scientific measurment chem

Why do scientists use standard units?

To ensure measurements are consistent, accurate, and understood worldwide.

What system of measurement is used worldwide?

SI (International System of Units)

What is qualitative data?

Describes descriptive qualities without numbers, such as color or texture.

What is quantitative data?

Describes how much or how many using numbers and units, such as 31^{\circ}C or 5 \text{ m}.

What is a quantity?

Something that can be measured, such as length, mass, or time.

What is a unit?

The specific scale in which a quantity is measured, such as \text{meter}, \text{kilogram}, or \text{liter}.

SI Base Unit: Length

\text{meter (m)}

SI Base Unit: Mass

\text{kilogram (kg)}

SI Base Unit: Time

\text{second (s)}

SI Base Unit: Temperature

\text{kelvin (K)}

SI Base Unit: Amount of substance

\text{mole (mol)}

SI Base Unit: Electric Current

\text{ampere (A)}

SI Base Unit: Luminous Intensity

\text{candela (cd)}

Symbol for distance

d

Symbol for mass

m

Symbol for time

t

Symbol for temperature

T

Symbol for amount of substance

n

Definition of Mass

The amount of matter in an object; it remains constant regardless of location.

Definition of Weight

The force of gravity exerted on an object; it changes depending on its location in the universe.

What are derived units?

Units formed by mathematically combining SI base units.

Volume formula and common units

V = L \times W \times H. Units include cubic meters (m^3) for solids or liters (L) for fluids.

Equivalence between solid and liquid volume

1 \text{ cm}^3 = 1 \text{ mL}

Density formula

D = m / V

Standard density units for solids

\text{g/cm}^3

Standard density units for liquids and gases

\text{g/mL} or \text{g/L}

Relationship between density and buoyancy

High density objects sink in a reference fluid; low density objects float.

Density Calculation: m = 100 \text{ g}, V = 5 \text{ cm}^3

D = 100 / 5 = 20 \text{ g/cm}^3

Calculate Mass: D = 7.9 \text{ g/cm}^3, dimensions 2 \times 5 \times 3 \text{ cm}

V = 30 \text{ cm}^3 \rightarrow m = 7.9 \times 30 = 237 \text{ g}

Calculate Volume: D = 3.12 \text{ g/mL}, m = 10 \text{ g}

V = 10 / 3.12 \approx 3.2 \text{ mL}

Scientific notation format

M \times 10^n, where M is a number between 1 and 9.

Meaning of a positive exponent in scientific notation

Indicates a large number where the decimal point has moved to the left.

Meaning of a negative exponent in scientific notation

Indicates a small number where the decimal point has moved to the right.

Convert 560,000 to scientific notation

5.60 \times 10^5

Convert 0.000004120 to scientific notation

4.120 \times 10^{-6}

Convert 7.05 \times 10^1 to ordinary notation

70.5

Convert 4.0920 \times 10^4 to ordinary notation

40,920

Multiplication rule for scientific notation

Multiply the coefficients (M values) and add the exponents (n values).

Division rule for scientific notation

Divide the coefficients (M values) and subtract the exponents (n values).

Addition and Subtraction rule for scientific notation

Exponents must be made equal before adding or subtracting the coefficients.

Calculate: (4.81 \times 10^4) \times (5.96 \times 10^9)

28.68 \times 10^{13} \rightarrow 2.868 \times 10^{14}

Metric conversion mnemonic

King Henry Died By Drinking Chocolate Milk (Kilo, Hecto, Deca, Base, Deci, Centi, Milli)

Prefix: kilo- (k)

Value: 10^3; move decimal 3 places to the left for base-to-kilo conversion.

Prefix: centi- (c)

Value: 10^{-2}; move decimal 2 places to the right for base-to-centi conversion.

Prefix: milli- (m)

Value: 10^{-3}; move decimal 3 places to the right for base-to-milli conversion.

Prefix: micro- (\mu)

Value: 10^{-6}; move decimal 6 places to the right for base-to-micro conversion.

Convert 6.3 \text{ mm} to \text{ cm}

0.63 \text{ cm}

Convert 15.8 \text{ cm} to \text{ mm}

158 \text{ mm}

Convert 0.185 \text{ L} to \text{ mL}

185 \text{ mL}

What is accuracy?

How close a specific measurement is to the true or accepted value.

What is precision?

How consistent or repeatable measurements are with each other.

Percent error formula

|\text{Actual} - \text{Experimental}| / \text{Actual} \times 100

Evaluate Quality: Student gets 7.39 \text{ g/cm}^3, actual is 8.94 \text{ g/cm}^3

\text{Percent Error} = |8.94 - 7.39| / 8.94 \times 100 \approx 17.34\%

Common factors affecting measurement quality

Human error, equipment limitations, environmental contamination, and improper calibration.

Kelvin to Celsius conversion formula

^{\circ}C = K - 273.15

Celsius to Kelvin conversion formula

K = ^{\circ}C + 273.15

Absolute Zero in Kelvin

0 \text{ K}

Common boiling point of water in Kelvin

373.15 \text{ K}

Prefix: Mega- (M)

Value: 10^6

Prefix: Giga- (G)

Value: 10^9

Prefix: Nano- (n)

Value: 10^{-9}

Prefix: Pico- (p)

Value: 10^{-12}

Symbol for Electric Current

I

Symbol for Luminous Intensity

I_v

Example of high precision and low accuracy

Hitting the same spot on a target repeatedly, but far away from the bullseye.

Example of high accuracy and high precision

Hitting the bullseye of a target repeatedly in the same spot.

Convert 1 \text{ kg} to grams (\text{g})

1,000 \text{ g}

Convert 500 \text{ mL} to liters (\text{L})

0.5 \text{ L}

Density of pure water at roughly 4^{\circ}C

1.0 \text{ g/mL}

Calculate Volume: m = 50 \text{ g}, D = 2 \text{ g/mL}

V = 25 \text{ mL}

Calculate Mass: V = 5 \text{ cm}^3, D = 4 \text{ g/cm}^3

20 \text{ g}

Writing 0.003 in scientific notation

3 \times 10^{-3}

Writing 8,900,000 in scientific notation

8.9 \times 10^6

Convert 1.2 \times 10^{-3} to ordinary notation

0.0012

Convert 3.5 \times 10^2 to ordinary notation

350

Symbol for Volume

V

Symbol for Density

D (or sometimes the Greek letter rho, \rho)

Calculate: (8 \times 10^6) / (2 \times 10^2)

4 \times 10^4

Decimal movement for kilo- to base

Move the decimal 3 places to the right.

Decimal movement for milli- to base

Move the decimal 3 places to the left.