CHAPTER 12
REVIEW QUESTIONS
12.1
It has an equal number of positively charged protons and negatively charged electrons.
12.2
It becomes filled with electrons and thus the molecule becomes stable.
12.3
In both ionic and molecular compounds, the outer energy levels of the constituent atoms
become filled and so the molecule is stable. Ionic compounds are formed when atoms lose (and
become positively charged) or gain (and become negatively charged) electrons to form ions.
The ions are then attracted to each other by electrostatic forces to form a stable compound. In
molecular compounds atoms share electrons in the formation of the compound.
12.4
There are three molecules of water. Thus there are 6 hydrogen atoms and 3 water atoms
making a total of 9 atoms.
12.5
Both mixtures are composed of two or more chemicals. In homogenous mixtures the different
types of molecules are evenly dispersed, forming a solution, whereas in heterogeneous
mixtures the molecules are unevenly dispersed and form either a colloidal or insoluble
suspension.
12.6
In a solution the solute particles are small and easily dispersed by Brownian motion and so
form a homogenous mixture which is transparent. The solute particles in a colloidal suspension
are too large to be evenly dispersed by Brownian motion and tend to be suspended in clumps
within the solvent (heterogenous mixture) and have a cloudy to opaque appearance. Insoluble
suspensions are formed when the particles of one substance are so large that they cannot be
dispersed by Brownian motion and they settle to the bottom of the liquid.
12.7
Brownian motion is caused by the buffeting action of freely moving fluid molecules on solid
particles suspended in them.
12.8
Hydrogen chloride is an ionic compound which separates into its component ions in solution.
Since there are more hydrogen ions than hydroxide ions present in the solution, it is acidic.
12.9
The solution with pH 2 is more acidic than that with a pH of 6 since the lower the pH value the
greater the hydrogen ion concentration.
12.10
The ability of substances to dissociate to release hydrogen or hydroxide ions in solution.
12.11
There is an uneven distribution of charge on the molecule. Because oxygen is a larger atom
than hydrogen, its force of attraction for the shared electrons is greater than that of hydrogen.
Thus electrons are pulled towards oxygen giving it a slightly negative charge and leaving a
slightly positive charge on the two hydrogen atoms.
12.12
Although they exert a force of attraction between charged molecules, hydrogen bonds are not
as strong as ionic bonds.
12.13
Water is polar, producing strong forces of cohesion.
It is a good solvent.
Water has a very high heat capacity.
Water has a high latent heat of vaporisation and fusion.
Water molecules have a high surface tension and display cohesion and adhesion.
Water is neutral.
Water increases in volume and decreases in density between 4o and 0oC.
12.14
The polarity of water is responsible for its forces of cohesion resulting in a high surface tension
and increasing the dispersal of solutes by Brownian motion, making water a good solvent. The
high heat capacity of water and its high latent heat of vaporisation is related to the amount of
energy required to break the hydrogen bonds between water molecules.
12.15
An antifreeze is a chemical which depresses the freezing point of a liquid.
12.16
Birds and mammals are endothermic and able to control their body temperature by
physiological means. Thus they are able to remain active under very cold conditions so long as
they have adequate food and water to produce energy from respiration, Fish are ectothermic
and cannot control their body temperature in this way. Thus their body temperature fluctuates
with environmental temperature. Since the waters of Antarctica are extremely cold, few fish
have adaptations which allow them to remain active at these temperatures.
12.17
They are in very cold water and any body heat, required for maintenance of life, can readily be
lost to the surroundings by conduction.
12.18
Their body fluids contain antifreeze substances – salts and glycoproteins – which depress the
freezing point to -2.2°C.
12.19
Since it can form covalent bonds with up to four other elements, including another carbon, a
large number of macromolecules, with different structures and functions and which store large
amounts of chemical bond energy, can be formed.
12.20
Carbon can form covalent bonds with other carbon atoms.
12.21
An unsaturated carbon compound contains one or more multiple carbon-carbon bonds which
can be changed by the addition of further atoms, whereas a saturated carbon compound only
has single carbon-carbon bonds and so cannot add further atoms to its structure.
12.22
A macromolecule is a large carbon compound composed of repeating units or monomers of
that substance.
12.23
When two monomers join, a hydrogen atom from one molecule and a hydroxide group from
the other are removed, creating a bond between the two monomers and thereby releasing a
water molecule. This process is called dehydration synthesis or condensation.
12.24
Hydrolysis: water and an enzyme specific for the reaction are required.
12.25
Monomers: CnH2nOn
12.26
a.
b.
12.27
They are isomers and have different structural formulae. Thus different atoms or groups of
atoms will be exposed, giving them different physical and chemical properties.
Polysaccharides: (C6H10O5)n + H2O
Disaccharide.
Dehydration synthesis.
