Theory Important

Question 1

Define Fossil Fuels?

Answer 1

A fuel that has been produced over a long period of time by the breakdown of organic material, such as decaying remains of plants and tiny marine animals. Fossil fuels are non-renewable because they are used faster than they can be replenished

Question 2

Define difference between Renewable and Non-Renewable Fuel?

Answer 2

Renewable fuel is made from decomposition of biomass can be replenished as fast as it is consumed whereas non-renewable fuel is made from fossil fuels and cannot be replenished as fast as it consumed

Question 3

Explain the carbon neutrality of Biofuels?

Answer 3

Biofuels are more carbon neutral than Fossil fuels, as during their combustion, plants remove CO2 released by biofuels for the purpose of photosynthesis

Question 4

Define Activation Energy?

Answer 4

Activation energy is the minimum energy required to break the bonds between atoms of reactants and initiate the reaction

Question 5

What is the purpose of salt bridge?

Answer 5

The salt bridge contains ions that free to move so they can balance the charges formed. Cations to move to the cathode and anions move to the anode, creating the internal circuit

Question 6

What is the purpose of half cell?

Answer 6

To keep the reactants separate the prevent a spontaneous redox reactions. Thus, enable the flow of electrons to transfer via the external circuit

Question 7

Why are Electrolytes usually in the form of a paste or gel, not a dilute solution?

Answer 7

Increases concentration of electrolyte, increasing the rate of reaction. Therefore, battery last longer, takes longer to reach equilibrium/polarisation

Question 8

Why is a separator is used instead of a salt bridge. Why can it be a gelled electrolyte, a microporous plastic film or a porous inert material filled with electrolyte?

Answer 8

Separates the reactants but allows the ions in electrolyte to migrate to the electrodes. Cations join the cathode and the anions join the anode.

Question 9

Why the anode and cathode are separated by an insulator?

Answer 9

Heat is also a product. Thus, insulator minimises the heat loss and reduces the efficiency and extends battery life

Question 10

Why possible products of electrode reactions are removed from the electrode surfaces?

Answer 10

By removing products from electrode, thus products no longer build up. Therefore, it takes longer to reach equilibrium polarisation and equilibrium last longer

Question 11

Describe two important functions of electrodes in this cell?

Answer 11

Porous electrodes allow reactants gases to diffuse slowly through, thus they can catalyse the reaction. Thus, it is the site of oxidation and reduction. They also keep reactants separate and thus, ensuring spontaneous redox reaction does not occur

Question 12

Explain why the energy released when food is heated is greater than the energy available to the body?

Answer 12

This is due to incomplete absorption of nutrients by the body after digestion of food and incomplete oxidation of nutrients

Question 13

A known mass of food is dried thoroughly and then burnt in the bomb calorimeter. Why must the food be dried?

Answer 13

To ensure excess water is removed before heating (otherwise heat will be wasted evaporating water rather than combusting food)

Question 14

Explain why lipids are insoluble in water?

Answer 14

• Lipids are a large, non-polar molecule with long hydrocarbon tail
• Even though they have an ester functional group which can form a hydrogen bond with water it is predominantly a large non-polar molecule and so insoluble in water as it can only form dispersion forces

Question 15

Explain how the strength of the forces between molecules is different between fat molecules and oil molecules?

Answer 15

• Saturated fats - solids - due to the ability of the trigs to pack closely together thus they have greater dispersion forces -> higher melting point -> solids at room temp
• Unsaturated fats (oils) - due to the presence of the C=C bonds this causes the fatty acid chains to kink -> thus the molecules are unable to pack as closely together -> decreases strength of the dispersion forces ->low melting point

Question 16

Monosaccharides contain -OH functional groups and so can form hydrogen bonds with water. Why is the solubility of glucose in water important to biological processes?

Answer 16

• Due to many -OH functional groups, they can form hydrogen bonds with water
• Thus they are also very insoluble in water
• Therefore digest easily
• As a result, can be easily metabolised

Question 17

Explain why polysaccharides are significantly less soluble than disaccharides or monosaccharides?

