to more decimal places. .

Significant Figures (“sig figs”): All the digits known with certainty plus one final digit, which is somewhat uncertain. In a correctly reported measured value, the final digit is significant but not certain. If the number 31.2 is reported. 3 & 1 are known with certainty, the 2 is significant but uncertain. A more precise instrument will give more sig figs in its measurement

PACIFIC PACIFIC When are digits “significant”? The “Atlantic-Pacific” Rule “PACIFIC” Decimal point is PRESENT. Count digits from left side, starting with the first nonzero digit. 40603.23 ft2 = 7 sig figs 0.01586 mL = 4 sig figs

ATLANTIC ATLANTIC When are digits “significant”? “ATLANTIC” Decimal point is ABSENT. Count digits from right side, starting with the first nonzero digit. 3 sig figs = 40600 ft2 1 sig fig = 1000 mL

Significant Figures 0.400030 On TheLeft! 6 On TheRight! Pacific Ocean Decimal Present! Atlantic Ocean Decimal Absent!

Significant Figures 1782156832 On TheLeft! 10 On TheRight! Pacific Ocean Decimal Present! Atlantic Ocean Decimal Absent!

Significant Figures 32710. On TheLeft! 5 On TheRight! Pacific Ocean Decimal Present! Atlantic Ocean Decimal Absent!

Examples • 0.00932 Decimal point present → “Pacific” → count digits from left, starting with first nonzero digit = 3 sig figs • 27510 Decimal point absent → “Atlantic” → count digits from right, starting with first nonzero digit = 4 sig figs • If number is obtained by counting, ex: 8 beakers, or is used in a conversion factor, ex: 1000 mm= 1 meter it is an exact number. = unlimited number of significant figures.

Significant Figures 32710. On TheLeft! 5 On TheRight! Pacific Ocean Decimal Present! Atlantic Ocean Decimal Absent!

Addition and Subtraction • The answer has the same number of digits to the right of the decimal point as there are in the measurement having the fewest digits to the right of the decimal point. • Ex: 56.31g – 14.1g = • Answer must be rounded so has only one number to the right of the decimal point.

Multiplication and Division • The answer has no more sig. figs. than are in the measurement with the fewest number of sig.figs. • 7.2 cm X 8.141 cm =58 cm2 The answer can only have 2 sig. Figs.

2.4: Scientific Notation How important is a change in the power of 10? Diameter of Earth’s orbit around the sun ≈ 100,000,000,000 m = 1.0*1011 m Diameter of an atom ≈ 0.0000000001 = 1.0*10-10 m Clearly show the # of sig figs in a a measurement

Writing in scientific notation 1. Move the decimal point in the original number so that it is located to the right of the first nonzero digit. 2. Multiply the new number by 10 raised to the proper power that is equal to the number of places the decimal moved. The form is M x 10n 3. If the decimal point moves: • To the left, the power of 10 is positive. • To the right, the power of 10 is negative.

Write the following measurements in scientific notation, then record the number of sig figs. • 789 g • 96,875 mL • 0.0000133 J • 8.915 atm • 0.94°C 3 sig figs 7.89*102 g 5 sig figs 9.6875*104 mL 1.33*10-5 J 3 sig figs 4 sig figs 8.915 *100 atm 2 sig figs 9.4*10-1 °C

When Adding & Subtracting • All values must have same exponent • Ex: 4.71 X 103 L+ 3.3 X 104 L = 4.71 X 103 L+ 33. X 103 L = 37.71 X 103 L OR .471X 104 L+ 03.3 X 104 L =3.771 X 104 L Answer = 3.8 X 104 L Convert answer to appropriate scientific notation. Least number of places past decimal

Multiplication & Division • Multiplication: the M factors are multiplied and the exponents are added Ex: (8.19 x 102 mm)(1.0 x 105 mm) = 8.2 x 107 mm2 when length units multiplied, answer units is area • Division:The M factors are divided, and the exponent of the denominator is subtracted from that of the numerator. Ex: 9.2 x 104 g = 9.2 g x 104-2 g/mL 4.55 x 102 mL 4.55 mL

Rounding Rules: round at the last step in a multistep process

Système International d'Unités • The metric system or Système International d'Unités (S.I.), was first organized in Paris as part of the French Revolution & adopted by France in 1795. At that time, the meter & kilogram were standardized. • Every country in the world uses SI units except the USA, Myanmar, & Liberia. • By 2009, all products sold in Europe must use the metric system. No dual-labeling will be permitted.

The Metric Prefixes

The Standard Units

More on S.I • The S.I. unit for volume is the cubic meter (m3). • The Liter,not S.I. Unit, is defined as a cube measuring 1 decimeter on each side, or 1 dm3, or 1000 cm3. • 1 cm3 = 1 mL. • The S.I. unit for mass is the kilogram, and is defined as the mass of 1 dm3 of water at 4°C. 1 dm 1dm 1 dm

What is a kelvin? • The S.I. unit for temperature is the kelvin, and is defined as 1/100 of the temperature difference between the boiling point & freezing point of water at one atmosphere of pressure. • The kelvin (K) and the degree Celsius (°C) are exactly the same size, although 1 degree Fahrenheit (°F)is equal to about 1.8°C. • To convert: • K = °C + 273.15 • °F = (1.8 * °C) + 32 • kelvin is based on water and absolute zero (the coldest temperature possible.)

What is density? • Density (d) is the ratio of the mass (m) of a substance divided by its volume (V). density = mass / volume • The most common units of density are: g/cm3 or g/mL. 1 cm3 = 1 mL • The density of water is 1.0 g/mL at 4.0 ° C 0.80 g/mL 1.0 g/mL 1.2 g/mL

Percent Error • Used to compare the accuracy of an individual or an average experimental value to the accepted value. Value acc – Value experimental X 100 Value acc • Ex: What is the % error for a measurement of 46.1 g, given that the correct value is 45.9g?

Direct Proportions • Equation Forms: OR

Indirect Proportions Equation Forms: OR

Dimensional Analysis • A method for converting units Example: A sample has a mass of 1245 g; how many kg is that? • Determine a conversion factor between the original units and the required units. __?__ kg = __?__ g Recall that k = 1000 = 103. • So, 1 kg = 1000 g or 10-3 kg = 1 g.

Change the conversion factor into a fraction. 1000 g or 1 kg1 kg 1000 g • Similar to 5 = 5, so 5 / 5 = 1 or10 = 10, so 10 / 10 = 1. You are creating a value equal to 1.

Chemistry and Calculations

Chemistry and Calculations

Presentation Transcript

HIGHER GRADE CHEMISTRY CALCULATIONS

STANDARD GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

Chemistry Calculations

Calculations in Chemistry

Calculations in Chemistry

Additional Chemistry Calculations

Mineral Chemistry Calculations

Calculations in Chemistry

Calculations in Chemistry:

HIGHER GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

HIGHER GRADE CHEMISTRY CALCULATIONS

Calculations in Chemistry

Calculations in Chemistry