ACIDS, BASES AND SALTS notes Part 2
ACIDS,
BASES AND SALTS
On the basis of there chemical
properties, all the compounds can be classified into three groups.
- Acids,
- Bases, and
- Salts
Indicator for Testing Acids and
Bases
An indicator is a ‘dye’ that
changes color when it is put into an acid and base. An indicator
tells as whether the substance we are testing is an acid or a base by
change in its color.
The three common indicators to test for
acids and bases are: Litmus, Methyl orange and Phenolphthalein.
- Litmus: -- Litmus can be used in the form of litmus solution or in the form of litmus paper (Blue litmus and Red litmus). Litmus is natural indicator extracted from ‘lichen’ plant. The natural color of lichen is purple.
->An acid turns
blue litmus to red.
->A base (or
alkali) turns red litmus to blue.
- Methyl orange: -- Methyl orange is synthetic indicator. The natural color of methyl orange is orange.
->Methyl orange
indicator gives red color in acid solution.
->Methyl orange
indicator gives yellow color in basis solution.
- Phenolphthalein: -- Phenolphthalein is synthetic indicator. The natural color of phenolphthalein is colorless.
->Phenolphthalein
indicator is colorless in acid solution
->Phenolphthalein
indicator gives pink color in basic solution.
Turmeric is also a natural indicator.
It contains a yellow dye. It turns red in basic solution. The red
cabbage extract (obtain from red cabbage leaves) is also a natural
indicator. It is red in acidic solution but turns green on adding to
basis solutions.
Olfactory Indicators:
Those substances whose smell (or odour)
changes in acidic or basic solutions are called olfactory indicators.
Onion and vanilla extract are olfactory indicators.
- Onion has a characteristic smell. In basic solution the onion smell can not be detected. An acidic solution dose not destroys the smell of onions.
- Vanilla extract has a characteristic pleasant smell. In basis solution the pleasant smell cannot be detected. An acid solution dose not destroys the smell.
ACIDS
Acids are those substances which have a
sour taste. Acids change the color of blue litmus to red.
The acids present in plant materials
and animals are called organic acids. Examples are Acetic acid
(ethanoic acid), Citric acid, Lactic acid, Formic acid (methanoic
acid).
The acids prepared from the minerals of
the earth are called mineral acids. Examples are hydrochloric acid,
Sulphuric acid and Nitric acid.
Strong Acids and Weak Acids
All the acids are divided into two
groups: strong acids and weak acids.
(i)All the mineral acids are strong
acids. Hydrochloric acid, sulphuric acid and nitric acid are strong
acids.
(ii)The organic acids are weak acids.
Acetic acid, formic acid, tartaric acid and carbonic acid are weak
acids.
Concentrated and dilute acids
A concentrated acid is one which
contains the minimum possible amount of water in it. A dilute acid is
one which contains much more of water in it.
Diluting Acids
The dilution of concentrated acid
should always be done by adding concentrated acid to water gradually
with string and not by adding water to concentrated acid.
Properties of Acids
The important characteristic of acids
is:
- Acids have a sour taste
- Acids turns blue litmus to red
- Acids solutions conduct electricity
- Acids reacts with metals to form hydrogen gas
Metal + Acid
Salt + Hydrogen gas
Most of the acids
react with metals to form salts and evolve hydrogen gas. Hydrogen is
common to all acid.
Curd and sore food
stuffs should not be kept in metal vessels because curd and other
food stuffs contain acids which can reacts with metal of the vessel
to form poisonous metal compounds which can cause food poisoning.
- Acids reacts with metal carbonate (and metal hydrogen carbonates) to form carbon dioxide gas.
Metal carbonate +
Acid Salt + Carbon
dioxide + Water
- Acids react with bases (or alkali) to form salt and water.
Acid +Base
Salt + Water
The reaction
between an acid and base to form salt and water is called a
netralisation reaction.
- Acids react with metal oxides to form salt and water.
Metal oxide +
Acid Salt + Water
The acids also
react with metal hydroxides to form salt and water.
- Acids have corrosive nature.
The mineral acids
cause severe burns on the skin and attack and eat up materials like
cloth, wood, metal structures and stonework, so they are said to be
corrosive. Acids are never stored in metal container because they
gradually corrode and eat up metal container so they stored in glass
and ceramics container. The strong bases (or alkali) such sodium
hydroxide are also very corrosive, and attack and destroy our skin.
