# 18.5 Occurrence, preparation, and compounds of hydrogen  (Page 6/9)

 Page 6 / 9

Hydrofluoric acid is unique in its reactions with sand (silicon dioxide) and with glass, which is a mixture of silicates:

${\text{SiO}}_{2}\left(s\right)+\text{4HF}\left(aq\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{SiF}}_{4}\left(g\right)+{\text{2H}}_{2}\text{O}\left(l\right)$
${\text{CaSiO}}_{3}\left(s\right)+\text{6HF}\left(aq\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{CaF}}_{2}\left(s\right)+{\text{SiF}}_{4}\left(g\right)+{\text{3H}}_{2}\text{O}\left(l\right)$

The volatile silicon tetrafluoride escapes from these reactions. Because hydrogen fluoride attacks glass, it can frost or etch glass and is used to etch markings on thermometers, burets, and other glassware.

The largest use for hydrogen fluoride is in production of hydrochlorofluorocarbons for refrigerants, in plastics, and in propellants. The second largest use is in the manufacture of cryolite, Na 3 AlF 6 , which is important in the production of aluminum. The acid is also important in the production of other inorganic fluorides (such as BF 3 ), which serve as catalysts in the industrial synthesis of certain organic compounds.

Hydrochloric acid is relatively inexpensive. It is an important and versatile acid in industry and is important for the manufacture of metal chlorides, dyes, glue, glucose, and various other chemicals. A considerable amount is also important for the activation of oil wells and as pickle liquor—an acid used to remove oxide coating from iron or steel that is to be galvanized, tinned, or enameled. The amounts of hydrobromic acid and hydroiodic acid used commercially are insignificant by comparison.

## Key concepts and summary

Hydrogen is the most abundant element in the universe and its chemistry is truly unique. Although it has some chemical reactivity that is similar to that of the alkali metals, hydrogen has many of the same chemical properties of a nonmetal with a relatively low electronegativity. It forms ionic hydrides with active metals, covalent compounds in which it has an oxidation state of 1− with less electronegative elements, and covalent compounds in which it has an oxidation state of 1+ with more electronegative nonmetals. It reacts explosively with oxygen, fluorine, and chlorine, less readily with bromine, and much less readily with iodine, sulfur, and nitrogen. Hydrogen reduces the oxides of metals with lower reduction potentials than chromium to form the metal and water. The hydrogen halides are all acidic when dissolved in water.

## Chemistry end of chapter exercises

Why does hydrogen not exhibit an oxidation state of 1− when bonded to nonmetals?

The electronegativity of the nonmetals is greater than that of hydrogen. Thus, the negative charge is better represented on the nonmetal, which has the greater tendency to attract electrons in the bond to itself.

The reaction of calcium hydride, CaH 2 , with water can be characterized as a Lewis acid-base reaction:
${\text{CaH}}_{2}\left(s\right)+{\text{2H}}_{2}\text{O}\left(l\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}\text{Ca}{\left(\text{OH}\right)}_{2}\left(aq\right)+{\text{2H}}_{2}\left(g\right)$

Identify the Lewis acid and the Lewis base among the reactants. The reaction is also an oxidation-reduction reaction. Identify the oxidizing agent, the reducing agent, and the changes in oxidation number that occur in the reaction.

In drawing Lewis structures, we learn that a hydrogen atom forms only one bond in a covalent compound. Why?

Hydrogen has only one orbital with which to bond to other atoms. Consequently, only one two-electron bond can form.