Answer 17

Polysaccharides are made up of long chains of monosaccharide linked -C-O-C bonds. Cross links form between chains too. Therefore, there are no available OH groups to forms H-bonds with water.

Question 18

Why is amylose, slower to digest?

Answer 18

Due to the many exposed polar -OH functional groups - many hydrogen bonds can be formed between the monomers. Thus the straight chain tightly coils - causing many of the -OH functional sites to be internally facing thus decrease in solubility in water. Therefore, fewer Hydrogen bonds can be formed and as a result is slower to digest due to inability to break down monomers.

Question 19

Why is amylopectin, easier to digest?

Answer 19

Amylopectin is a branched polymer- thus there are many the -OH functional sites exposed as it
doesn’t coil. Thus it can easily form H bonds with water, very soluble and thus, easy to digest.

Question 20

How would a decrease from optimum temperature influence enzyme activity?

Answer 20

decrease in temp will decrease the rate of successful collisions thus decrease ROR but has no effect on the IMF within the enzyme thus no effect on the 3D structure thus no effect on the active site - enzyme does not denature - inactive.

Question 21

How would a increase from optimum temperature influence enzyme activity?

Answer 21

Increase in temperature above optimal, will disrupt the hydrogen bonds between the amide links in the secondary structure and between the R groups in the tertiary structure thus the protein will unravel, new bonds form, 3D will change, there will be a change in the shape of active site and the substrate will no longer be able to bind to the active site and enzyme cannot catalyse reaction / denatured

Question 22

How would a change from pH impact enzyme activity?

Answer 22

any change in pH from optimal pH range - can cause the acidic or alkaline R groups in the tertiary structure to ionise, as a consequence the ionic, Hydrogen and ion-dipole bonds can break, the enzyme will unravel, new bonds between R groups will form and 3D will change, there will be a change in the shape of active site and the substrate will no longer be able to bind to the active site and enzyme cannot catalyse reaction / denatured

Question 23

Explain why denaturation has no effect on the primary structure of a protein?

Answer 23

• Because the change in pH or temperature is not significant enough to break the covalent amide link between the amino acids that form the primary structure

Question 24

Amylopectin is digested more rapidly than amylose. With reference to their structures, and hence their solubilities in water, explain this property?

Answer 24

• Amylose -> straight chain polysaccharide-> forms a tight coil due to strong hydrogen bonds between the -OH functional groups -> thus - OH groups are internally facing -> decreases the solubility of amylose in water -> harder to hydrolyse -> slower to digest - > harder for the enzyme catalyse the reaction
• Amylopectin -> branched polysaccharide -> -OH groups are exposed-> can form hydrogen bonds with water -> increases solubility in water -> easier to hydrolyse -> digest faster-> easier for the enzyme to catalyse the hydrolysis

Question 25

Are triglycerides soluble or insoluble in water

Answer 25

Triglycerides are insoluble in water - even though there are 3 ester functional groups the molecule is overall non polar thus cannot form hydrogen bonds with water thus insoluble in water

Question 26

Explain hydrolysis of triglycerides

Answer 26

Triglycerides are hydrolysed - after they are emulsified with bile - increase the surface are of fats by breaking down into water soluble droplets -> thus enabling the water and enzyme to act on them and catalyse the hydrolysis of triglycerides

Question 27

Explain why the energy released when food is heated is greater than the energy available to the body?

Answer 27

• Energy oxidation in a lab in excess - 100% combustion. In humans - not have 100% digestion & absorption of all nutrients, not have 100% oxidation of the nutrients in the human body, thus we do not get all the KJ available

Question 28

Describe the bonding that is found in the primary and secondary structures of the glucagon molecule?

Answer 28

• Primary structure (covalent bonds between C and N in the peptide links between amino acids
• Secondary structure – hydrogen bonds between O (-C=O) AND H (-N-H) on different peptide groups in the a-helix (B-sheet)

Question 29

Explain enzyme lock and key model?

