Separate Chemistry I

Question 1

What are some transition metal properties? (5)

Answer 1

1. High melting point (due to electrostatic forces of attraction between positively charged metal ions and ‘sea’ of electrons).
2. High density
3. They have ions with many different charges.
4. Form coloured compounds.
5. Are useful as catalysts - its used in the Haber process as a catalyst.

Question 2

How does oxidation of metals result in corrosion?

Answer 2

Rusting - Both air and water are necessary for iron to rust – i.e. oxidation – gain of oxygen results in corrosion.

Question 3

How can rusting of iron be prevented?

Answer 3

Rusting can be prevented by excluding oxygen and water e.g. by:
Painting
Coating with plastic
Using oil or grease
Aluminium has an oxide coating that protects the metal from further corrosion – exclusion of oxygen and water.
Water can be kept away using a desiccant in the container (absorbs water vapour).
Oxygen can be kept away by storing the metal in a vacuum container.

Question 4

What is Sacrificial protection?

Answer 4

Where the metal you want to be protected from rusting is galvanised with a more reactive metal, which will rust first and prevent water and oxygen reaching the layer underneath - E.g. zinc is used to galvanise iron.

Question 5

How can electroplating be used to improve the appearance and resistance to corrosion of metal objects?

Answer 5

Electroplating acts as a barrier in order to exclude oxygen and water.
Also improves appearance as you can electroplate a metal with an unreactive metal such as gold that is more attractive and will not corrode.
It is done using the metal to be plated as the cathode and the metal you’re plating it with as the anode, then have a solution containing ions of the metal being used to do the plating.

Question 6

Explain why converting pure metals into alloys often increases the strength of the product

Answer 6

Most metals in everyday uses are alloys.
Pure copper, gold, iron and aluminium are all too soft for everyday uses and so are mixed with small amounts of similar metals to make them harder for everyday use.
This works because in a pure metal, all the + metal ions are the same size and in a regular arrangement, allowing the layers to slide over each other relatively easily, making the metal soft and malleable. In an alloy, you have + ions of different metals, which have different sized ions. This disrupts the regular structure and prevents the ions being able to slide as easily, leaving a much harder, stronger metal.

Question 7

Why is iron alloyed with other metals to produce alloy steels?

Answer 7

Steels are alloys since they used mixtures of carbon and iron.
Some steels contain other metals. Alloys can be designed to specific uses.
Low-carbon steels are easily shaped - used for sheeting (malleable).
High carbon steels are hard - used for cutting tools.
Stainless steels (containing chromium and nickel) are resistant to corrosion - used for cutlery.

Question 8

How the uses of metals are related to their properties:
Aluminium
Copper
Gold
Magnalium (aluminium + magnesium)
Brass (copper + zinc)

Answer 8

Aluminium: low density, used for aircraft
Copper: good conductor, used in electrical cables
Gold: good resistance to corrosion, used in jewellery
Magnalium (aluminium + magnesium): low density, used in cars and planes
Brass (copper + zinc): hard, resistant to corrosion, used in coins

Question 9

How to calculate the concentration of solutions in mol dm-3?

Answer 9

Conc = Mol/vol

Question 10

CORE PRACTICAL - Carry out an accurate acid-alkali titration (6)

Answer 10

1. Add acid to burette using a funnel, record the volume in the burette to start.
2. Add known volume of alkali to a conical flask and add some indicator.
3. Place conical flask on white tile (so you can see colour change clearly).
4. Add acid to alkali until you reach the end point.
5. Calculate how much acid has been added (titre).
6. Repeat until you get concordant titres.

Question 11

How to calculate the percentage yield?

Answer 11

Percentage yield = (Amount of product produced-actual yield / Maximum amount of product possible-theoretical yield) X 100

Question 12

Describe the term “yield”

Answer 12

Amount of product obtained.

