Chemistry Common Mistakes Paper 1

aqa paper 1 higher tier

behaviour of particles in a solid

* have a fixed shape and cannot flow, because their particles cannot move from place to place
* cannot be **compressed** (squashed), because their particles are close together and have no space to move into

behaviour of particles in a gas

* flow and completely fill their container, because their particles can move quickly in all directions
* can be compressed, because their particles are far apart and have space to move into

why can transition metals be used as a catalyst

they have a variety of different charged ions

anything using temp changes, what can you use as a control to improve accuracy

polystryene cup

what shape is Buckminster fullerene molecule

spherical

uses of fullerenes

* drug delivery - hollow
* hydrogen storage
* antioxidants
* catalysts (high sa to vol ratio)
* lubricants ( spherical so will roll)

why does sodium oxide have a high melting point

* giant structure
strong forces of attraction pulling them together
lots of energy needed to break them

what do you need to mention in practical questions

1. Control variables
2. Risk factors; solution
3. Independent variables
4. Method w/ instruments
5. Evaluative conclusion
6. Dependent variables

what's the difference between electrolysis and chemical cell

electrolysis uses electricity, chemical cell uses a chemical reaction

meaning of accuracy

1. the degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard

meaning of precision

refinement in a measurement, calculation, or specification, especially as represented by the number of digits given

how are soluble salts made

by reacting a dilute hydrochloric acid with an insoluble solid

give two limitations of this simple particle model for hydrogen gas

1. it doesn’t show movement
2. they r not 2d irl

1 mega joule = how many j

1,000,000

structure of a diamond

In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a very high melting point and does not conduct electricity

why does a diamond have a high MP

Diamond has a very high melting point because a large amount of energy is needed to overcome the many strong covalent bonds.

why does a diamond conduct no electricity

It does not conduct electricity as there are no delocalised electrons in the structure.

what is the structure of graphite

* In graphite, each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between the layers.
* In graphite, one electron from each carbon atom is delocalised.
* (graphite is similar to metals in that it has delocalised electrons.)

structure of graphene and how this makes it useful

Graphene is a single layer of graphite and has properties that make it useful in electronics and composites.

structure of carbon nanotubes

Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios. Their properties make them useful for nanotechnology, electronics and materials.

A different student produced a pure, dry sample of copper chloride using the same reaction.

How should the solution be heated gently in step 3; “Heat the solution gently until crystals start to form.”

using a (boiling) water bath or using an electric heater

state the law of conseration of mass

mass of products = mass of reactants

explain why the student should use a **pipette** to measure the dilute sulfuric acid and a **burette** to measure the sodium hydroxide volume

* pipette measures a fixed volume (accurately)
* burette measures variable volume

why is sodium chloride a strong electrolyte 

 The solution will have the maximum number of ions available to conduct electricity.

equation for a hydrogen fuel cell

2H2 + O2 ⟶ 2H2O

in refreence to bond energies, explain why something would be an exothermic reaction

* energy released forming (new) bonds is greater than energy needed to break (existing) bonds
* (so) energy is released (to the surroundings)

half equation for the reaction occurring at an electrode in 1 type of hydrogen fuel cell

H2 + 2OH− → 2H2O + 2 e−

why would a feul cell be described as an alkaline cell

contains OH− ions

how to find out how many protons there are

small #

how to find out how many neutrons there are

big number - small number

properties of the alkali metals (GROUP 1 METALS)

* are soft (they can be cut with a knife)
* have relatively low **melting points**
* have low densities

Give two differences between the properties of iron and sodium.

1. • iron has a higher MP/BP
2. • iron is dense(r)
3. • iron is hard(er)
4. • iron is strong(er)
5. • iron is less reactive
6. • iron has ions with different charges
7. • iron forms coloured compounds
8. • iron can be a catalyst

Chadwick’s experimental work on the atom led to a better understanding of isotopes.

Explain how his work led to this understanding.

1. Chadwick provided the evidence to show the existence of neutrons
2. (this was necessary because) isotopes have the same number of protons
3. but with different numbers of neutrons

what should you do when listing methods

independent, dependent, control,

when identifiying problems for 2&3 markers what should you do

1. identify the problem
2. give a solution

in graphite, each carbon forms _____ (covalent) bonds

3

The student made an error in selecting the apparatus for this investigation. How should the apparatus be changed?

1. use measuring cylinders, or gas syringes (instead of test tubes)
2. (Because) test tubes cannot measure the volume

Name the products formed when chlorine solution reacts with potassium iodide solution.

potassium chloride and iodine

Chlorine reacts with hydrogen to form hydrogen chloride.

Explain why hydrogen chloride is a gas at room temperature.

