CHEM 1A

Tuesday, January 17, 2023

Thursday, January 19, 2023

Chapter 1

Metrics, Measurements and Significant Figures

A. SI Units

1. Length: meter

2. Mass: gram

3. Time: seconds

4. Temperature: kelvin

5. Volume: liters

B. 1.61 km = 1 mile

A. A way to express very small or large numbers

B. Examples

1. 0.0035 = 3.5 10^-3

2. 2.65 10^-2 = 0.0265

A. Accuracy v. precision

1. Accuracy: how close the measurement is to the true value

2. Precision: how close the measurements are to each other

B. SigFig rules

1. All non-zero digits are significant

2. Zeroes between non-zero digits are significant

3. Zeroes on the left side of a first non-zero digit are not significant (e.g. 0.02 has 1 sigfig)

4. Zeroes at the end of a number are only significant if there is a decimal point (e.g. 2.0 has 2 sigfigs; 20 has 1 sigfig)

C. Examples

1. 5.07 has 3 sigfigs

2. 0.0000876 has 3 sigfigs

3. 1.3254 10^-6 has 5 sigfigs

4. 998.9877000 has 10 sigfigs

5. 0.000009830000 has 7 sigfigs

6. 200 has 1 sigfig

7. 1.23 10^3 has 3 sigfigs

8. 22 chairs has infinite sigfigs

a. An exact quanitity has infinite sigfigs

D. Examples

1. 0.0000876216 in 3 sigfigs = 8.76 10^-5

E. Sigfigs in calculations

1. Addition and subtraction: the result has the same number of decimal places as the least precise measurement involved in the calculation

2. Multiplication and division: the result is the same as the number with the fewest sigfigs involved in the calculation

3. Don't round intermediate values, only round the final value

A. Metric prefixes

1. More than one unit: Tetra (^12), Giga (^9), Mega (^6), kilo (^3)

2. Less than one unit: deci (^-1), centi (^-2), milli (^-3), micro (^-6), nano (^-9), pico (^-12), femto (^-15), atto (^-18)

3. Must memorize kilo-nano

B. Examples

1. 496 dL = 49.6 L

2. 36.53 g = 0.03653 kg

A. Two conversions to remember (rest are provided on exams)

1. 1 kg = 2.20 lbs

2. 2.54 cm = 1 in

B. Practice

1. 36.1 cm = 14.2 in

2. 52.3 kg = 115 lbs

C. Examples

1. 100 cm x 5.6 cm x 32 cm = 39 in x 2.2 in x 13 in = 1100 in^3

A. The last digit of a measurement must be estimated (uncertain)

1. E.g. 2.25 +/- 0.05 mL

A. Density equals mass over volume (D=m/v) (in g/mL)

1. 25 mL of rubbing alcohol is 19.6 g and has a density of? 16 g/mL

2. Cough syrup has a density of 1.20 g/mL and there is 10.0 mL present. How many grams are present? 12.0 g

3. A medication has a density of 1.28 g/mL and there is 2.01 g present. How many mL are present? 1.57 mL

A. Conversions

1. Kelvin = celsius + 273.15

a. 273.15 is a constant and therefore has infinite sigfigs

2. Celsius = (F-32)(9/5)

B. Example

1. Convert 4 K to celsius and fahrenheit. -269 C and -118 F