C5 - Monitoring and Controlling Chemical Reactions

Question 1

What is concentration?

Answer 1

Refers to how much particules there are in a fixed volume

Question 2

Equations for concentration:

Answer 2

Concentration (mol/dm^3) = moles / volume (dm^3)

or

Concentration (g/dm^3) = mass / volume (dm^3)

Question 3

How do you convert from cm^3 to dm^3?

Answer 3

Divide by 1000

Question 4

What are titrations used to find?

Answer 4

To find exactly how much acid is needed to neutralise a given quantity alkali

Question 5

Titration experiment steps:

Answer 5

1) Fill a clean, dry burette with acid
2) Note the starting volume of acid in the burette
3) In a clean, dry pipette transfer 25cm^3 of an alkali in conical flask
4) Add a few drops of indicator to the alkali in flask
5) While swirling regularly, slowly add the acid to the alkali
6) The indicator changes colour when all alkali has been neutralised - then stop adding the acid to the alkali
7) Record the volume of acid used to neutralise the alkali (the titre)
8) Repeat three more times and calculate the mean.

Question 6

What is the molar volume?

Answer 6

The volume occupied by one mole of gas

Question 7

General equation for molar volume:

Answer 7

Molar volume (dm^3/mol) = gas volume (dm^3) / number of moles

Question 8

What is the molar volume always in room temperature and pressure?

Answer 8

24dm^3/mol

-One mole of any gas at RTP (Room temperature or pressure) occupies 24dm^3 of space

Question 9

Equation for molar volume at RTP?

Answer 9

Volume of gas (dm^3) = 24dm^3/mol x Moles

Question 10

What is the percentage yield?

Answer 10

A percentage shows the overall success of the experiment compares what we expected to get (theoretical yield) and what we actual got (actual yield).

Question 11

Why is it hard to get 100% percentage yield?

Answer 11

Products can be lost by:

• Filtration
• Evaporation
• Transferring liquids

Question 12

What is the actual yield and theoretical yield?

Answer 12

Actual yield: The actual mass of products that were converted from reactants

Theoretical yield: The mass of products if all of the reactants had converted

Question 13

Equation for percentage yield:

Answer 13

Percentage yield(%) = 
(actual yield / theoretical yield) x 100

Question 14

What is atom economy?

Answer 14

Is the percentage of reactants changed to useful products

Question 15

Atom economy Equation?

Answer 15

Atom economy (%) = (Total Mr of desired products / total Mr of all Products) x 100

Question 16

Why is high atom economy beneficial?

Answer 16

• It is beneficial for profits and environment
  1) High atom economy makes these reactions sustainable (the don’t waste loads and produce lots of desired products so it doesn’t run out quickly)
  2) They are profitable (not lots of waste products). Raw materials are expensive to buy and rid of waste.

Question 17

What are factors considered in industry?

Answer 17

• Atom economy
• The percentage yield
• The rate of reaction. The rate of reaction must be fast enough to produce the amount of product you need in a sensible amount of time
• Whether the reaction is reversible. To keep the yield of a reversible reaction high, you might need to alter the reaction conditions, and doing this can be expensive.

Question 18

What is the rate of reaction?

Answer 18

The measure if how fast the reaction happens

Question 19

Mean rate of reaction equation:

Answer 19

Rate of reaction = amount of product formed / time

Question 20

What experiment to follow to find rate of reaction using precipitation?

Answer 20

-Use sodium thiosulphate and hydrochloric acid

1) Put a flask with thiosulphate in it on a piece of paper with a cross on it
2) Add hydrochloric acid and start stopwatch
3) Mix the two reactants
4) Observe how the long it takes for the cross to become obscure to see as a precipitate of sulphur. When you cannot see the cross anymore stop the stopwatch and that is the rate of reaction.

Question 21

What experiment to follow to find rate of reaction using change in mass?

