past paper questions chemistry

give one use of aluminium oxide

sandpaper/gemstones/ in toothpaste/ in comestics

explain in terms of intermolecular forces, why ice cubes float in the water

• water forms four hydrogen bonds

• in ice the hydrogen bonds hold water molecules in a lattice with gaps between the molecules whereas in water the molecules move around each other with no gaps

• the density of ice is less than the density of water

esuflur is an element in period 3

sulfur reacts with oxygen to form sulfur dioxide

explain why sulfur dioxide does not conduct electricity

• covalent compound

• no free electrons or ions to carry a current

• no charged particles to carry a current

explain what is meant by the term limiting reactant

the reactant that is used up first, stopping the reaction from producing any more product

explain what effect a limiting reactant has on a reaction

determines the maximum amount of product that can be formed because it is used up first, causing the reaction to stop even if other reactants remain

explain why water is a polar molecule

• oxygen is more electronegative than hydrogen

• so oxygen pulls electrons towards it

• making H slightly positive and O slightly negative

• the molecule is not linear and so the charges do not balance

state one use of carbon dioxide

• fire extinguisher

• dry ice

• coolant

• fizzy drinks

Aluminium, Al, can from aluminium ions, Al3+.

Describe how aluminium atoms form aluminium ions

• electrons are lost from outer shell

• three electrons

Describe the structure of an ionic compound

• there is an lectrostatic attraction between the ions

• contains positive and negative/ oppositively charged ions

• arranged in a giant ionic lattice/ giant ionic structure

state two physical properties of simple covalent molecules

• low melting point

• poor conductors of electricity

Aluminium is a metal

Aluminium is used in power lines

One reason why aluminium can be used in power lines is because it is ductile

State one other physical property that makes aluminium suitable for use in power lines

• lightweight

• electrical conductivity

• low denisty

• high melting point

• malleable

• conducts a current

• resistant to corrosion/ does not corrode

explain why metals are ductile

you should refer to atoms in your answer

• atoms are arranged in regular layers/ atoms are all the same size

• atoms can move over one another easily

copper metals have many uses

for example, copper can be used to make wires because copper metal is ductile

state one other use of copper and the property that it mst have for this use

• layers of cations held together by delocalised eletrons/metallic bonding

• cations can move over one another when force is applied

• so the copper can be stretched

describe how copper conducts an electrical current

• delocalised electrons

• electrons move

describe what is meant by a dative covalent bond?

• shared pair of electrons

• both electrons come from one element

give one property of a transition metal

• can have different oxidation states

• hard

• ductile

• shiny

• high melting point

hydrogen -253

oxygen -183

explain why the boiling poit of hydrgen is lower than the boiling point of oxygen

• hydrogen has fewer electrons than oxygen

• weaker van der waals forces

• therefore less energy/ heat to break van der waals forces

give 1 physical property of group 1 metals

• soft

• conducts electricity

• malleable

• low density

• conducts heat

• ductile

explain why copper is ductile

• atoms are in rows/layers

• that slip/move over each other

• so metal can be drawn into wires without breaking

Na,Mg,Al,Si,P,S,Cl,Ar

Explain the trend in melting point from sodium to aluminium

• melting point increases from Na to Al

• more electrons lost from outer shell

• ions are more positively charged

• same amount of shielding

• stronger electrostatic attraction between positive ions

• larger amount of energy to break the electrostatic attraction

the electronegativity of the halogens changes down group 7

explain how electronegativity chnages down group 7

• H^+ doe not have any electrons/ is electron deficient

• shared pair of electrons

• lone pair of electrons come from the nitrogen