Topic 5- Separate chem I

Question 1

What is corrosion ?

Answer 1

• when a metal oxidises – usually given to iron or steel

- example of redox reaction

Question 2

How to prevent rusting?

Answer 2

• painting -same as oil or grease
• oil or grease - forms protective coat around metal
• coating w/ plastic

Question 3

How does galvanising iron protect it from corrosion

Answer 3

• zinc more reactive than iron so reacts instead of iron

Question 4

How does sacrificial protection protect iron from corrosion

Answer 4

• more reactive metal connected to iron, so corrodes instead

Question 5

How does tin plating iron protect it from corrosion

Answer 5

• tin coat protects iron underneath
• less reactive, so acts as barrier – if tin scratched iron will rust
• quite cheap

Question 6

How does alloying iron protect it from corrosion

Answer 6

• other elements increase corrosion resistance

Question 7

Percentage yield equation

Answer 7

percentage yield = yield obtained/ predicted yield x 100 (for percentage)

Question 8

What is the yield of a reaction?

Answer 8

• amount of chemicals produced during during a reaction

Question 9

Why does aluminium seem to not corrode?

Answer 9

• When corrodes forms protective layer of aluminium oxide – happens very quickly – when scratched will form layer again
• layer doesn’t allow air or water to pass through

Question 10

What is atom economy?

Answer 10

• amount of atoms wasted or lost when a chemical is made

Question 11

atom economy equation

Answer 11

atom economy = mass of atoms in desired product/ total mass of all products x100 – for percentage

Question 12

What is electroplating?

Answer 12

• acts as barrier to oxygen and water
• can electroplate a metal with an unreactive
  metal that is more attractive and will not corrode e.g. gold
• it’s done using the metal to be plated as cathode and metal you’re plating it with is the anode

Question 13

What is an alloy?

Answer 13

-a mixture of a metal w/ one or more other elements

Question 14

How does an alloy increase the strength of a product?

Answer 14

• have + ions of different metals, that have different sized ions– disrupts regular structure and stops ions being able to slide as easily, so leaves much
  harder, stronger metal.

Question 15

Why iron alloyed to make steel

Answer 15

• steals mixture of carbon and iron
• Low-carbon steels are malleable so used for sheeting
• High carbon steels are hard - used for cutting tools
• Stainless steels w/ chromium and nickel are resistant to corrosion - used for cutlery

Question 16

Uses of aluminium

Answer 16

low density, used for aircraft

Question 17

uses of copper

Answer 17

good conductor, used in electrical cables

Question 18

uses of gold

Answer 18

good resistance to corrosion, used in jewellery

Question 19

uses of magnalium

Answer 19

(aluminium + magnesium): low density, used in cars and planes

Question 20

uses of brass

Answer 20

(copper + zinc): hard, resistant to corrosion, used in coins

Question 21

calculate concentration (mol dm^-3)

Answer 21

concentration = no. of moles (mol) / volume (dm^3)

Question 22

Percentage yield equation

Answer 22

percentage yield = yield obtained/ predicted yield x 100

Question 23

What causes the actual yield being less than the predicted yield

Answer 23

• incomplete reactions
• practical losses during the experiment
• side reactions

Question 24

What is atom economy?

Answer 24

• amount of starting materials that end up as useful products

Question 25

atom economy equation

Answer 25

Relative molecular mass of desired product from reaction / sum of molecular mass (Mr) of all reactants

Question 26

Volume of gas at room temp. ( dm^3)

Answer 26

mol. x 24

Question 27

What is Avogadro's law

Answer 27

one mole of a substance contains 6.02 x 10^23 particles | - so if you had 10 moles of a substance, you'd do 10 x 6.02 x 10^23

Question 28

Benefits of atom economy

Answer 28

- Efficient processes have high atom economies, and are important for sustainable development, they use fewer natural resources and create less waste.

Question 29

What is the Haber process ?

Answer 29

- a reversible reaction between nitrogen and hydrogen to form ammonia using an iron catalyst at high temperature and pressure. - 200 atmospheres - 450 degrees temp.

Question 30

When is equilibrium reached at a faster rate

Answer 30

- higher temp. is used (particles have more kinetic energy so collide more frequently so have more successful collisions) - higher pressure/concentration is used (more particles in a given volume, so more frequent successful collisions) - catalyst is used - speed up rate of reaction

Question 31

How is the Haber process affected by cost of raw materials and other external factors

Answer 31

- a higher temp. shifts equilibrium towards the reactants forwards reaction is exothermic,compromise required to create a fast rate of reaction and a high yield of products - Catalyst can be expensive - High temp. and pressures can be expensive and dangerous and equipment required for them can be very expensive

Question 32

Describe how the Haber process works

Answer 32

- the purified gases (nitrogen and hydrogen) are passed over iron catalyst at high temp. (about 450 °C) and high pressure (about 200 atmospheres). - reaction mixture is then cooled and condensed into liquid and is used in fertilisers (fertilisers can contain nitrogen, phosphorus and potassium)

Question 33

How does ammonia react with nitric acid

Answer 33

-ammonia acts as a base ammonia + nitric acid -> ammonium nitrate - NH3 + HNO3 → NH4NO3

Question 34

production of ammonium sulphate in the industry

Answer 34

- reactants:are natural gas, air, water (to make ammonia) and sulphur, air, water (to make sulfuric acid) - on a large scale - are many stages required

Question 35

production of ammonium sulphate in a lab

Answer 35

- reactants are ammonia solution and dilute sulfuric acid (bought from chemical manufacturers) - on a small scale - involves a few stages

Question 36

describe what happens in a hydrogen-oxygen fuel cell

Answer 36

- Supplied by hydrogen and oxygen (or air) - reaction takes place within the fuel cell to produce a potential difference - Overall reaction in a hydrogen fuel cell involves the oxidation of hydrogen to produce water o 2H2 + O2 → 2H2O

Question 37

strengths of a fuel cell

Answer 37

- produce only water as waste -keep producing fuel if fuel keeps being supplied

Question 38

weaknesses of a fuel cell

Answer 38

- expensive to make | - difficult to transport/store hydrogen so aren’t suitable for portable devices

Question 39

What happens during a chemical cell

Answer 39

- chemical cells produce a voltage until one of the reactants is used up - Chemical reactions stop when one of the reactants has been used up