GenChem Lesson 1

precision

how close the measurements in a series are to each other

measured w/ standard deviation

accuracy

how close each measurement is to the actual value

measured by percentage error

systematic error

produces values that’re either all higher or all lower than the actual value

predictable

happen all of the time

systematic error example

forgetting to sero a scale leads to low accuracy

random error

produces values that’re both higher and lower than the actual value

measured values’re inconsistent when repeated measures are taken

need to recheck everything

inaccurate

reliability

measurements are consistent

implies consistency but not accuracy

validity

measurements are accurate

implies accuracy of measurement

outliers

removed from the set of trials bcs they lack precision and accuracy

weighing by difference

used when triple beam balance is utilized

taring

act of setting a scale to zero to exclude a container's weight before measuring contents (tare weight)

used when an analytical balance is utilized

Metric System

from France

“Metric” = to measure

Prefixes on the measurement [Multipliers of 10 > (Greek); Multipliers of 10 < (Latin)]

international conference held to standardize the metric System in 1960

The International System of Unit (SI system) or “Le Systeme Internationale de Unites”

english system

aka Imperial Units (since the measurements were based off of English royalty)

makes use of conversion ratio or unit factor

conversion ratio

always = to 1

ratio of equivalent quantities used to express a quantity in different units

chosen and set up so that all units cancel except those required for the answer

remember when calculating

290. (3sf) ≠ 290 (2sf)

temperature

Measure of the average kinetic energy of the particles in an object

increase in temp = increase in motion of particles

standard unit: Kelvin (from SI system)

^oC → ^oF

^oF = (1.8) ^oC + 32

^oF → ^oC

^oC = (^oF-32) / 1.8

^oC → K

K = ^oC + 273.15

kelvin has no degree symbol

density

at a given temp and pressure, the a substance’s density is a characteristic physical property w/ a specific value

d=mass(g)/volume(mL, cc, or cm³)

densities of gasses’re lower than solids and liquids

Density of water

1 g/mL or 1 g/cm³

water displacement method

used to get the Volume of irregular solids

V_f - V_i = Volume of the irregular solid

always get the mass of the object first before putting it in the water

specific gravity

tells how many times a material is heavier or lighter compared to the reference material

ratio of the density of a substance to the density of water

one of the few unitless quantities in chemistry

specific gravity formula

sp gr = d_sample/d_water