GCSE Chemistry 4 & 6 markers

Describe how the process of distillation using a condenser produces pure water from salt solution

[4 marks]

- solution is heated

- water evaporates

- the vapour cools in the condenser

- the vapour condenses

or

- the vapour turns to liquid

- (pure) water collected in a beaker

Evidence from the alpha particle scattering experiment led to a change in the model of the atom from the plum pudding model

Explain how

[4 marks]

- most (alpha) particles passed straight through (the gold foil)

- (so) the mass of the atom is concentrated in the nucleus / centre

or

- (so) most of the atom is empty space

- some (alpha) particles were deflected / reflected

- (so) the atom has a (positively) charged nucleus / centre

Compare the plum pudding model with the nuclear model of the atom

[4 marks]

Plum pudding model

- ball of positive charge (spread throughout)

- electrons spread throughout (embedded in the ball of positive charge)

- no empty space in the atom

- mass spread throughout

Nuclear model

- positive charge concentrated at the centre

- electrons outside the nucleus

- most of the atom is empty space

- mass concentrated at the centre

Compare the chemical and physical properties of transition elements and Group 1 elements

[6 marks]

Physical

Transition elements

- high melting points

- high densities

- strong

- hard

Group 1

- low melting points

- low densities

- soft

Chemical

Transition elements

- low reactivity / react slowly (with water or oxygen)

- used as catalysts

- ions with different charges

- coloured compounds

Group 1

- very reactive / react (quickly) with water / non-metals

- not used as catalysts

- white / colourless compounds

- only forms a +1 ion

Describe what happens when sodium reacts with fluorine to produce sodium fluoride

[4 marks]

- sodium (atom) loses

- fluorine (atom) gains

- one electron

- ions formed

Explain why the reactivity of elements changes going down Group 1

[4 marks]

- reactivity increases (going down the group)

- (because) the outer electron / shell is further from the nucleus

- (so) there is less attraction between the nucleus and the outer electron / shell

- (so) the atom loses an electron more easily

Explain the trend in boiling points of the halogens

[4 marks]

- (boiling point) increases (down the group)

- (because) the relative formula / molecular mass increases

or

- (because) the size of the molecule increases

- (so) the intermolecular forces increase (in strength)

- (so) more energy is needed to overcome the intermolecular forces

Explain why the reactivity of the elements increases going down Group 1 from lithium to rubidium but decreases going down Group 7 from fluorine to iodine

[4 marks]

- relative distance from nucleus

- relative attraction to nucleus

- relative ease of gain of loss of electron

- opposite explanation of ease of gain or loss of electron for other group

Evaluate Newlands' and Mendeleev's tables

You should incude:

- a comparison of the tables

- reasons why Mendeleev's was more acceptable

Comparative points

- both tables have more than one element in a box

- both have similar elements in the same column

- both are missing the noble gases

- both arranged elements in order of atomic weight

Advantages of Mendeleev / disadvantages of Newlands

- Newlands did not leave gaps for undiscovered elements

- Newlands had many more dissimilar elements in a columnn

- Mendeleev left gaps for undiscovered elements

- Mendeleev changed the order of some elements (e.g. Te and I)

Points which led to the acceptance of Mendeleev's table

- Mendeleev predicted properties of missing elements

- elements with properties predicted by Mendeleev were discovered

- Mendeleev's predictions turned out to be correct

- elements were discovered which fitted the gaps

Plan an investigation to identify magnesium, iron and copper by comparing their reactions with dilute hydrochloric acid

[4 marks]

Key steps

- add the metals to (dilute) hydrochloric acid

- measure temperature change

or

- compare rate of bubbling

or

- compare colour of resulting solution

For copper

- no reaction

- shown by no temperature change

or

- shown by no bubbles

For magnesium and iron

- magnesium increases in temperature more than iron

or

- magnesium bubbles faster than iron

or

- magnesium forms a colourless solution and iron forms a coloured solution

Control variables

- same concentration / volume of hydrochloric acid

- same mass / moles of metal

- same particle size of metal

- same temperature (of acid if comparing rate of bubbling)

Titanium chloride is a liquid at room temperature

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

[3 marks]

