16
2 The Kinds of Ordinary Materials
freeze from the top down, leaving aquatic life to feed on the bottom. 8 If this rather
unusual property of life’s solvent did not hold, ice ages over the Earth would have
made life much more difficult.
Earth’s surface average temperature is currently 15 ◦ C above the freezing point of
water. 9 On planets at an average surface temperature below −33 ◦ C, liquid ammonia
(that is anhydrogenous NH 3 , not NH 4 OH) would serve as a good solvent, since the
ammonia molecule, like the water molecule, is strongly polar.
2.2 Mixtures, Solutions, Colloids, Sols, and Gels
Experiment is the sole judge of scientific ‘truth’.
— Richard Feynman
Mixtures of materials can have the properties of the three ordinary phases
of matter, solid, liquid, or gas, depending on the conditions. Some of these
mixtures are used by life systems. Homogeneous fluid mixtures with the mixed
particles comparable in size and density to the background fluid material are called
‘solutions’. Note that we use the term fluid to include both liquids and gases.
The mixed particles are the ‘solute’, and the background fluid the ‘solvent’. If
the interactions of a fluid with another material results in a solution, we say the
material has ‘dissolved’. If the mixture material in a fluid is also a fluid, we say that
the two fluids are ‘miscible’. If the size of the mixed particles is much less than
four thousand ångströms, a clear fluid will remain clear to visible light after the
particles are added and the fluid is stirred to make it homogeneous. A homogeneous
mixture containing a dispersion of particles much larger than the background fluid
particles but small enough to remain dispersed over times much larger than typical
observation times is called a ‘colloid’. Colloids may contain within the fluid a
dispersion of microstructures each with thousands to billions of atoms. The colloidal
particles typically make the colloid appear cloudy even if the background fluid was
clear. A mixture in a fluid with dispersed particles large enough to settle under the
influence of the Earth’s gravity is called a ‘suspension’ if settling is incomplete. In
this case, typically, the mixed particles are a few tens of thousands ångströms in size.
Mixtures with the mixed particles bigger than a few hundred thousand ångströms are
called heterogeneous or bulk mixtures.
8 However, under arctic and antarctic surface ice, ‘brinicles’ can form from concentrated and dense
brine dropping to the ocean floor, making structures looking like stalactites with frozen water at the
interface of the brine with the liquid ocean, even creating a layer of ice over the brine that spread
on the ocean floor, killing most of the covered life forms.
9 Without some greenhouse effect in our atmosphere, water would be in the solid phase over the
entire Earth.
2 The Kinds of Ordinary Materials
freeze from the top down, leaving aquatic life to feed on the bottom. 8 If this rather
unusual property of life’s solvent did not hold, ice ages over the Earth would have
made life much more difficult.
Earth’s surface average temperature is currently 15 ◦ C above the freezing point of
water. 9 On planets at an average surface temperature below −33 ◦ C, liquid ammonia
(that is anhydrogenous NH 3 , not NH 4 OH) would serve as a good solvent, since the
ammonia molecule, like the water molecule, is strongly polar.
2.2 Mixtures, Solutions, Colloids, Sols, and Gels
Experiment is the sole judge of scientific ‘truth’.
— Richard Feynman
Mixtures of materials can have the properties of the three ordinary phases
of matter, solid, liquid, or gas, depending on the conditions. Some of these
mixtures are used by life systems. Homogeneous fluid mixtures with the mixed
particles comparable in size and density to the background fluid material are called
‘solutions’. Note that we use the term fluid to include both liquids and gases.
The mixed particles are the ‘solute’, and the background fluid the ‘solvent’. If
the interactions of a fluid with another material results in a solution, we say the
material has ‘dissolved’. If the mixture material in a fluid is also a fluid, we say that
the two fluids are ‘miscible’. If the size of the mixed particles is much less than
four thousand ångströms, a clear fluid will remain clear to visible light after the
particles are added and the fluid is stirred to make it homogeneous. A homogeneous
mixture containing a dispersion of particles much larger than the background fluid
particles but small enough to remain dispersed over times much larger than typical
observation times is called a ‘colloid’. Colloids may contain within the fluid a
dispersion of microstructures each with thousands to billions of atoms. The colloidal
particles typically make the colloid appear cloudy even if the background fluid was
clear. A mixture in a fluid with dispersed particles large enough to settle under the
influence of the Earth’s gravity is called a ‘suspension’ if settling is incomplete. In
this case, typically, the mixed particles are a few tens of thousands ångströms in size.
Mixtures with the mixed particles bigger than a few hundred thousand ångströms are
called heterogeneous or bulk mixtures.
8 However, under arctic and antarctic surface ice, ‘brinicles’ can form from concentrated and dense
brine dropping to the ocean floor, making structures looking like stalactites with frozen water at the
interface of the brine with the liquid ocean, even creating a layer of ice over the brine that spread
on the ocean floor, killing most of the covered life forms.
9 Without some greenhouse effect in our atmosphere, water would be in the solid phase over the
entire Earth.