WHAT DO ALL ACIDS HAVE IN COMMON
An acid is a substance which
dissociates (or ionizes) on dissolving in water to produce hydrogen
ions [H+(aq)ions].
HCl(aq)
H+(aq) + Cl-(aq)
A common thong in all the acids is that
they produce hydrogen ions [H+(aq)ions] when dissolved in
water.
The aqueous solutions glucose and
alcohol do not show acidic character because hydrogen does not
separate out as hydrogen ions [H+(aq)ions] on dissolving in water.
The aqueous solution of acid conducts
electricity due to the presence of charge particles called ions in
it. Due to the absence of ions, glucose solution do not conducts
electricity. Distilled water dose not conducts electricity because it
dose not contain any ionic compound (like acids, bases of salts)
dissolved in it. Due to the presence of carbonic acid (which provides
ions to rain water), the rain water conducts electricity.
Acids Do Not Show Acidic
Behavior in the Absence of Water
In the absence of water, a substance
will not form hydrogen ions and will not show its acidic behavior.
Dry HCl gas dose not change the color of dry litmus paper because it
has no hydrogen ions [H+(aq)ions] in it. The HCl gas turns
‘wet’ blue litmus paper red because it dissolves in the water
present in wet litmus paper to form hydrogen ions, which can turns
blue litmus paper to red.
Strong Acids
An acid which is completely ionised in
water and produce s a large amount of hydrogen ions is called a
strong acid. Hydrochloric acid is completely ionized in water, so it
is a strong acid. Sulphuric acid and nitric acid is also strong
acids. Strong acids react very rapidly with other substance (such as
metals, metal carbonates and metal hydro carbonates).
Weak Acids
An acid which is partially ionized in
water and thus produces a small amount of hydrogen ions is called a
weak acid. Acetic acid (CH3COOH) is partially ionized in
water to produce only small amount of hydrogen ions, so it is weak
acid. Carbonic acid (H2CO3) and sulphurous acid
(H2SO3) are also weak acids.
When a concentrated solution of acid is
diluted by mixing water, then the concentration of hydrogen ions, H+
(aq) [or hydronium ions, H3O+ ] per unit
volume decreases.
BASES
Bases are those chemical substances
which have bitter taste. It changes the color of red litmus blue.
Bases are chemical opposite of acids. Base is a chemical substance
which can neutralize an acid.
Water Soluble Bases: Alkalis
Most bases do not dissolve in water but
some dissolve in water with out any chemical reaction. A base which
dissolves in water is called an alkali.
What do All the Bases have in
Common?
A common property of all the bases (or
alkali) is that they all produce hydroxide ions (OH- ions)
when dissolved in water. NaOH, KOH, Mg(OH)2, NH4OH
are all bases.
Strong Bases
A base which completely ionized in
water and thus produces a large amount of hydroxide ions (OH-
ions) is called a strong base (or a strong alkali). Sodium
Hydroxide (NaOH), potassium hydroxide (KOH) is strong bases.
Weak Bases
A base which is partially ionized in
water and thus produces a small amount of hydroxide ions (OH-
ions) is called a weak bases (or weak alkali). Ammonium
hydroxide (NH4OH), calcium hydroxide [Ca(OH)2]
are weak acids.
Properties of Bases
- Bases have bitter taste
- Bases feel soapy to touch
- Bases turn red litmus to blue
- Bases conduct electricity in solution(They are electrolytes)
- Bases react with some metals to form hydrogen gas
All the metal does
not react with bases to form salts and hydrogen gas.
- Bases react with acids to form salts and water.
When an acid and
base combine then real the neutralization reaction occurs due to
combination of hydrogen ions present in acid and hydroxide ions
presents in base to form water. neutrslisation
H+(aq)
+ OH-(aq)
H2O(l)
- Bases react with non metal oxide to form salt and water
Non-metal +
Base Salt + Water
STRENGH OF ACID AND BASE SOLUTIONS:
pH SCALE
Acidic solution has excess of hydrogen
ions but it also contains hydroxide ions.
Basic solution has excess of hydroxide
ions but it also contains hydrogen ions.
Both acidic solutions as well as basic
solution contain hydrogen ions. In 1909 Sorenson devised a scale
(Known as pH scale) on which acid solutions as well as basic
solutions could be represented by making use of the hydrogen ion
concentration in them.
