Structure 1.4 Counting particles by mass: The mole

relative atomic mass

relative atomic mass

the weighted average mass of one atom of an element relative to 1/12 the mass of an atom of carbon-12

Avogadro's constant

Number of particles in 1 mole = 6.022 × 10²³

mole

the SI unit of amount of substance (mol), avogadro's number of entities

elementary entity

particles like an atom, a molecule, an ion, en electron, or a specified group of particles

why does the relative atomic mass not have a unit?

it's a relative term, compares the mass of atoms against the same standards (carbon-12)

relative formula mass

The sum of the relative atomic masses in a compound

molar mass

the mass of one mole of a substance

empirical formula

the simplest whole number ratio of atoms in a compound

molecular fomula

the actual number of atoms (whole numbers) of each element present in a compound, a multiple of the empirical formula

hydrated salt

A salt that contains water of crystallisation

water of crystallization

compounds containg a fixed ratio of water molecules

anhydrous salt

A salt which contains no water of crystallisation

combustion analysis

a method of obtaining empirical formulas for unknown compounds, especially those containing carbon and hydrogen

solution

A homogeneous mixture of two or more substances

solvent

the more abudant component of solutions (usually liquid)

solute

the less abundant component of solutions (dissolves into the solvent)

solid-solid solution example

metal alloys

solid-liquid solution example

salt water (aq)

liquid-liquid solution examples

vinegar, wine (ethanol and water)

gas-liquid solution example

fizzy drinks (carbon dioxide and water)

molar concentration

the amount of solute (moles) per volume of solution

What do square brackets mean?

concentration of

standard solution (stock solution)

a solution whose concentration is accurately known

ppm

parts per million

dilution

Adding water to a solution in order to decrease the concentration

serial dilution

a series of dilutions of a standard solution

Why are serial dilutions used?

diluting standard solutions to get smaller concentrations by adding solvent is more accurate than measuring small amount of solute on a balance (uncertainty with really small masses)

Ultraviolet-Visible Spectroscopy

a technique used to link the concentration of a sample (serial dilution) to its absorbance

why is the concentration of a sample directly proportional to its absorbance?

the colour of the sample fades gradually in serial dilution, decreasing concentration >> the amount of light absorbed decreases as well

calibration curve

A graph showing the value of some property versus concentration of analyte. When the corresponding property of an unknown is measured, its concentration can be determined from the graph. concentration vs. absorbance

are the concentration and absorbance of a sample directly proportional at all concentrations?

no, directly proportional at lower concentrations (a linear graph), not directly proportional at higher concentrations (a curve In the graph)

Titration

an experimental technique to determine the concentration of an unknown solution

Avogadro's law

equal volumes of all gases, at the same temperature and pressure, contain an equal number of particles

what kind of gases is the Avogadro's law for?

ideal gases