chemistry basics Flashcards
describe an experiment for diffusion
potassium manganate (Vll) and water
- the purple pm slowly spreads out to fill the beaker- the pm particles are diffusing out among the water particles
- it’s the random motion of particles in a liquid that causes the purple colour to eventually be evenly spread out
what is dilution?
add more water to solution and the particles will spread further part creating a less concentrated solution
describe the ammonia and hydrogen chloride experiment
- aqueous ammonia (NH3) gives off ammonia gas. HCL gives off hydrogen chloride gas
- form a white ring of ammonium chloride in the glass tube
- the NH3 diffuses from one end and HCl from the other
- the ring forms nearer HCl because the particles of ammonia are smaller and lighter so diffuse through the air more quickly
what does the nucleus contain?
protons and neutrons
why is the overall charge positive?
because protons are positive
what are molecules?
groups of atoms joined together- some made of one element- some made up of more than one
how are molecules held together?
by covalent bonds
how do you seperate rock salt?
1) grinding- with pestel and mortar
2) dissolve in water and stir
3) filter- sand through filter paper in a funnel
4) crystalise - evaporate water in an evaporating dish
how does simple distillation work?
separating out a liquid from a solution
1) solution is heated, the part of the solution with lowest boiling point evaporates
2) the vapour is cooled, condenses and is collected
3) the rest is left in the flask
4) use for seawater- the water evaporates and is condenses and collected- end up with just salt at the bottom
5) only useful for separating things with very different boiling points
how does fractional distillation work?
for a mixture of liquids
1) put mixture in flask with fractionating column on top and heat
2) the liquid with lowest boiling point evaporates first and when the temperature on the thermometer matches the boiling point of this liquids, it will reach the top of the column
3) liquids with higher boiling points might have evaporated too but as it is cooler towards the top of the column they will have condensed and run back down to the flask
4) when first liquid has been collected, you raise the temperature until the next one reaches the top
how does the periodic table show the elements?
in order of increasing atomic number
group 1 are called?
the alkali metals
group7 are called?
the halogens
group 0 are called?
the noble gases
what does the properties of elements depend on?
on the number of electrons they have in the outer shell
describe ionic bonding
atoms lose or gain electrons top form charged particles called ions which are then strongly attracted to one another- know as electrostatic attraction- high melting point and boiling point
what happens in covalent bonding?
atoms share pairs of electrons to have a full outer shell. there’s a strong attraction between the shared electrons and the nuclei of the atom
what’s the bonding like in simple molecular substances?
atoms within a molecule are held together by very strong covalent bonds but the forces of attraction between the molecules are very weak so as a result of these intermolecular forces- melting and boiling point are low-easily parted from eachother
most molecular substances are what at room temp?
gases of liquids
what are giant covalent structures like?
- similar to giant ionic but no charged ions
- all atoms are bonded by strong covalent bonds
- lots of bonds which means it takes a lot of energy to break them so have high melting and boiling points
- don’t conduct electricty
- usually insoluble in water
- diamond and graphite have giant covalent structures are both made from only carbon