The pH of a solution is inversely
proportional to the concentration of hydrogen ions in it.
The strength of an acid or base is
measured on a scale of numbers called the ph scale. The pH scale has
values from 0 to 14, pure number, no units.
According to pH scale: ---
- Neutral substances have a pH of exactly 7.
- Acids (or acidic solution) have a pH pf less than 7. Lower the pH, the stronger the acid.
- Bases (or basic solution) have a pH of more than 7. Higher the pH, the stronger the base (or alkali).
Universal Indicator
To obtain the idea of how acidic or
basic substance is, universal indicator is used.
Universal indicator is a mixture of
many different indicators (or dyes) which gives different color in
different pH values of the entire pH scale. Like litmus which can be
produced in the form of solution or paper.
Water will produce green color with
universal indicator.
Important of pH in everyday life
- pH in our digestive system
Dilute hydrochloric acid
helps in digesting our food. Excess acid in the stomach causes
indigestion. Being basic in nature, antacids react with excess in
stomach and neutralise it. Magnesium hydroxide (milk of magnesia) and
sodium hydrogen carbonate (baking soda) are used as antacids.
- ph change as the cause of tooth decay
The bacteria
present in our mouth breaks down the sugar to form acids. Tooth decay
starts when the pH of acid formed in the mouth falls 5.5. The best
way to prevent tooth decay is to clean the mouth thoroughly after
eating food.
- Prints and Animals are Sensitive to pH Changes
- Soil pH and Plant Growth. Most of the plants grow best when pH of the soil is close to 7. If the soil is too acidic or too basic, the plant grows too badly or do not grow at all. If the soil is too acidic, then it is treated with materials like quicklime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate).
- pH Change and Survival of Animals. Our body works well within a narrow range of 7.0 to 7.8. If this pH range gets disturbed in the body, then many ailments can occur.
- self defense by Animals Plants by through Chemical Warfare
An ant’s string
injects methanoic acid into the skin of a person causing burning
pain. When a person happens of a nettle plant accidentally, the
stinging hair leaves injects methanoic acid into the skin of the
person causing burning pain.
SALTS
A salt is a
compound formed from an acid by the replacement of hydrogen in the
acid by a metal. Salts are formed when acids reacts with bases. Just
like acids and bases, solutions of salts in water conduct
electricity. Salts are ionic compounds.
Family of salts
The salts having
the same positive ions (or same negative ions) are said to belong to
the family of salts. For example sodium chloride (NaCl) and sodium
sulphate (Na2SO4) belong to the same family of
salts called ‘sodium salts’.
The pH of Salt
Solutions
Though the aqueous
solutions of many salts are neutral (having a ph of 7), some salts
produce acidic or basic solutions when dissolve in water
The acidic nature
and basic nature of some salt solutions can be explained on the basis
of hydrolysis of salts.
- The salts of strong acid and strong bases give neutral solutions
- The salts of strong acid ands and weak bases give acidic solution
- The salts of weak acids and strong bases give basis basic solutions
COMMON SALT
(SODIUM CHLORIDE)
The chemical name
of common salt is sodium chloride (NaCl).
Sodium chloride
can be prepared by the combination of sodium hydroxide and
hydrochloric acid:
NaOH(aq) +
HCl(l) NaCl(aq) +
H2O(l)
How Common Salt is
obtained
- Common Salt from Sea-water – Common salt obtains from sea-water by the process of evaporation.
- Common Salt from Underground Deposits – Rock is mined from the underground deposits just like coal.
Uses of Common Salt
- Common salt is used as a raw material for making chemicals like: sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, hydrochloric acid , hydrogen chlorine, and sodium metal.
- Common salt is used in cooking food.
- Common salt is used as a preservative.
- Common salt is used in the manufacturing of soap.
- Common salt used to melt ice which collects in the roads during winter in cold countries.
Chemicals from
Common Salt
SODIUM HYDROXIDE
Sodium hydroxide
is commonly known as caustic soda.
When electricity
is passed through a concentrated solution of sodium chloride, it
decomposes to form sodium hydroxide, chlorine and hydrogen.
2NaCl (aq) +
2H2O(l)
2NaOH(aq) + Cl2(g) H2(g)
Chlorine gas is
produced at the anode and hydrogen gas is produced at the cathode.
Sodium hydroxide solution formed near the cathode. The process of
sodium chloride solution is called chlor-alkali process. The three
very useful products obtained by the electrolysis of sodium chloride
solution called brine (or chlor-alkali process) are sodium hydroxide,
chlorine and hydrogen.