Question 13

What are the causes of actual yield being less than theoretical yield? (3)

Answer 13

1. Incomplete reactions (not all of the reactants have reacted).
2. Practical losses during the experiment (some product has been left in the weighing boat etc).
3. Side reactions (some of the products react to form other products than those you wanted).

Question 14

Suggest a reason why the actual yield can be greater than the theoretical yield

Answer 14

Not all the water has been evaporated off.

Question 15

What is atom economy?

Answer 15

A measure of the amount of starting materials that end up as useful products.
(Mr of desired product from reaction / sum of Mr of all reactants) x 100

Question 16

Why is atom economy important?

Answer 16

Important for sustainable development and for economic reasons to use reactions with high atom economy.

Question 17

Explain why a particular reaction pathway is chosen to produce a specified product?

Answer 17

It has a high atom economy, high yield, fast rate, equilibrium position to the right (towards products) and useful by-products.

Question 18

Describe the molar volume

Answer 18

Volume (dm3 ) of gas at RTP = Mol. x 24
Volume (cm3 ) of gas at RTP = mol x 24,000

Question 19

What is avogadro’s law to calculate volumes of gases?

Answer 19

6.02 x 10^23 particles

Question 20

What are the conditions for the haber process? (3)

Answer 20

1. High temperature (about 450 °C)
2. High pressure (about 200 atmospheres)
3. Iron Catalyst

Question 21

Predict how the rate of attainment of equilibrium is affected by: changes in temperature

Answer 21

Increasing the temperature will lead to all the molecule having more energy, an so they will collide more frequently. Both the forward and backward reactions will occur faster and so therefore equilibrium is reached faster.

Question 22

Predict how the rate of attainment of equilibrium is affected by changes in pressure

Answer 22

Increasing the pressure will lead to all gaseous molecules being closer together, and so they will collide more frequently. Both the forward and backwards reaction will occur faster.

Question 23

Predict how the rate of attainment of equilibrium is affected by changes in concentration

Answer 23

Increasing the concentration will lead to there being more particles per litre and so they will collide more frequently. Both the forward and backward reactions will occur more faster, and therefore equilibrium will be reached faster.

Question 24

Predict how the rate of attainment of equilibrium is affected by using a catalyst

Answer 24

Adding a catalyst, reduces the activation energy of both the forward and backward reactions, which will therefore occur faster, and therefore equilibrium will be reached faster.

Question 25

What are fertilisers used for?

Answer 25

Compounds of nitrogen, phosphorus and potassium are used as fertilisers to improve agricultural productivity.

Question 26

Describe how ammonia reacts with nitric acid to produce a salt that is used as a fertiliser

Answer 26

Ammonia can be used to manufacture ammonium salts with nitric acid. Ammonia acts as a base.
ammonia + nitric acid → ammonium nitrate

Question 27

Describe and Compare:
The laboratory preparation of ammonium sulfate from ammonia solution and dilute sulfuric acid on a small scale:
The industrial production of ammonium sulfate, used as a fertiliser:

Answer 27

Reactants: ammonia solution and dilute sulfuric acid (bought from chemical manufacturers).
SMALL scale (very little is produced).
Only involves a few stages (titration then crystallisation).

Reactants: natural gas, air, water (to make ammonia) and sulfur, air, water (to make sulfuric acid).
LARGE scale (produces a lot).
Many stages required (need to make ammonia and sulfuric acid, react accurate volumes then evaporate).

Question 28

What are chemical cells?

Answer 28

Chemical cells no longer produces voltage when the reactants are used up, and so the chemical reactions stop.

Question 29

What are hydrogen-oxygen fuel cells?

Answer 29

Supplied by an external source of fuel (eg hydrogen) and oxygen or air.
The 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.
2H2 + O2 → 2H2O

Question 30

What are some strengths for fuel cells? (2)

Answer 30

1. Produce only water as waste.
2. Keep producing fuel if fuel keeps being supplied.

Question 31

What are some problems with fuel cells? (2)

Answer 31

1. Difficult to transport/store hydrogen so aren’t suitable for portable devices.
2. Expensive to make.