Chapter 1: Chemistry and Measurements

Week 1 (9/12 & 9/16) lecture covering topics of measurement, conversion, significant figures, density, and more

Units of measurement

• volume

  • metric - liter (L)

  • SI - cubic meter (m³)

• length

  • metric & SI - meter (m)

• mass

  • metric - gram (g)

  • SI - kilogram (kg)

• temperature

  • metric - degree Celsius (ºC)

  • SI - Kelvin (K)

• time

  • metric & SI - second (s)

SI (international system of units) is a modification of the metric system. 

There are other units, but these are the more commonly used in the world of chemistry. 

Conversion factors

Conversion factors show equivalent factors — the relationship between the units

The unit of the given value must match the unit of the value in the denominator to cancel out

Significant figures

1) Numbers 1 to 9 are all significant figures

2) Zeros

• If the value is less than 1, all zeroes BEFORE the first non-zero digit are NOT significant figures; between and the end of the decimal ARE significant figures

• If the value is greater than 1 and does NOT have a decimal point, all trailing zeros to the right end of the number are NOT significant figures. If it’s greater than 1 with a decimal point, all digits ARE significant figures.

Examples: 1) .000000218 = 3 SF

2) .000218010 = 6 SF

3) 21000 = 2 SF

4) 21000.1 = 6 SF

Rules for significant figures (math operations)

Multiplication & Division: answer should have the lowest number of significant figures

• Ex: 39.521 _{(5 SF)} * 10.1 _{(3 SF)} / 2.12 _{(3 SF)} = 188.284 — final answer: 188

Addition & Subtraction: answer should have the lowest digit after decimal place (only one digit)

• Ex: 31.9125 + 2.100 - 15.1 = 18.9125 — final answer: 18.9

Decimal notation → scientific notation

1. The decimal point must be after the first non-zero digit

2. Given # smaller than final # → 10^-x

3. Given # larger than final # → 10^{+x (no need to put the plus sign, just indicating that it would be a positive integer instead of negative)}

Ex: 267.52 → 2.6752 × 10²

→ When asked for the correct number of significant figures in a problem, focus only on the value with no exponent (highlighted).

Major exponential values to remember

kilo = 10³ (1 km)

mega = 10⁶ (1Mm)

giga = 10⁹ (1 Gm)

deci = 10^-1 (1 dm)

centi = 10^-2 (1 cm)

milli = 10^-3 (1 mm)

micro = 10^-6 (1 μm)

nano = 10^-9 (1 nm)

Density

Density = mass/volume → D = m/v

• Defined as the mass of a given volume; physical property of matter

• Mass - typically displayed in grams (g)

• Volume - typically displayed in cm³ (cubic centimeter) or mL (milliliter) depending on whether the substance is a solid or liquid

• 1 mL = 1 cm³, so they can be used as interconvertible units.

• If a substance is less dense than its conditions, then the substance will float. 

Specific gravity

The specific gravity of a liquid sample is compared to the density of water.

The density of water is 1 g/mL.

Specific gravity = Density of sample liquid (g/mL) / Density of water (g/mL)

• The units cancel out, so there is no unit for specific gravity.

Specific gravity can also be measured with a hydrometer.