Topic 6 - Analysis And Fuels

Question 1

What is theoretical yield and actual yield?

Answer 1

Theoretical - estimated amount from balanced equation

Actual - Actual amount obtained when you carry out experiment

Question 2

How do you figure out percentage yield?

Answer 2

Actual yield / theoretical X 100

Question 3

What are 3 reasons why the actual yield isn’t 100%?

Answer 3

Reaction may not be incomplete so not all of reactants are used up

Some of product is lost when transferring from one container to another

There may be unwanted side reactions taking place

Question 4

What does a higher percentage yield mean?

Answer 4

The more useful the reaction is

Question 5

How do you calculate atom economy?

Answer 5

RFM of useful product / RFM of all reactants X 100

Question 6

When is atom economy 100%?

Answer 6

When all the atoms in the reactants are present in product

Question 7

Why can atom economy be less than 100?

Answer 7

When things are made/formed as by-products

Question 8

What are the raw materials, temperature and pressure of fermentation?

Answer 8

Carbohydrates (e.g. sugar) these are renewable

Temperature = 30-40 degrees

Pressure = atmospheric

Question 9

What is the catalyst, rate of reaction and purity of fermentation?

Answer 9

Catalysts are enzymes in yeast

Rate of reaction is slow

It is impure (must be fractionally distilled)

Question 10

What are the raw materials, temperature and pressure for the reaction of Ethene with steam?

Answer 10

Raw materials = Ethene obtained from crude oil (non renewable)

Temperature = 300 degrees

Pressure = High pressure

Question 11

What are the catalysts, rate of reaction and purity for reaction of steam with Ethene?

Answer 11

Catalyst = concentrated phosphoric acid

Rate of reaction = fast

Purity = pure

Question 12

How do you calculate concentration?

Answer 12

Mass of solute / volume of solution

Question 13

How do you calculate concentration using moles?

Answer 13

Number of moles / volume of solution

Question 14

How do you calculate concentration (moles) using the other concentration equation?

Answer 14

Concentration in mol =

Concentration in g dm / Rfm of solute

Question 15

What is the Core Practical for titration?

Answer 15

Rinse burette with HCl, then close tap and fill the burette with HCl, making sure tap is full.
Record initial volume of acid in burette
Rinse a pipette with sodium hydroxide solution, then fill the pipette to 25cm cubed and empty this into the conical flask
Add a few drops of phenylalanine to flask and put flask onto white tile
Add the acid to flask which swirling the flask
Add the acid until the solution begins to change colour and then add it drop by drop until the solution turns pink
Record the final volume of acid in burette
Repeat experiment until a set of concordant results is gained

Question 16

What is the molar volume of gas?

Answer 16

24dm cubed

Question 17

How do you calculate the amount of gas?

Answer 17

Volume of gas / 24dm cubed

Question 18

How would you solve this question:

Calculate the minimum mass of copper carbonate needed to produce 1.44 of carbon dioxide?

Answer 18

Amount of carbon dioxide = volume / 24 = 1.44/24 = 0.06
Mass of copper carbonate = mol x Rfm
= 0.06 x 123.5 = 7.41

Question 19

How do you calculate number of molecules?

Answer 19

Moles x Avogadro constant

Question 20

How do you calculate the maximum volume of another element?

Answer 20

Figure out moles of 1st and then times moles by 24

Question 21

What are fertilisers?

Answer 21

They replace the mineral ions needed by plants so they promote plant growth

Question 22

What are nitrogenous fertilisers and give an example?

Answer 22

Sources of soluble nitrogen compounds

E.g. ammonium nitrate

Question 23

Hw do you make ammonium sulfate?

Answer 23

Reacting ammonia solution with dilute sulfuric acid

Question 24

What is laboratory preparation?

Answer 24

Small scale
Starting materials: ammonia solution and dilute sulfuric acid
Stages: titration then crystallisation
Type of process: batch

Question 25

What is industrial production?

Answer 25

Large scale
Starting materials: raw materials for making ammonia and sulfuric acid
Several stages
Continuous process

Question 26

What is a batch process?

Answer 26

A small amount is made, the apparatus is cleaned and then another small amount is made

Question 27

What is a continuous process?

Answer 27

Where reactants are constantly fed into the reactors and products are removed 
Rarely stopped (even then its to clean and maintain equipment) 
Need fewer people

Question 28

How do you decrease the time taken to reach equilibrium?

Answer 28

Increase the temperature
Increased the pressure
Increase the concentration of the reacting substance
Add a catalyst

Question 29

What do all chemical manufacturers want to make?

Answer 29

A profit - an increased yield

Question 30

Why is a temperature of 200 degrees used in the Haber process?

Answer 30

High pressures increase the equilibrium yield of ammonia and increase the rate of reaction
The pressure isn’t too high as high pressures are too expensive to maintain so the 200 atmospheres is a compromise

Question 31

Why is a temperature of 450 degrees used in the Haber process?

Answer 31

Forward reaction is exothermic and backwards reaction is endothermic
When temperature increases, the position of equilibrium moves to left (in direction of endothermic reaction)
Low temperatures increase the equilibrium yield of ammonia but reduce the rate of reaction
The temperature chosen 450 degrees is a compromise that gives an acceptable yield in an acceptable time

Question 32

Why is an iron catalyst used in the Haber process?

Answer 32

It doesn’t change the position of equilibrium but it does increase the rate of reaction

Question 33

What do you have to take into account when choosing a reaction pathway?

Answer 33

Availability and cost of raw materials and energy supplies
The rate of reaction and the equilibrium position
Atom economy and yield and usefulness of by-products

Question 34

How was nitric acid made in the past?

Answer 34

Used high voltages between electrodes with nitrogen and oxygen reacting in air to form nitrogen monoxide then further reacted with oxygen to make nitrogen dioxide which was dissolved in water to form nitric acid
This used huge amounts of electricity and only made a very small yield

Question 35

What components does a chemical cell have?

Answer 35

Two different metals, each dipped into a solution of one of their salts
A salt bridge to allow dissolved ions to pass from one solution to the other

Question 36

What creates the greater voltage?

Answer 36

The further apart in the reactivity series the two metals are

Question 37

When will a current flow?

Answer 37

If the cell is connected to an external circuit

Question 38

How is energy usually transferred?

Answer 38

Mainly by electricity than heating

When one of the reactants is used up, the reaction stops and a voltage is no longer produced

Question 39

What are fuel cells?

Answer 39

Cells supplied with fuel and oxygen from outside

They produce a voltage for as long as reactants are supplied

Question 40

What is a benefit of hydrogen-oxygen fuel cell?

Answer 40

They are much quieter and need less maintenance than petrol/Diesel engine
Hydrogen still needs to be stored in a tank

But it doesn’t produce carbon dioxide
However, most hydrogen is manufactured by the reaction of steam with coal/natural gas
These processes do release carbon dioxide as a by-product