1) Principles of chemistry Flashcards
Three states of matter
-solids
-liquids
-gases
Solid characteristics
-very close together
-regular pattern
-vibrate around a fixed point
-low energy
Liquid characteristics
-particles are close
-randomly arranged
-move around each other
-higher energy
Gas characteristics
-widely spaced
-randomly arranged
-move quickly in all directions
-highest energy
Interconversions between states of matter - heating up
Solid –melting–> liquid –boiling/evaporation–> gas
solid –sublimation–> gas
Interconversions between states of matter - cooling down
gas –condensing–> liquid –freezing–> solid
gas –deposition–> solid
Boiling vs evaporation
-at boiling point - all particles have enough energy
-at lower temperature - only surface particles have enough energy
Practical: dilution of coloured solutions
- When potassium manganate (VII) crystals are dissolved in water, a purple solution is formed
- A small number of crystals produce a highly intense colour
Dissolving potassium manganate (VII) explanation
Water and dye are moving randomly and particles can slide over each other
-particles can easily mix together
-diffusion in liquids is slower than in gases because the particles in a liquid are closely packed together and move more slowly
Practical: diffusion of gases
-When ammonium gas and hydrogen chloride gas mix, they react together to form a white solid - ammonium chloride
1. A cotton wool pad was soaked in ammonia solution and another in hydrogen chloride solution
2. Two pads put into opposite ends of a dry glass tube at the same time
Diffusion of ammonia gas and hydrogen chloride - explanation
-ring of ammonium chloride forms close to the hydrochloric acid end because ammonia particles are lighter than hydrogen chloride particles and therefore travel faster
-particles move in random directions and will collide with air particles in the tube
Solvent definition
The liquid in which a solute dissolves
Solute definition
The substance which dissolves in a liquid to form a solution
Solution definition
The mixture formed when a solute is dissolved in a solvent
Saturated solution definition
A solution with the maximum concentration of solute dissolved in the solvent
Soluble definition
Describes a substance that will dissolve
Insoluble definition
Describes a substance that won’t dissolve
Solubility definition
A measurement of how much a substance will dissolve in a given volume of a liquid
-g of solute per 100g of solvent
Solubility of gases - temperature and pressure
Pressure increases, gases become more soluble
Temperature increases, gases become less soluble
Solubility curves
Solubility (g of solute per 100g) - y-axis
Temperature - x-axis
Practical: Investigate the Solubility of a Solid in Water at a Specific Temperature
- Pour deionised water into a 250 cm3 beaker
- Use a water bath to heat to desired temperature
- Add known masses of the solid bit by bit until solution is saturated
- Record the mass of solid that was soluble.
- Repeat steps 1-4 with the water at different temperatures
Element definition
A substance made up of atoms that all contains the same number of protons and cannot be split into anything simpler
Compound definition
A substance formed when two or more elements are chemically bonded together. Cannot be separated by physical means
Mixture definition
Two or more substances that are not chemically bonded together. Can be separated by physical means
Pure substance - cooling curve
-horizontal line where the compound has a sharp melting point
-is a pure substance as they melt and boil at specific and sharp temperatures
Impure substance - cooling curve
-produce a gradual decrease in temperature
-mixtures have a range of melting and boiling points as they consist of different substances that tend to lower the melting point and broaden the melting point range
Different separation techniques
-simple distillation
-fractional distillation
-filtration
-crystallisation
-paper chromatography
Simple distillation
-used to separate a liquid and soluble solid from a solution or a pure liquid from a mixture of liquids
1. The solution is heated, and pure water evaporates producing a vapour
2. The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker
3. After all the water is evaporated from the solution, only the solid solute will be left behind
Fractional distillation
-Used to separate a mixture of different liquids that have different (but very similar) boiling points
1. The solution is heated to the temperature of the substance with the lowest boiling point
2. This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
3. All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
Fractional distillation - fractionating column
-fractionating column is full of little glass rod - large surface area
-evaporating substance comes into contact with glass rods, which are cooler than their boiling point
-condense back into liquid form and fall back into the flash
-only pure methanol falls into the beaker
Filtration
Used to separate an undissolved solid from a solution
1. filter paper funnel above a beaker
2. A mixture poured
3. The filter paper allow small liquid particles to pass through
4. Solid particles are too large to pass stay behind as a residue
Crystallisation
Separate dissolved solid from a solution, when solid is much more soluble in hot solvent than cold
1. Heat solution, evaporate solvent, leave saturated solution behind
