ion of hydrochloric acid. What
was the strength of the acid solution?

2. After neutralizing a solution of sodium hydroxide with nitric acid,
there remained after evaporation 100 g. of sodium nitrate. How much of
each substance had been used?

3. A solution contains 18 g. of hydrochloric acid per 100 cc. It
required 25 cc. of this solution to neutralize 30 cc. of a solution of
sodium hydroxide. What was the strength of the sodium hydroxide solution
in parts per hundred?

4. When perfectly dry sulphuric acid is treated with perfectly dry
sodium hydroxide, no chemical change takes place. Explain.

5. When cold, concentrated sulphuric acid is added to zinc, no change
takes place. Recall the action of dilute sulphuric acid on the same
metal. How do you account for the difference?

6. A solution of hydrochloric acid in benzene does not conduct the
electric current. When this solution is treated with zinc, will hydrogen
be evolved? Explain.

7. (a) Write equation for preparation of hydrogen from zinc and dilute
sulphuric acid. (b) Rewrite the same equation from the standpoint of
the theory of electrolytic dissociation, (c) Subtract the common
SO_{4} ion from both members of the equation, (d) From the resulting
equation, explain in what the preparation of hydrogen consists when
examined from the standpoint of this theory.

8. In the same manner as in the preceding exercise, explain in what the
action of sodium on water to give hydrogen consists.

CHAPTER XI

VALENCE

~Definition of valence.~ A study of the formulas of various binary
compounds shows that the elements differ between themselves in the
number of atoms of other elements which they are able to hold in
combination. This is illustrated in the formulas

HCl, H_{2}O, H_{3}N, H_{4}C.
(hydrochloric acid) (water) (ammonia) (marsh gas)

It will be noticed that while one atom of chlorine combines with one
atom of hydrogen, an atom of oxygen combines with two, an atom of
nitrogen with three, one of carbon with four. The number which expresses
this combining ratio between atoms is a definite property of each
element and is called its _valence_.

DEFINITION: _The valence of an element is that property which determines
the number of the atoms of another element which its atom can hold in
combination._

~Valence a numerical property.~ Valence is therefore merely a numerical
relation and does not convey any information in regar