Topic 5 - Separate Chemistry I

properties of transition metals(7)

very lustrous

hard

strong

good heat conductors

good electrical conductors

highly dense

very high mps

oxidation state

a number given to show if the element has been oxidised or reduced. The oxidation state of an ion is simply the charge on the ion

Do transition metals have just one oxidation state?

No they can have more than one

Why can transition metals have more than one oxidation state?

They can lose a different number of electrons depending on the chemical environment they are in

Are transition metals colourful?

No but the compounds they form are

How does the differing oxidation state of a transition metal have on its compounds in aqueous solutions?

They will have differing properties and colours

Uses of transition metals(3)

catalysis

medicine

other industrial applications

Why are transition metals used in catalysis?

They can be used as catalysts as their catalytic characteristics stem from their ability to interchange between a range of oxidation states.

This allows them t form complexes with reagents that can easily donate and accept electrons from other chemical species within a reaction system

What is iron used in?

The Haber Process

What is nickel used in?

the hydrogenation of alkenes

What is vanadium pentoxide used in?

The Contact Process to produce sulfuric acid

Why are transition metals used in medicine

Due to their hardness and strength, they can be used in surgical applications such as limb and joint replacement.

Titanium is useful in particular as it is the only element that can bond with bones due to its high biocompatibility

How are transition metals used in industrial applications?

They can form coloured compounds for dyes and paints

They are used in creating stained glass, jewellery and in anti-corrosive materials

corrosion

the destruction of materials by chemical substances in their environment which act on them over a period of time

Most metals corrode in which gas presence to form what compound?

oxygen to form a metal oxide

What type of reaction is corrosion caused by and how?

Redox

Tis is because the metal loses electrons and is oxidised whilst the oxygen gains electrons and is reduced

rusting

the corrosion of specifically iron in the presence of water and oxygen in the air

rusting equation

iron + water + oxygen ⟶ hydrated iron(III)oxide

How do barrier methods prevent rusting?

They prevent the iron from coming into contact with water and oxygen

Problems with barrier methods?

If the coating is washed away are scratched the iron is again exposed to water and oxygen and will rust

Common barrier methods(4)

grease

oil

paint

plastic

What metal is used in galvanising?

Zinc

Why does galvanising work?

Because zinc is more reactive than iron

How does galvanising work?

Iron is coated in a layer of zinc.

A barrier method is formed when zinc reacts with oxygen and carbon dioxide in the air to form zinc carbonate

If the coating is damaged/scratched then zinc anyways preferentially corrodes due to its higher reactivity position and loses its 2 electrons and the iron stays protected as it accepts the electrons released by zinc, remaining in the reduced state and thus it doesn’t undergo oxidation

The electrons donated by zinc also reacts with hydrogen ions in the water producing hydrogen gas

Therefore zinc reacts with oxygen and water and corrodes instead of the ion

sacrificial corrosion

when a more reactive metal is intentionally allowed to corrode

Where is sacrificial corrosion used?

In ships’ hulls which sometimes have large blocks of magnesium or magnesium alloys attached which corrode de and provide protect to the hull the same way zinc does by pushing electrons onto the iron which prevents it from being oxidised

electroplating

a process where the surface of one metal is coated with a layer of a different, less reactive metal

What is the anode in electroplating?

The pure substance used to coat

What is the cathode in electroplating?

The object to be electroplated

What is the electrolyte in electroplating?

An aqueous solution of a soluble salt of the pure metal at the anode

Uses of electroplating(3)

Makes metals more resistant to corrosion or damage

For a tin can(actually a steel can with 1% tin on the interior surface) it can resist corrosion from the liquids inside

Improving the appearance of metals e.g. silver plating cutlery and jewellery

alloys

mixtures metals where the metals are mixed together physically but not chemically combined

What properties do alloys have to can be different to the metals the contain?

Greater strength

greater hardness

greater resistance to corrosion

extreme temperatures

Why are alloys much harder than pure metals?

They contain atoms of different sizes which distorts the regular lattice arrangements of atoms

This makes it more difficult for the layers to slide over each other so they are usually much harder than the pure metal

What is cast iron?

Iron from a blast furnace.

It is an alloy of 96% iron with carbon phosphorus, silicon, and sulfur impurities

Why is cast iron converted into steel?

It is too brittle for many used

What is iron alloyed with in mild steel?

0.25% carbon

What is iron alloyed with in high carbon steel?

0.5-1.4% carbon

What is iron alloyed with in low alloy steel?

1-5% of other metals(chromium, nickel, titanium)

What is iron alloyed with in stainless steel?

20% chromium

10% nickel

Uses of mild steel

car body panels

wires

uses of high carbon steel

tools and chisels

Uses of low alloy steel

construction bridges

high speed tools

Uses of stainless steel

cutlery and sinks

chemical plants

properties of mild steel

relatively soft

tough

malleable

magnetic

cheap

can be recycled

properties of high carbon steel

hard but brittle

properties of low alloy steel

hard and strong

low ductility

low malleability

properties of stainless steel

strong

resistant to corrosion

Are alloys a compound?

no

What is magnalium

an aluminium alloy

What are the properties of magnalium(5% Mg)?

Lighter

stronger

more corrosion resistant than aluminium

What is magnalium(5% Mg) used in?

Automobile and aircraft construction

What is magnalium (50% Mg) used in and why?