Answer 21

1) Use a mass balance to see how much gas is produced and how quickly
2) Use a cotton wool as it lets gases escape but not solids, liquids or aqueous out.
3) As gas is produced from reaction, the lost mass is easily measured on the balance. The quicker the mass is lost the faster the rate of reaction

Question 22

What experiment to follow to find rate of reaction using the amount of gas given off?

Answer 22

1) Involves using a gas syringe to measure volume given off

2) The more gas given off in a set time, the higher the rate of reaction

Question 23

What is the experiment to show how surface area affects rate of reaction?

Answer 23

-Reaction of Hydrochloric acid and marble chip

1) Set up apparatus (flask and gas syringe)
2) Measure the volume of gas produced using a gas syringe in a specific amount of time
3) Do for large chips, small chips, powdered chalk and double quantity of small chips

Question 24

Expected results for the experiment showing how surface area affects the rate of reaction?

Answer 24

1) smaller chips means they have a higher surface area
2) The whole experiment shows how the smaller the object (higher surface area) leads to higher rate of reaction

3) The order of fastest rate of reaction to slowest ->
- DOUBLE QUANTITY OF SMALL CHIPS : Shows adding more chips, extra surface area and increases rate of reaction
- Then, POWDERED CHALK: smallest solid
- Then SMALL CHIP, next smallest solid
- LARGE CHIP, largest and has slowest rate of reaction

Question 25

How do we know rate of reaction on graph?

Answer 25

- The reaction has stopped when the line flatterns (rate of reaction is the amount of time for the reaction to finish) - The steeper the gradient the faster the reaction is (high amounts of product formed in short amount of time)

Question 26

How do you find the gradient of a curve?

Answer 26

- A curve means the rate of reaction changes at different points - To find gradient of a certain point, draw a tangent to the curve at that point - Find the gradient of the tangent

Question 27

Equation for working out rate of reaction?

Answer 27

Rate of reaction = 1 / time Rate of reaction indirectly proportional to time. As time increases = rate of reaction decreases As time decreases = rate of reaction increases EG. If a reaction takes 86 seconds to stop, the rate of reaction will be 1/86.

Question 28

What is the collision theory?

Answer 28

- Reactions occur when particles collide with each other with enough energy. - The more frequent the collision, the higher the rate of reaction

Question 29

Factors affecting the rate of reaction?

Answer 29

1) Volume 2) Concentration 3) Temperature 4) Surface area (size of particles)

Question 30

How does volume affect the rate of reaction?

Answer 30

- When volume is decreased, particles have less space, leading to more frequent collision, higher rate of reaction - When volume increased, particles have more space, less frequent collision, lower rate of reactions

Question 31

How does concentartion affect the rate of reaction?

Answer 31

- Higher concentration, particles more crowded, more frequent collisions, higher rate of reaction - Lower concentration, particles less crowded, less frequent collisions, lower rate of reaction

Question 32

How does Temperature affect the rate of reaction?

Answer 32

- Higher rate of reaction, particles have more kinetic energy, more frequent collisions with more force, rate of reaction increase - Lower rate of reaction, particles have less kinetic energy, less frequent collisions, lower rate of reaction

Question 33

How does size of particles affect the rate of reaction?

Answer 33

- Decreasing particle size there is more surface area the collision can take place on, higher rate of reaction - increasing particle size there is less surface area the collision can take place on, lower rate of reaction

Question 34

What are catalysts?

Answer 34

A substance that increases the rate of reactions without being chemically changed or used up in the end

Question 35

How do catalyst work?

Answer 35

They lower the activation energy (the energy required for a chemical reaction to start) by providing a alternate route for reaction to follow which has a lower activation energy

Question 36

What is the relationship between concentration and rate of reaction?

Answer 36

Directly proportional: HIgher the concentration the higher the rate of reaction

Question 37

What is the relationship between concentration and time?

Answer 37

Indirectly proportional: Higher the concentration the less time for reaction to stop