OCR Gateway Chemistry: C4

What is another name for Group 1?

Alkali metals

What is the electronic structure of Group 1 metals?

1 electron in outer shell so forms +1 ion

Describe reactivity in group 1

Reactivity increases down the group.

This is because the atoms are larger further down the group and it is easier for the outer electron to be lost. The atom is oxidised more easily

What are some physical features of Group 1 metals? (3)

They are solids but soft and easy to cut

They are shiny but tarnish quickly

They have typical metal properties (conduct electricity, malleable etc.)

Describe the reactions of Group 1 metals

They react rapidly with air and water so are stored under oil

React with water to form an alkali and all follow the same pattern

2Na(s) +2H20(l) -> 2NaOH(aq) + H2(g)

Describe the melting point of Group 1 metals

Melting point decreases down the group

What are features of Group 0 gases? (Melting point, reactivity, state of matter)

-Non-metal gases

-Weak forces of attraction between atoms so they have low melting and boiling points

-Melting point increases down the group as atoms get larger so there is a stronger attraction between the atoms

-Inert (unreactive)

What is another name of Group 0

Noble gases

Describe atomic structure of Group 0 gases

-Exist as monatomic single atoms

-8 electrons on outer shell so very unreactive

What is an alternative name for Group 7 atoms?

Halogens

What are features of Group 7 atoms? (properties, melting point, reactions)

Typical non- metal properties (don't conduct electricity, brittle when solid)

Melting point increases down group as molecules get larger so they have stronger intermolecular forces

They react vigorously with Group 1 metals to produce salts

Describe reactivity of Group 7

Reactivity decreases down group.

This is because atoms are larger further down the group and it is harder for them to gain an outer electron. The atom is reduced less easily.

Cl2 +2e- -> 2Cl-

Describe atomic structure and forces of group 7

- 7 electrons in outer shell so form -1 ion

- Exist as diatomic molecules

- Strong covalent bond within the molecule but weak intermolecular forces between molecules so low melting/boiling point

What is the colour and state of fluorine?

Pale yellow, Gas

What is the colour and state of chlorine?

Pale green, gas

What is the colour and state of bromine?

Orange-brown, liquid

What is the colour and state of iodine?

Grey, solid

What is a halide?

A compound containing a halogen as an ion e.g. NaCl,HBr

How do halogen displacement reactions work?

A more reactive halogen can displace a less reactive hallogen from it's solution if it is a halide

Show an example of bromine being displaced by chlorine

Cl2 (aq) +2NaBr (aq) -> 2NaCl (aq) + Br2 (aq)

Show a half equation for the displacement reaction between chlorine and bromine

Reduction: Cl2 (aq) + 2e- -> 2Cl-

Oxidation: 2Br- -> Br2 +2e-

Show an ionic equation for the displacement reaction between chlorine and bromine

Cl2(aq) + 2Br- -> 2Cl- + Br2

What can you see in a halogen displacement reaction?

What are the features of transition metals

-Typical metal properties (conduct electricity, strong, malleable etc) but harder, more dense and with higher melting points than Group 1

- Good catalysts

- Platinum, palladium and rhodium are used in catalytic converters in cars to turn harmful vehicle fumes into less harmful ones

Describe reaction of transition metals

- Produce coloured compounds when they react

- Iron reacts with water and oxygen to form rust

- 4Fe(s) + 3O2(g) --> 2Fe2O3 (s)

- Form more than one type of ion e.g. Fe(II) and Fe(III)

What does the rate at which a reaction takes place show?

relative reactivity of a substance

When can metals react with acid or water and why?

If they are more reactive than hydrogen they can react with acid or water as they are able to displace it out of the acid or water

What is the reactivity series?

How can you tell if one metal displaces another

Colour change

If the metal is not more reactive then there is no colour change

Describe what you can see when copper displaces silver

Copper is more reactive than silver so it can displace it.

You would see the solution turn blue as blue copper nitrate solution is produced and a silver coating appear on the surface of copper peices.

What are trends in reactivity?

Reactivity increases down the metal groups

Reactivity decreases down the non-metal groups

Francium and Fluorine are most reactive

How can you test for oxygen?