- metal chlorides are usually ionic

- (so)(metal chlorides) are solid at room temperature

or

- (so)(metal chlorides) have high melting points

- (because) they have strong (electrostatic) forces between the ions

or

- (but) must be a small molecule or covalent

Explain why graphite is:

- a food electrical conductor

- soft and slippery

You should answer in terms of structure and bonding

[6 marks]

- bonds are covalent

- giant / molecular structure

- three (covalent) bonds per carbon atom

or

- only three electrons per carbon atom using in (covalent) bonds

- so one electron per carbon atom (is delocalised)

- can move through the structure

- carrying (electrical) charge

- so graphite conducts electricity

- layered structure

- of (interlocking) hexagonal rings

- with weak (intermolecular) forces between layers

or

- no (covalent) bonds between layers

- so the layers can slide over each other

- so graphite is soft and slippery

Compare the structure and bonding of the compounds:

- carbon dioxide

- magnesium oxide

- silicon dioxide

[6 marks]

- (both) carbon dioxide and silicon dioxide are made up of atoms

- (but) magnesium oxide is made up of ions

- (both) silicon dioxide and magnesium oxide are giant structures

- (but) carbon dioxide is small molecules

- with weak intermolecular forces

- all three compounds have strong bonds

- (both) carbon dioxide and silicon dioxide are formed from two non-metals

- (so) bonds are covalent

- (so) electron (pairs) are shared (between atoms)

- (but) magnesium oxide is formed from a metal and a non-metal

- (so) bonds in magnesium oxide are ionic

- (so) electrons are transferred

- from magnesium to oxygen

- two electrons are transferred

- bonds in silicon dioxide are single bonds

- (where) each silicon forms four bonds

- (and) each oxygen forms two bonds

- (but) in carbon dioxide the bonds are double bonds

- (where) carbon forms two double bonds

- (and) oxygen forms one double bond

Describe what happens when a lithium atom reacts with a chlorine atom

Answer in terms of electrons

[4 marks]

- lithium (atom) loses (one) electron(s)

- chlorine (atom) gains (one) electron(s)

- reference to transfer of one electron

- to form positive and negative ions

Explain why nitrogen is a gas a room temperature

Answer in terms of nitrogen's structure

[3 marks]

- weak forces

- between molecules

or

- intermolecular

- (which) need little energy to overcome

Describe what happens when two atoms of potassium react with one atom of sulfur

Give your answer in terms of electron transfer

Give the formulae of the ions formed

[5 marks}

- electrons transferred from potassium to sulfur

- two potassium atoms each lose one electron

- forming K+ / 1+ ions

- sulfur atoms gain 2 electrons

- forming s2- / 2- ions

Describe an investigation to compare the reactivity of an unknown metal with that of zinc

[4 marks]

- measure temperature change

- when each metal is added to silver nitrate solution

- same concentration / volume of solution

or

- same mass / moles of metal

- the greater the temperature change the more reactive

Graphite is a form of carbon

Graphite is soft and is a good conductor of electricity

Explain why graphite has these properties

Answer in terms of binding a structure

[4 marks]

- each (carbon) atom forms three covalent bonds

- forming layers (of hexagonal rings)

(soft)

- (because) layers can slide over each other

(conducts electricity)

- (because of) delocalised electrons

Copper, iron, magnesium and zinc are placed in order of their reactivity

Describe a method to find the position of an unknown metal in this reactivity series

[4 marks]

- suitable method described

- the observations / measurements required to place in order

- an indication of how results would be used to place the unknown metal in the reactivity series

- a control variable to give a valid result

Describe how a titration could be completed using the following equipment:

- measuring cylinder

- potassium hydroxide solution

- conical flask

- indicator

- sulfuric acid

- burette

[5 marks]

- add potassium hydroxide (solution) to the (conical flask)

- add (a few drops of) indicator

- add the (sulfuric) acid (from the burette)

- until the colour (of the indicator) changes

- read the volume from the burette

Two samples of dilute sulfuric acid are tested, P and Q

Describe how to use titrations to find which sample, P or Q, is more concentrated

[6 marks]