Answer 29

The reactant molecules manoeuvre into the active site and once bound here, the reaction can occur, and new product/s are released. Once in the active site, the substrate is held by a variety of bonds. These bonds can include:

• Hydrogen bonding
• Dipole-dipole
• Dispersion forces
• Electrostatic attraction between groups of atoms of opposite charge
• Ion-dipole interactions
2. The substrate bound to the enzyme is called the enzyme-substrate complex. The existing bonds within the substrate are weakened due to the new bonds formed between the substrate and the enzyme’s active site. This lowers the activation energy for the reaction.

3. The enzyme-substrate complex then breaks down to release the products of the reaction. The enzyme, like all catalysts, remains unchanged by the reaction and is able to catalyse the same reaction with new substrate particles.

Question 30

Why can’t humans digest cellulose?

Answer 30

Cellulose is condensation polymer of beta glucose. Humans cannot digest cellulose because we lack the enzyme cellulase - thus cannot metabolise cellulose thus NO beta glucose

Question 31

Why is fat the main method of storing energy in the body?

Answer 31

Fat has a much greater energy content than carbohydrates or proteins so is a more efficient storage of energy

Question 32

Describe briefly 3 steps in the process of digestion and adsorption of triglycerides in the small intestine?

Answer 32

1. Bile emulsifies fats and oils which increases reactive area
2. Lipase hydrolyses the three ester bonds of a triglyceride into 3 fatty acids and a glycerol molecule
3. Fatty acids and glycerol pass into the bloodstream

Question 33

Describe briefly where triglycerides are stored in the body, and how they can be used for energy production?

Answer 33

Initially triglycerides are re-formed in the liver from fatty acids and glycerol through condensation reactions.

• Excess triglycerides are stored in adipose tissue.
• Energy production is by oxidizing the fatty acids

Question 34

How increase in concentration impacts rate of reaction?

Answer 34

increase in concentration will increase the number of particles per unit of volume. This will increase the frequency of collisions. Therefore, this increases the frequency of successful collisions which lead to an increase in rate of reaction

Question 35

How increase in surface area impacts rate of reaction?

Answer 35

– an increase in surface area per volume results in an increase in the number of particles available to react. This will increase the frequency of collisions. Therefore, the increase in the frequency of successful collisions which leads to an increase in rate of reaction

Question 36

How increase in temperature impacts rate of reaction?

Answer 36

increases in temperature will increase the average kinetic energy of the particles. Therefore, the increase in proportion of particles will have the minimum required activation energy. This will increase the frequency of successful collisions which increase the rate

Question 37

How increase in catalysts?

Answer 37

Catalyst will provide an alternate pathway with a lower activation energy. Therefore the increase in proportion of particles will have the required activation energy

Question 38

Describe Homogenous vs Heterogeneous Equilibria?

Answer 38

• A homogeneous equilibrium has everything present in the same phase. The usual examples include reactions where everything is a gas, or everything is present in the same solution
• A heterogeneous equilibrium has things present in more than one phase. The usual examples include reactions involving solids and gases, or solids and liquids

Question 39

Define a standard solution?

Answer 39

A solution with an accurately known concentration

Question 40

Why is the Rf values always less than 1?

Answer 40

The distance of the samples cannot surpass the distance of the solvent front

Question 41

Distinguish between the terms Separation and Resolution in a chromatographic analysis?

Answer 41

Separation represents separated peaks in a chromatogram whereas resolution represents the difference between retention times of the substances

Question 42

What is the relationship between the length of the carbon chain and boiling point? Explain?

Answer 42

The longer the carbon chain, the higher the boiling point, as the more carbon and hydrogen atoms there are, the greater the dispersion forces

1. As hydrocarbons are non-polar they have only intermolecular dispersion forces
2. The longer the carbon chain, the more C-H atoms there are resulting is greater dispersion forces
3. Stronger dispersion forces, the higher boiling point

Question 43

Why can’t tertiary alcohols be oxidised?

Answer 43

Tertiary alcohols are resistant to reaction with strong oxidising agent. In tertiary alcohols, the carbons attached to the -OH group does not have a C-H bond to break so oxidation cannot occur at the carbon atom