Uses of Sodium
Hydroxide
- Sodium hydroxide is used for making soaps and detergents
- Sodium hydroxide is used for making artificial textile fibers
- Sodium hydroxide is used in the manufacturing of paper
- Sodium hydroxide is used in purifying bauxite ore from aluminum metal is extracted
- Sodium hydroxide is used de-greasing metals, oil refining, and making dyes and bleaches
Uses of Chlorine
- Chlorine is to used to sterilize drinking water
- Chlorine is used in the production of bleaching powder
- Chlorine is used in the production of hydrochloric acid
- Chlorine is used to make plastics
- Chlorine is used for making solvents for dry-cleaning
Uses of Hydrogen
- Hydrogen is used in the hydrogenation of oils to obtain solid fats
- Hydrogen is used in the production of hydrochloric acid
- Hydrogen is used to make ammonia for fertilizers
- Hydrogen is used to make methanol
- hydrogen is used as a fuel for rockets
Uses of Hydrochloric acid
- Hydrochloric acid is used for cleaning iron sheets before tin-plastic or galvanization
- Hydrochloric acid is used in the preparation of chlorides such as ammonium chloride
- Hydrochloric acid is used in medicines and cosmetics
- Hydrochloric acid is used is textile, dyeing and tanning industry
- Hydrochloric acid is used in making plastics
WASHING SODA
Washing soda is sodium carbonate
containing 10 molecules of water of crystallization.
Washing is produced from sodium
chloride in following three steps
- A cold and concentrated solution of sodium chloride is reacted with ammonia and carbon dioxide to obtain sodium hydrogen carbonate.
NaCl +
NH3 + H2O CO2
NaHCO3 + NH4Cl
- On heating sodium hydrogen carbonate decomposes to form sodium carbonate
2NaHCO3
Na2CO3
+ CO2 + H2O
- Anhydrous sodium carbonate is dissolved in water and recrystallised to get washing soda crystals containing 10 molecules of water of crystal satin.
Na2CO3
+ 10H2O
Na2CO3.10H2O
Properties of washing soda
- Washing soda is a transparent crystalline solid
- Washing soda is one of the metal carbonates which are soluble in water
- The solution of washing soda in water is alkaline which turns red litmus to blue
- Detergent properties (or cleansing properties)
Use of sodium
carbonate
- Sodium carbonate is used as a “cleansing agent” for domestic proposes.
- Sodium carbonate is used for removing permanent hardness of water.
- Sodium carbonate is used in the manufacturing of glass, soap and paper.
- Sodium carbonate is used in the manufacturing of sodium compounds such as borax.
BAKING SODA
The chemical name of backing
soda is sodium hydrogen carbonate and the formula is NaHCO3.
Production of sodium hydrogen carbonate
Sodium carbonate is
produced by reacting a cold and concentrated solution of sodium
chloride with ammonia and carbon dioxide
NaCl + NH3
+ H2O + CO2
NaHCO3 + NH4Cl
Properties of sodium hydrogen carbonate
- Sodium hydrogen carbonate consists of white crystals which are sparingly soluble in water.
- Sodium hydrogen carbonate is a mild, non-corrosive base and water is mildly alkaline.
- When solid hydrogen carbonate is heated, then it decomposes to give sodium carbonate and carbon dioxide.
Heat
2NaHCO3
----------- > Na2CO3 +
CO2 + H2O
Uses of sodium hydrogen carbonate
- Sodium hydrogen carbonate is used as an antacid in medicine to remove acidity of the stomach.
- Sodium hydrogen carbonate is used in making baking power
- Sodium hydrogen carbonate is used in fire extinguishers.
BLEACHING POWER
Bleaching power is calcium oxychloride
and the formula is CaOCl2.
Preparation of bleaching power
Bleaching power is prepared by passing
chlorine gas over dry slaked lime.
Ca(OH)2 + Cl2
CaOCL2
+ H2O
Properties of bleaching power
- Bleaching power is a white power which gives a strong smell of chlorine.
- Bleaching power is soluble in cold water.
- Bleaching power reacts with dilute acids to produce chlorine.
CaOCl2
+ H2SO4
CaSO4 + Cl2 + H2O
Uses of Bleaching Power
- Bleaching power is used for bleaching cotton and linen in textile industry
- Bleaching is used for disinfectant drinking water.
