AS and Periodic table Flashcards
What is meant by an atom?
An atom is the smallest part of an element that can exist.
What is meant by an element?
A substance that consists of only one type of atom.
What is meant by a compound?
A substance composed of two or more different elements chemically bonded together in fixed proportions.
What is meant by a mixture?
Two or more substances not chemically bonded together.
What is meant by a molecule?
2 or more different or same elements chemically bonded together.
Describe the properties of compounds in comparison to they elements it’s made from?
- Properties of compounds are different to properties of the elements they are made from.
Describe the properties of mixtures in comparison to the elements they are made from.
The properties of a mixture are the same as that of the elements they are made from. The properties are unchanged.
How can compounds be separated?
Through chemical reactions
How can mixtures be separated?
Through physical separation processes
How are compounds formed?
From chemical reactions.
What 2 things do chemical reactions always involve
- The formation of new substances
- A detectable energy change
What is filtration used to separate?
Insoluble solids from liquids.
eg X(s) from Y(l)
Summarise the process of filtration
- Place filter paper in filter funnel
- Put filter paper and funnel in a conical flask
- Pour the mixture into the filter paper
- The filter paper contains pores that allow liquid to pass through
- The insoluble solid will remain in the filter paper as it can’t pass through the pores, this is called the residue.
- The liquid will pass through the filter paper pores into the conical flask, and this is called the filtrate.
Give an example of filtration:
Filtering rock from water
What is crystallisation used to separate?
Soluble solids from liquids.
eg X(aq) from Y(l)
Summarise how crystallisation works:
- Leave solution in apparatus such as beaker for a few days.
- Water(or any liquid) evaporates
- Leaving behind crystals of solid substance that was once dissolved in the liquid.
OR
- Place solution in evaporating dish
- Heat evaporating dish GENTLY on Bunsen burner flame for water/liquid to evaporate
- This leaves behind crystals of the solid substance that was once dissolved in the liquid.
Why do scientists prefer evaporation over a few days rather than with a Bunsen burner during crystallisation?
- Because with a bunsen burner some chemicals break down due to heat (thermal decomposition).
- This effects the properties of the solid crystal produced (they will change).
Give an example of crystallisation:
Sodium chloride,NaCl, from salt water.
(salt from salt water to make salt crystals).
What is simple distillation used for?
To separate a dissolved solid from a liquid while also keeping the liquid.
What 2 main processes does simple distillation include, to obtain the liquid?
- Evaporation of liquid by heating.
- Condensation of liquid by cooling.
Describe the set-up for simple distillation.
- Flask connected to continuous glass tube
- Beaker at the end of continuous glass to collect liquid
- Glass tube is surrounded by a condenser that keeps the internal glass tube cold
- Cold water continuously runs in and out of the condenser
- Thermometer is also part of the apparatus
(Look at image).
Example of what simple distillation can be used for.
Production of drinking water from sea water.
A lot of energy is required from simple distillation so other techniques are used to do this.
Why is simple distillation not commonly used to provide drinking water from sea water?
A lot of energy is required from simple distillation so other techniques are used.
Explain the process of simple distillation.
- Solution is heated in a flask using a Bunsen burner until it boils.
- Liquid evaporates and turns into vapour.
- Vapour rises and as it rises the thermometer reading increases.
- Vapour passes into the continuous internal tube that is surrounded by a condenser.
- The condenser is cold bc tap water is continuously circulating around it.
- This causes the vapour to condense to a liquid
- The liquid is passed into the beaker
- And we are left with solid crystals in the flask and liquid in the beaker.
What is fractional distillation used to separate?
- A mixture of different liquids with different boiling points, from each other.
Example of simple distillation?
Separating seawater from salt to keep salt and sea water.
Example of fractional distillation?
Separating crude oil into diff hydrocarbon chain lengths.
or
Water from vinegar
What does the set up of fractional distillation have that simple distillation doesn’t?
A fractionating column containing glass beads.
Explain the process of fractional distillation.
- Start by gently heating the liquids in the flask using a bunsen burner
- Liquids will begin to evaporate to form a vapour, but the liquid with the lower boiling point evaporates more easily.
- As the mixture of vapours rise, they reach the fractionating column.
- There, the condense and drip back into the flask where they evaporate again.
- The repeated condensation and evaporation increases the amount of the lower BP liquid vapour in the fractionating column.
- So eventually the vapour of the lower BP liquid will travel ahead of that of the higher BP liquid in the fractionating column.