* hydrogen chloride is made of small molecules
* so has weak intermolecular forces
* that require little energy to overcome

Give one reason why it would be hazardous if water came into contact with sodium

* • very exothermic reaction
* • produces a corrosive solution
* • produces hydrogen, which is explosive / flammable

Explain why you would not expect titanium chloride to be a liquid at room temperature

* metal chlorides are usually ionic
* solid at room temperature / have high melting points
* due to them having strong (electrostatic) forces between the ions

why is graphite used for electrodes in electrolysis

its unreactive, can conduct electricity

what is a neutralisation reaction

A neutralisation reaction is a reaction between an acid and a base. Acids in solution are sources of hydrogen ions , H. + alkalis in solution are sources of hydroxide ions, OH.

write the ionic equation for the neutralisation reaction of hydrochloric acid with potassium hydroxide

H+ + 0H- → H2O

what is the ammonia from the Haber process used for

nitrogen based fertilisers

what does an ester bond look like

meaning of affinity

Affinity is the **tendency of a chemical species such as an atom or molecule to react with another to form a chemical compound**.

how did mendeleev organise the elements

arranging them in order of their atomic weight

what did mendie do with his version of the periodic table

* had gaps in it
* showed elements with similar chemical properties lined up in groups

properties of g7 metals

* simple **molecules**
* coloured vapours
* diatomic molecules
* form ionic salts w metals
* form molecular compounds with non metals
* \

characteristics of transition metals

* form coloured compounds
* catalytic properties
* ions w different charges

what’s the modern name for atomic weight

relative atomic mass

formula of molecule X in group 7

X2

Describe what you would see when sodium reacts with chlorine.

flame

white precipitate

Calcium hydroxide solution reacts with an acid to form calcium chloride. Complete the word equation for the reaction

hydrochloric (acid) water

Suggest one reason why it costs less to use nanoparticles rather than fine particles in suncreams

1. • less can be used (for the same effect)
2. • greater surface area (to volume ratio)

uses of nanoparticles

* catalyst
* electronics
* deoderant
* sun creamal

Give one limitation of using a dot and cross diagram to represent an ammonia molecule.

does not show the shape or only two-dimensiona

Hydrogen fuel cells can be used to power different forms of transport. Some diesel trains are being converted to run on hydrogen fuel cells.

**A newspaper article referred to the converted trains as the new ‘steam trains’. Suggest why.**

1. (in a fuel cell) hydrogen is oxidised (to produce water)
2. water is produced / released as gas / vapour / steam

Explain why a mixture is used as the electrolyte instead of using only aluminium oxide

1. mixture has a lower melting point (than aluminium oxide)
2. (so) less energy needed

Explain why sodium chloride solution cannot be used as the electrolyte to produce sodium metal.

1. hydrogen (gas) would be produced (instead of sodium)
2. (because) sodium is more reactive than hydrogen

Explain why the excess hydrogen must be burned off.

* to prevent hydrogen escaping (into the air)
* (because) hydrogen is explosive

John Dalton; Before the discovery of the electron, atoms were thought to be …..

tiny spheres that could not be divided.

John Dalton The discovery of the electron led to the ….

plum pudding model of the atom.

The results from the alpha particle scattering experiment led to….

nuclear model replaced the plum pudding model

how did the alpha particle scattering experiment change the model

Most alpha particles went straight through the foil. But a few were scattered in different directions.

* the mass of an atom is concentrated at its centre, the **nucleus**
* the nucleus is positively charged

Niels Bohr adapted the nuclear model by suggesting that ….

electrons orbit the nucleus at specific distances. The theoretical calculations of Bohr agreed with experimental observations.

physical properties of group 1 elements

* soft
* low mp
* malleable
* not useful as cataylyst

physical properties of transition metals

* they are good conductors of heat and electricity.
* high mp
* dense
* strong

what kind of cup should you use for investigations that measure temp

polystyrene

what do labels x and y rep

(X) energy (Y) (overall) energy change

why is it suitable for drug delivery

* hollow
* unreactive
* non toxic
* high sa to vol ratio
* \

why is the solid in excess rather than the liquid

excess) zinc oxide can be filtered off

the noble gases have boiling points that increase going down the trt/f

true

Give one reason why the products are difficult to separate if magnesium is used to reduce silicon dioxide.

both products are solid

what does higher strength of an acid mean

• the stronger an acid the greater the ionisation / dissociation (in aqueous solution) • (so) the stronger the acid the lower the pH

what does higher conc of an acid mean

* • the higher the concentration of an acid the more acid / solute in the same volume (of solution)
* • (so) the higher the concentration of the acid the lower the pH

why is there no electrical conductivity in barium sulphate

* there are no ions that are free to move (
* because) barium sulfate is solid / insoluble
* (and) hydrogen ions have reacted with hydroxide ions to produce water

which are in the same period

m &q

electrolysis materials

behaviour of particles in a liquid

* flow and take the shape of their container, because their particles can move around each other
* cannot be compressed, because their particles are close together and have no space to move into

how can the atom economy of a reaction be improved

find a use for the waste

change reaction to reduce waste

why does iodine have a higher bp than chloring

the FORCES between iodine molecules are stronger

why does potassium iodide conduct electricity

it contains IONS which are free to move

why is X positioned in group Y of the periodic tablle

it has Y outer electrons

how can ionic compound conduct electricity when molten

IONS are free to move

saftey precautions when heating contents in an evaporating dish

wear googles

what is the half equation for what happens at the negative electrode in fuel cells (anode)

**2H2 → 4H+ + 4e–**

what is the half equation for what happens at the positive electrode in fuel cells (cathode)

4H+ + O2 + 4e– → 2H2O

what is the total equation for what happens in hydrogen fuel cells

2H2 + O2→ 2H2O

what is meant by a strong acid

fully ionised when disolved in water

to form h+ ions

how does a covalent bond hold atoms together

the positive nuclei from two different atoms are held together by their common attraction for the shared pair of electrons held between them.

how does an ionic bond hold atoms together

strong electrostatic forces of attraction between the oppositely charged ions. The forces act in all directions in the lattice. This is called ionic bonding .