The production of fireworks as it is more stable than pure magnesium but still burns brightly

Uses of aluminium(5)

aeroplane bodies

overhead power cables

saucepans

food cans

window frames

Why is aluminium used in aeroplane bodies?

High strength to weight ratio(low density)

Why is aluminium used in overhead power cables?

good conductor of electricity

Why is aluminium used in saucepans?

good heat conductor

Why is aluminium used in food cans?

non toxic

corrosion resistant

acidic food stuffs

Why is aluminium used in window frames?

Corrosion resistant

bronze

an alloy made of copper and tin

Is bronze harder than copper or the other way around?

bronze > copper

uses of bronze

making ornaments and medals

brass

an alloy containing 70% copper and 30% zinc

properties of brass

decorative

corrosion resistant

uses of brass

low friction ornamental purposes such as plumbing and carpentry fittings

uses of copper

electrical wires

water pipes

Why is copper used in electrical wires?

It’s a good electrical conductor and malleable

Why is copper used in water pipes?

Easy to work with and bend

non-toxic

unreactive(doesn’t react with water)

properties of gold

soft

malleable

What do carats represent?

The purity of gold jewellery

What is the maximum carat?

24 carat

(100% gold)

What does a 12 carat piece of jewellery at 50g contain?

50% gold

therefore 25g of the jewellery is pure gold

concentration formula in mol/dm3

number of moles of solute(mol) / volume of solution(dm3)

How do go from g/dm3 to mol/dm3 and vice versa

g/dm3 to mol/dm3 - divide by molar mass in grams

mol/dm3 to g/dm3 - multiply by molar mass in grams

How to go from cm3 to dm3 and vice versa

cm3 to dm3 - divide by 1000

dm3 to cm3 - multiply by 1000

Equipment for preparing the solution to add for a titration

The solution plus indicator is added into the burette

CP: Titration Steps

1. Use the pipette and pipette filler and place exactly 25 cm³ sodium hydroxide solution into the conical flask

2. Place the conical flask on a white tile so the tip of the burette is inside the flask

3. Add a few drops of a suitable indicator to the solution in the conical flask

4. Perform a rough titration by taking the burette reading and running in the solution in 1 – 3 cm³ portions, while swirling the flask vigorously

5. Quickly close the tap when the end-point is reached (sharp colour change) and record the volume, placing your eye level with the meniscus

6. Now repeat the titration with a fresh batch of sodium hydroxide

7. As the rough end-point volume is approached, add the solution from the burette one drop at a time until the indicator just changes colour

8. Record the volume to the nearest 0.05 cm³

9. Repeat until you achieve two concordant results (two results that are within 0.1 cm³ of each other) to increase accuracy

How to complete titration calculations?

Step 1: Write out the balanced equation for the reaction

Step 2: Calculate the moles of the known solution given the volume and concentration

Step 3: Use the equation to deduce the moles of the unknown solution

Step 4: Use the moles and volume of the unknown solution to calculate the concentration

yield

the amount of product you get from a reactant

Is 100% yield possible in reality?

No, never

Why is yield never 100% in reality?

Some reactants may be left behind in the equipment

Reversible reactions will never get high yield as products are turning back into reactants

Products may be lost during separation and purification stages such as filtration or distillation

There may be side reactions where a substance reacts with a gas in the air or an impurity in 1 of the reactants

Products can also be lost from transfer of one container to the other

actual yield

the recorded amount of product obtained

theoretical yield

the amount of product that would be obtained under perfect practical and chemical conditions

How is theoretical yield calculated?

From the balanced equation and the reacting masses

percentage yield equation

actual yield/theoretical yield x 100

reaction pathways

a sequence of reactions which must occur to produce the required product.

Does a compound have only 1 reaction pathway?

No, multiple reaction pathways can lead to the creation of the same compound

Why is percentage yield useful in industry?

It allows companies to test out different reaction pathways and these are then compared and evaluated so that a manufacturing process can be chosen

atom economy

a way of measuring the efficiency of a reaction by comparing the amount of useful products measured to the total amount of products made

Why is atom economy important for industry?

Used in an effort to obtain sustainable development

The higher the atom economy the more sustainable that process is

It is also economically better to use processes with higher atom economies

atom economy formula

total relative formula mass of desired product/total relative formula mass of all products x 100

What must you remember about the RFM when doing atom economy?

Include the superscript(the coefficient)

What is the problem with low atom economy reactions?

They use up a lot of resources and produce a lot of waste material that need to be exposed of.

It’s pretty expensive as raw materials and the waste disposal(which requires chemicals equipment, space and transport)

How can atom economy be improved?

Finding a way to make the waste products useful

Selling or reusing the waste products could help

Considering alternative methods of production that may produce a more useful by product is also not a bad idea

molar volume equation

amount of gas moles x 24(dm3/mol)

Avogadro’s Law

Equal volumes of all gases at the same temperature and pressure, contain the same number of molecules and moles

What are the conditions for room temperature?

20 degrees Celsius

1 atm

1 mole of any gas at room temperature occupies what volume?

24 dm3/mol

What does the stoichiometry of a reaction and Avogadro’s Law enable us to do?

deduce the exact volumes of gaseous reactants and products

If gas volumes are not in the same ratio as the coefficients then what determines the amount of product?

The amount of product is determined by the limiting reactant so it is essential to identify it first