12.28
R
H
O
N
H
amino group
12.29
C
C
H
OH
carboxyl group
R is a variable group
They all contain an amino group at one end of the molecule and a carboxyl group at the other
end. The central group contains a variable R group which may consist of one or more atoms.
This R group gives the amino acid its specific properties. Thus each of the twenty different
amino acids has a characteristic R group.
12.30
A polypeptide chain is a straight chain of many amino acids each linked by a peptide bond. A
protein is formed when this polypeptide chain folds due to interactions between different
amino acids along its length.
12.31
Heating the protein has caused it to irreversibly lose its specific three-dimensional shape. The
protein has become denatured.
12.32
a.
b.
The protein but not lipid has an amino group, although both have a carboxyl group and
variable R groups.
There is no set proportion of carbon, hydrogen and oxygen in a lipid but there is in a
carbohydrate.
12.33
Three fatty acids independently form an ester bond with an OH group on the glycerol
molecule, thus releasing three water molecules.
12.34
B: an amino acid or fatty acid. Both amino acids and fatty acids contain a carboxyl group.
12.35
Phosphate, a sugar and a base.
12.36
A strand of DNA is composed of two chains whilst that of RNA is a single chain.
The sugar in DNA is deoxyribose and that of RNA is ribose.
The base thymine of DNA is replaced by uracil in RNA.
12.37
DNA is involved in the transmission of genetic information from one generation to the next
and in controlling the action of the cell through protein synthesis. RNA is involved in the
translation of the genetic code into protein production by the cell.
12.38
a.
b.
c.
d.
A: base. B: sugar. C: phosphate.
Adenine.
By hydrogen bonds.
12.39
First Law of Thermodynamics: energy cannot be created or destroyed but can be changed from
one form to another. Thus radiant energy can be converted to chemical bond energy in
photosynthesis. This energy can be released during respiration to provide energy for life
processes. Some of the energy, however, is converted to heat energy and released into the
atmosphere.
The Second Law of Thermodynamics: every energy transformation results in a reduction of the
useable or free energy of the system, and this results in a general tendency towards greater
disorder. Thus, in order for living systems to retain their ‘order’ they must constantly replenish
their energy supplies.
12.40
All chemical reactions are initiated by an input of energy (activation energy), the amount
determined by the type of reaction, the temperature of the reaction, concentration of substrates
and presence or absence of a catalyst.
12.41
Chemical reactions only take place if the reactants collide, thus any factor which increases the
chance of collision will determine if, and at what rate, the reaction will occur.
12.42
pH and substrate concentration.
12.43
a.
b.
They are globular proteins which increase the rate of chemical reactions without being
used up in the reaction. Their presence does not alter the nature of the end products of the
reaction. A small amount of enzyme catalyses a large quantity of substrate. They are
specific in their action which they can catalyse in either direction depending on substrate
concentration. They reduce the amount of activation level required for the reaction. Each
enzyme operates at an optimum temperature and pH. As the concentration of either
substrate or enzyme increases, so does the rate of reaction up to a maximum level.
Enzymes can be inhibited by poisons.
Each enzyme has an active site, the shape and size of which allows it to interact with a
specific substrate. At the active site the substrate molecules are rearranged (chemical
reaction) to form products, which now have a different shape and no longer fit the active
site. They are therefore released by the enzyme. Thus the enzyme acts as a lock and the
substrate a key.
12.44
In competitive inhibition the poison either competes for the substrate or the active site on the
enzyme. In non-competitive inhibition the poison permanently blocks the active site of the
enzyme.
12.45
The amino acids.
12.46
The amino acids.
12.47
The reaction can take place in either direction.
12.48
Enzyme A acts as the lock for the amino acids (the key). The enzyme activates the formation
of the dipeptide and water which are then released. In a similar way Enzyme B activates the
reaction between the dipeptide and water to release the two amino acids.
12.49
Each enzyme has an active sites, the shape and side of which only allows it to interact with
specific molecules.
12.50
B: differ in composition and shape.
12.51
ATP is composed of an adenosine unit and three phosphate groups arranged end to end. The
last two phosphate groups are attached by bonds which are very weak and unstable. When each
is broken the free phosphate can react with another molecule and form more stable bonds,
releasing large amounts of energy. Thus removal of one or two phosphates from ATP results in
the release of energy which can be used by the cell to do work. Addition of phosphate to AMP
or ADP results in the storage of energy. Since ATP is a small molecule it is easily transported
from a site of formation to a site where energy is required.
12.52
A metabolic reaction is any chemical reaction occurring in the body. A metabolic pathway is a
series of small chemical reactions involved in the anabolism or catabolism of a substance.
Since a large amount of energy may be required or released in the formation of the substance, a
series of small steps, in which energy levels can be controlled, is more efficient than one single
reaction.