It will relight a glowing splint

How can you test for hydrogen?

Squeaky pop test with a lit splint

How can you test for carbon dioxide?

Bubble it through limewater, Ca(OH)2- it will go cloudy

If you carry on bubbling CO2 through the limewater the CaCO3 dissolves so the cloudy appearance disappears.

Describe testing for limewater in terms of an equation

The water in limewater reacts with CO2 to make carbonic acid H2CO3:

H2O(l) + CO2(g) --> H2CO3(aq)

H2CO3 (aq) + CaCo --> Ca(HCO3) (aq)

How do you test for chlorine?

Bleaches damp blue litmus paper

OR

Damp starch-iodide paper turns blue/black

How do you test for cations?

Flame test

OR

Hydroxide precipitate test

What happens in a flame test?

1. Dip nichrome wire in conc HCl to clean it

2. Dip into substance to be tested

3. Hold it in a blue flame

What colour does calcium go in a flame test?

orange/red

What colour does copper go in a flame test?

green/blue

What colour does potassium go in a flame test?

lilac

What colour does lithium go in a flame test?

red

What colour does sodium go in a flame test?

yellow

How does a hydroxide precipitate test work?

1. Add a few drops of NaOH and you will see a coloured precipitate as a hydroxide forms

2. If you see a white precipitate, add more NaOh and see if the precipitate dissolves

Why does a hydroxide precipitate test not work with group 1 ions?

They form a hydroxide that dissolves so there is no precipitate

What colour precipitate does Fe(II) have?

green

What colour precipitate does Fe(III) have?

orange/brown

What colour precipitate does Cu(II) have?

blue

What colour precipitate does Ca(II) have?

White

Need to add excess NaOH, it does not dissolve with excess NaOH so stays white

What colour precipitate does Mg(II) have?

White

Need to add excess NaOH, it does not dissolve with excess NaOH so stays white

What colour precipitate does Zn(II) have?

White

Need to add excess NaOH, it does dissolve with excess NaOH so does not stay white

What colour precipitate does Al(III) have?

White

Need to add excess NaOH, it does dissolve with excess NaOH so does not stay white

How do you test of sulphate ions? (SO4 2- (aq) )

1. Add a few drops of HCl (aq) and then a few drops of BaCl2 (aq)

2. If sulphate ions are present then a white precipitate of BaSO4 (s) will appear, this is insoluble in HCl

Ionic equation:

Ba 2+ + SO4 2- -->BaSO4 (s)

How do you test of carbonate ions? (CO3 2- (aq) )

1. Add a few drops of HCl (aq)

2. If CO3 2- ions are present then you will see effervesence as CO2 is produced.

3. This can be confirmed by using limewater

What is the ionic equation for testing for carbonate atoms?

2H+ (aq) + CO3 2- --> CO2(g) + H2O (l)

How do you test for Cl-, Br- and I- ions?

1. Add a few drops of HNO3 (aq) to make sure no carbonate ions are present

2. Add a few drops of AgNO3 (aq)

3. If a halide ion is present you will see a precipitate

Cl- :is a white precipitate

Br- :is a cream precipitate

I- :is a yellow precipitate

What is instrumental analysis?

Where a machine carries out analysis of a sample rather than a person

What's the advantages of instrumental analysis?

More accurate

Faster

More sensitive ( means they can analyse very small amounts of a sample e.g. from a crime scene)

What can a gas chromatograph tell you?

-The number of compounds in a mixture = the number of peaks

-How much of each compound is in the mixture = area under graph

- Retention time = time taken for a substance to travel through the chromatography column and is different for different substances

What can a mass spectrometer tell you?

-Mass of atoms or molecules

- Amount of isotopes for an element

- Structure of molecules

How does a mass spectrometer work?

1. Sample is ionised to form a molecular ion

2. This breaks up into fragments of molecules which are then detected

3. Far right peak is the molecular ion peak and the value = Mr

What can infrared spectroscopy tell you?

Covalent bonds in a sample by looking at the graph and looking up values in the table

(they have a graph and table)