- So the thermometer reading will increase to show a mixture of vapours is passing through.
- Vapours pass into the condenser and condense into the beaker.
- This is still a mixture of liquids but mainly the lower BP liquid.
- This process continues until the temperature on the thermometer reading stops rising and reaches a constant temperature, the vapour sample is relatively pure.
- This shows that only the vapour of the lower BP liquid is passing thru.
- Now we collect this liquid in a fresh beaker.
- After some time the temperature of thermometer reading will begin to rise again until it reaches a constant temperature.
- Bc vapour of higher BP is passing over it.
- This will condense - collect this in another fresh beaker.
^^NOT USEFUL FOR LARGE VOLUME EG CRUDE OIL
If the two liquids in fractional distillation have a VERY similar boiling point, what should we do and why?
- It will be harder to separate these liquids so
- Carry out several rounds of fractional distillation
Chromatography
Look at other flashcards
State 1 way a scientific model could be replaced or changed?
If new experimental evidence is proposed/released.
Explain how the modern nuclear model of the atom came about.
- Ancient greeks believed atoms were tiny spheres that couldn’t be divided.
- Then the electron was discovered leading to the Plum Pudding Model of the atom; atom is a ball of positive charge w negative electrons embedded within it, by JJ Thompson.
- Scientists wanted to see if PPM is true so conducted the Alpha Scattering Experiment
- They fired tiny alpha particles at gold foil from an alpha particle source.
- Alpha particles have a positive charge, and gold foil was used bc it can be hammered to a few cm thick.
OBSERVATIONS + CONCLUSIONS - Most alpha particles passed straight thru gold foil w no change in direction; atoms are mainly empty space (PPM = wrong)
- some alpha particles deflected; centre of atom/nucleus = positive charge bc + alpha particles were repelled (PPM = wrong)
- sometimes alpha particles bounced straight back; mass of atom concentrated in the centre of it/nucleus. (PPM = wrong)
- Then, after carrying out calculations which experimental data supported, Bohr discovered that electrons orbit the nucleus at specific distances called energy levels, this meant the alpha scattering = wrong bc suggested they were all at one level.
- Later experiments showed that the positive charge of the nucleus could be divided into a WHOLE number of smaller particles which each have the same amount of positive charge, these are called protons.
- Then Chadwick provided evidence for the existence of neutrons (this idea was alr accepted for abt 20 yrs)
Why did the new evidence from the scattering experiment lead to a change in the atomic model
- Alpha particles have a positive charge, and gold foil was used bc it can be hammered to a few cm thick.
OBSERVATIONS + CONCLUSIONS - Most alpha particles passed straight thru gold foil w no change in direction; atoms are mainly empty space (PPM = wrong, bc it said that ball of positive charge with negative electrons embedded within it)
- some alpha particles deflected; centre of atom/nucleus = positive charge bc + alpha particles were repelled (PPM = wrong bc it said atom was ball of + charge, this says + charge is ONLY in centre)
- sometimes alpha particles bounced straight back; mass of atom concentrated in the centre of it/nucleus. (PPM = wrong, bc PPM suggest mass is everywhere, and that mass isn’t concentrated in nucleus, it doesn’t acknowledge one)
Describe the differences between the plum pudding model of the atom and the nuclear model of the atom (4 marks)
- PPM atom mass spread evenly throughout NM mass is concentrated in the centre.
- PPM negative electrons are embedded within atom uniformly, NM negative electrons are found at the edge of the atom.
- NM, atom is mainly empty space, PPM - negatively charged electrons embedded throughout so not empty space.
- PPM electrons and protons are distributed uniformly
NM electrons on edge and protons in middle.
What is the radius of the atom?
0.1nm or 1 x 10^-10m
What is the radius of the nucleus?
1 x 10^-14m (less than 1/10 000 of that of an atom)
Where is the mass of an atom concentrated?
In its nucleus.
What is meant by the relative mass of a particle?
The mass of one particle compared to another particle.
What is meant by the relative charge of a particle?
The charge of one particle compared to another particle.
Relative masses of protons neutrons and electrons:
P = 1
N = 1
E = very small
Relative charges of protons neutrons and electrons
P = +1
N = 0 (don’t have charge)
E = -1
Explain why atoms have no overall charge (2 marks)
- They have the same number of protons which are positive as electrons which are negative.
- So their charges cancel out
What is the bottom number on an atom?
The atomic number (represents the number of protons in an atom /and electrons of not an ion)