Key steps

- measure the volume of acid

- add indicator to the acid

- add sodium hydroxide solution

- until the colour changes

- record volume of sodium hydroxide solution added

- repeat procedure with the other acid

Use of results

- compare the two volumes of sodium hydroxide solution to find which sample P or Q is more concentrated

Other points

- pipette to measure volume of acid

- use a few drops of indicator

- swirl

- use a white tile

- rough titration to find approximate end point

- add dropwise near the endpoint

- read volume from bottom of meniscus

- repeat and take a mean

Describe a method to make pure, dry crystals of magnesium sulfate from a metal oxide and a dilute acid

[6 marks]

- use magnesium oxide and sulfuric acid

- add sulfuric acid to a beaker

- warm sulfuric acid

- add magnesium oxide

- stir

- continue adding until magnesium oxide is in excess

- filter

- using a filter paper and funnel

- to remove excess magnesium oxide

- heat solution in an evaporating basin

- to crystallisation point

- leave to crystallise

- pat dry with filter paper

Describe a method to find the exact volume of sodium hydroxide that reacts with 25.0 cm3 of hydrochloric acid

[6 marks]

- fill burette with sodium hydroxide

- add sodium hydroxide from the burette to the hydroxide and indicator

- stop when colour changes

- measure volume used from burette

Plus any two from

- stand flask on white tile

- swirl

- add dropwise near endpoint

- repeat

Describe a safe method for making pure crystals of copper sulfate from copper carbonate and dilute sulfuric acid

In your method you should name all of the apparatus you will use

[6 marks]

- sulfuric acid in beaker (or similar)

- add copper carbonate one spatula at a time

- until copper carbonate is in excess or until no more effervescence occurs

- filter using filter paper and funnel

- filter excess copper carbonate

- pour solution into evaporating basin / dish

- heat using Bunsen burner

- leave to crystallise / leave for water to evaporate / boil off water

- decant solution

- pat dry (using filter paper)

- wear safety spectacles / goggles

Describe how a sample copper chloride crystals could be made from copper carbonate and dilute hydrochloric acid

[4 marks]

- add excess copper carbonate (to dilute hydrochloric acid)

- filter (to remove excess copper carbonate)

- heat filtrate to evaporate some water or heat to point of crystallisation

- leave to cool (so crystals form)

25.0cm3 of sodium hydroxide of unknown concentration was added to a conical flask

A titration was carried out to find what volume of 0.100 mol/dm3 sulfuric acid is needed to neutralise the sodium hydroxide

Describe how the titration would be completed

You should name a suitable indicator and give the colour change that would be seen

[4 marks]

- add indicator, e.g. phenolpthalein / methyl orange / litmus added to sodium hydroxide (in the conical flask)

- (adds the acid from a) burette

- with swirling or dropwise towards the end point or until the indicator just changes colour

- until the indicator changes from pink to colourless (for phenolpthalein) or yellow to red (for methyl orange) or blue to red (for litmus)

Explain, in terms of particles, how and why the rate of reaction changes due to the reaction of calcium carbonate with hydrochloric acid

[4 marks]

- acid particles used up

- so concentration decreases

- so less frequent collisions

- so rate decreases / reaction slows down

A tritration is used to check if two samples of hydrochloric acid, A and B, are the same concentration

Describe how this would be carried out

[6 marks]

- acid in burette or flask

- alkali/sodium hydroxide or acid in burette or flask

- volume of acid or alkali measured using pipette

- indicator in flask

- white tile under the flask

- slow addition

- swirling / mixing

- colour change of indicator

- burette volume measured

Electrolysis is carried out using copper nitrate solution

Some of the copper produced did not stick to the negative electrode and fell to the bottom of the beaker

Suggest how the total mass of copper produced could be found

[4 marks]

- filter the mixture

- wash and dry the copper / residue

- weigh the copper collected

- add to the increase in mass of the electrode

Describe in terms of electrons, what happens when a magnesium atom reacts with chlorine atoms to produce magnesium chloride

[4 marks]

- magnesium loses two electrons and chlorine gains one electron

- one magnesium and two chlorines

- noble gas structure or eight electrons in the outer shell or (electrostatic) attraction between ions or forms ionic bonds