2. Test if saturated: dip clean, dry, cold glass rod into solution, crystals will form on the glass rod
3. cool solution slowly
4. Crystals begin to grow as solids will come out of solution due to decreasing solubility
6. filtering the solution, washed, dry
Paper chromatography
Technique is used to separate substances that have different solubilities in a given solvent
1. Take a piece of filter paper and use a pencil to draw a line at the bottom of the sheet - baseline
2. Add sample of ink to the pencil line
3. Add a shallow amount of solvent to a beaker
4. Put filter paper inside
5. Wait for solvent to seep up the paper. Different dyes in inks will dissolve in the solvent and move up in it
-different substances separate out
Calculate Rf value
Reference value - always the same value of a compound but dependent on the solvent used
-allows chemists to identify unknown substances by comparing Rf values of known substances under the same conditions
-between 0-1 - close to 1 - more soluble
distance travelled by substance/ distance travelled by solvent
Atom definition
Smallest particles of an element that consists of electrons surrounding a nucleus that contains protons and neutrons
Molecule definition
A group of two or more atoms chemically bonded together
Structure of the atom
-consists of a central nucleus
-composed of protons and neutrons
-surrounded by electrons
-atoms are neutral as the number of electrons and protons are equal
Proton - mass and charge
Mass: 1
Change: +1
Neutron - mass and charge
Mass: 1
Change: 0
Electron - mass and charge
Mass: negligible (1/1836)
Charge: -1
Atomic number definition
The number of protons in the nucleus of an atom
Mass number definition
The sum of the number of protons and neutrons in the nucleus of an atom
Isotopes definition
Atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
-same atomic number but different mass number
Relative atomic mass definition (Ar)
Weighted average mass of the isotopes of an element relative to the mass of 1/12th of a carbon-12 atom
Calculate relative atomic mass
[(% of isotope A x mass of isotope A) + (% of isotope B x mass of isotope B)]/ 100
Periodic table - periods
Horizontal rows that show the number of shells of electrons an atom has and are numbered from 1-7
Periodic table - groups
Vertical columns that show how many outer electrons each atom has and are numbered from 1-7
-final group is called group 0 - noble gases - full outer shell
Electron configuration
-electrons orbit the nucleus in shells
-further away from the nucleus, more energy a shell has
-first shell: 2 electrons
-second, third shell: 8 electrons each
-outmost shell: valence shell
–an atom is much more stable if the outer shell is full
–if shell is not full, atoms react with other atoms to achieve a full outer shell of electrons or lose electrons to empty the shell
Metal vs nonmetal - conductivity
Metal - good conductors of electricity
Nonmetal - poor conductors of electricity
Metal vs nonmetal - acid-base character of oxides
Metal - oxides that are basic - react with acids to give salt and water
Nonmetal - have oxides which are acidic or neutral
Identify a metal/ non metal on the periodic table
-search up periodic table
Elements with similar chemical properties
-same group in the periodic table
-as they have the same number of outer electrons so will react and bond similarly
Noble gases
-elements in group 0
-have full outer shells - extremely stable
-unreactive and inert
Noble gas characteristics
-all non-metal
-monatomic (exist as single atoms)
-colourless
-non flammable gases at room temperature
Ionic equations
-in aqueous solutions, ionic compounds dissociate into their ions
-separate into component ions that formed them
-e.g. HCl (aq) → H+ (aq) + Cl-(aq)
Relative formula mass (Mr)
Mass of a molecule or compound
-calculated by adding up the relative atomic masses (Ar) of all the atoms present in the formula
-molar mass
Calculating percentage by mass of an element in a compound
[(Ar x number of atoms of the element) / Mr of the compound] x 100
Mole definition
The unit for the amount of substance
Avogadro constant
Number of atoms/ molecules/ ions in a mole of a given substance
-6.02 x 10^23 per mole
e.g. one mole of Na contains 6.02 x 10^23 atoms of sodium
Moles - mass calculations
mass = mole x Mr
Calculate reacting masses
- Write balanced equation
- Fill in mass you know and ? mass you need
- Write down Mr
- Calculate mol from mass/Mr
- Compare molar ratio from equation to find other moles
- Find mass
Calculate percentage yield
(actual yield/ theoretical yield) x 100
Empirical formula
Shows the simplest whole number ratio between atoms/ ions in a compound
Molecular formula
Formula that shows the number and type of each atom in a molecule
Calculate molecular formula from empirical formula
- Calculate relative mass of empirical formula
- Divide actual relative mass by mass above
- Equals how many times bigger the molecular formula is compared to the empirical formula
Calculate empirical formula
- List the symbol for each element
- Write down the masses for each element
- Divide by their relative atomic mass
- Divide all numbers by the smallest of these numbers to get a ratio
- Should be 1:__
Calculating concentrations of solutions
moles = concentration x volume (dm3)
Avogadro’s law
At same conditions of temp and pressure, equal amounts of gases occupy the same volume of space
-one mole of gas is 24dm3
-molar gas volume at RTP (room temp and pressure - 20C and 1atm)