What mass of CaH 2 is necessary to react with water to provide enough hydrogen gas to fill a balloon at 20 °C and 0.8 atm pressure with a volume of 4.5 L? The balanced equation is:
${\text{CaH}}_{2}\left(s\right)+{\text{2H}}_{2}\text{O}\left(l\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}\text{Ca}{\left(\text{OH}\right)}_{2}\left(aq\right)+{\text{2H}}_{2}\left(g\right)$

What mass of hydrogen gas results from the reaction of 8.5 g of KH with water?
$\text{KH}+{\text{H}}_{2}\text{O}\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}\text{KOH}+{\text{H}}_{2}$

0.43 g H 2

What are molecules
a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction
Danny
True
David
exactly
Harriet
true
lucy
were is ruth
Danny
Perfect
BISWAJIT
what is partial pressure law
what is the structural formular for 2,3-dimethylbutane?
name the following compound (COOH)2
Mercy
CH3-CH(CH3)-CH(CH3)-CH3 this is 2,3-dimethylbutane
galina
(COOH)2 is oxalic acid
thiru
what is chemistry
chemistry is the study of chemical reactions
lucy
Chemistry is the study of matter, its properties, how and why substances combine or separate to form other substances, and how substances interact with energy.
Danny
chemistry is the study of matter, it's properties and composition
alexandra
hello Lucy
alexandra
hello boris nice to meet u all
alexandra
hello
lucy
lucy were you from and what grade are you doing
Danny
am from Abuja and am in ss1
lucy
ss1 some one translate that for me we use grades in my country
Danny
lucy
okay am a chemistry and biology teacher from Zambia
Danny
should be grade 10 I think
alexandra
oh okay hello
lucy
thats good Mr mwanza
Harriet
Danny
GCE 12
Harriet
from where
Danny
lusaka
Harriet
text me on whats up
Danny
we help each other
Danny
yes sir
lucy
me ss2
Richard
so are a final year student
kabu
wow I didn't know it chat group
Emmanuel
hello..
Edgar
hello
edet
hi
Hey
Faith
I'm new here
edet
What is the chemical formula for alcohol? is the chemical formula for alcohol?
CH3CH2OH
Anupam
20 element are what element?
What is Chemistry?
thiru
Esther
studying about the rate of chemical is ?
thiru
Chemistry is the branch of sciences dealing with the composition of substances and their properties and reaction.
Jeremiah
chemical reaction is the process in which one or more chemical substances react with other chemical substance and converted one or more different substances.
Aisha
what is isotopy
Isotopy is one of two or more atoms having the same atomic numbers but different mass number.
Esther
Molar mass of Chlorine
what is chemistry
Molar mass of Chlorine atom
Sakyi
chem is the study of structure, properties of matter and changes that matter undergo
Sheila
m.m of Cl is 35.5
Sheila
what is an acid
example, HCl, H2SO4, HNO3
galina
an acid is a substance that dissolves in water to give hydrogen oins as the only negatively charged ions
Sheila
Galina is correct those are some examples of acids , others are ethanedioic acid, ethanoic acid , methanoic acid ma ans above is tha definition of an acid
Sheila
An acid is a substance with particular chemical properties including litmus red, neutralizing alkalis and dissolving some metals.
Esther
Shelia is also right 💯💯
Esther
what is hydrocarbon?
Edgar
is a group of carbon atoms that is bonded with an alkyl group eg methyl butane
Sheila
A hydrocarbon is a compound that contains only hydrogen and carbon atoms
martha
it means only carbon and hydrogen atoms are bonded..
Edgar
when ammonia and hydrogen ion bond together to form ammonium ion the bond formed is called
coordinate bond
Sheila
its called Dative covalent bond\ coordinate bond..
Favour
what are the factors affecting chemical equilibrium
Zee
what IS the meaning of esterification
it is converting a compound by replacing the hydrogen of an acid by an alkyl other organic group maybe caboxyl
Sheila
It is the method in which esters are produced. When alcohols are treated with carboxylic acids in presence of an acid,sweet smelling esters are produced.
BISWAJIT
thermodynamic first law
The first law of thermodynamics, also known as Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another
Alysa
what is any isotope
An isotope is atoms of a single element(same atomic number) that differ in the number of neutrons in their nuclei (different masses)
Salman
what is the difference between covalent bonding and ionic bonding
Wesley
A covalent bond is where sharing of electrons is between atoms or two non metals e.g chlorine and another chlorine atom whereas an ionic bond is formed between a metal and a non-metal such as magnesium metal and chlorine non-metal giving us MgCl2
Sheila
am new here someone should help me with balance equation ,I don't know how to balance equation
Joy