- Bleaching power is used for the manufacturing of chloroform (CHCl3).
- Bleaching power is used for making wood unshrinkable.
- Bleaching power is used as an oxidizing agent in many chemical industry.
PLASTER OF PARIS
Plaster of Paris is calcium sulphate
hemi hydrate (calcium carbonate half-carbonate) and the formula is
CaSo4.1/2H2O.
Preparation of Plaster of Paris
Plaster of Paris is prepared by heating
gypsum (CaSO4.2H2O calcium sulphate dihydrate) to a temperature of
100o C.
CaSO4.2H2O
CaSO4.1/2H2O + 1.1/2H2O
Properties of Plaster of Paris
- Plaster of Paris is a white power.
- Plaster of Paris has a very remarkable property of setting into a hard mass on wetting in water.
- Plaster of Paris should be stored in a moister proof container.
Uses of plaster of Paris
- Plaster of Paris is used in hospitals for setting fractured bones in the right position.
- Plaster of Paris is used in making toys, decorative materials, cheap ornaments, black-board chalks and cast for statues.
- Plaster of Paris is used as a fire-proofing material.
- Plaster of Paris is used in chemical laboratories for sealing air-gaps in apparatus.
- Plaster of Paris is used for making surfaces smooth before painting them.
WATER OF CRYSTALISATION
The water molecules which form part of
the structure of a crystal (of a salt) are water of crystallization.
The salt contain water of a crystallization are called hydrated salt.
Every hydrated salt has a “fixed
number” of molecule of water of crystallization in its one formula
unit. For example copper sulphate crystal contain 5 molecules of
water of crystallization per formula unit and hence written as
CuSO4.5H2O.
Water of crystallization is a part of
‘crystal structure’ of a salt. Since water of crystallisation is
not free water, it does not wet the salt.
The water of crystallization gives the
crystals of the salts their ‘shape’ and, in some cases, imparts
them ‘color’.
ACTION OF HEAT ON HYDRATED SALTS
When hydrated salts are heated
strongly, they lose their water of crystallization. The salts which
have lost their water of crystallization are called anhydrous salts.
QUESTION FOR PRACTICE
- Which gas is usually liberated when an acid reacts with a metal?
- While diluting an acid, why is it recommended that the acid should be added to water and not water to acid?
- What happens when an acid reacts with a metal carbonate?
- What happens when an acid reacts with a metal hydrogen carbonate?
- What happens when an acid reacts with a base? Give equation of the reaction involved. What is the special name of this reaction?
- What happens when an acid reacts with a metal oxide? Write the equation of the reaction involved.
- What happens when carbon dioxide gas passed through lime water: (a) for a short time, and (b) for a considerable time? Write equations of the reactions involved.
- Complete and balance the following chemical reactions:
(a) Zn(s) +
HCl(aq)
(b) Na2CO3(s)
+ HCl(aq)
(c) NaHCO3(s)
+ HCl(aq)
(d) NaOH(aq) +
HCl(aq)
(e) CuO(s) +
HCl(aq)
- What are organic acids and mineral acids? Give examples of each.
- Which element is common to all acids?
- Why do HCl, H2SO4, HNO3 etc... show acidic character in aqueous solution while solutions of compounds like glucose and alcohol do not show acidic character?
- Why does dry HCl gas not change the color of the dry litmus paper?
- Why does distilled water not conduct electricity whereas rain water does?
- Give the name and formulae of two strong acids and two weak acids.
- Fill in the following statement with a suitable word:
Substances do not
show their acidic properties without……..
- What does pH of a solution signify? Three solutions A, B, and C have pH value of 6, 4 and 10 respectively. Which of the solution is highly acidic?
- Two solutions X and Y have pH=4 and pH=8, respectively. Which solution will give alkaline reaction and which one acidic.
- The pH of a cold drink is 5. What will be its action an blue and red litmus solution?
- A solution turns red litmus blue, its pH is like to be:
(a) 1 (b) 4 (c) 5
(d) 10
- (a) Which is more acidic, pH = 2 or pH = 11?
(b) Which is more
basic pH = 8 or pH = 11?
- Fresh milk has a pH of 6. How do you think the pH would change a it turns into curd? Explain your answer.
- What effect does the concentration of H+(aq) ions have on the nature of the solution?
- Name the indicator which can give us an idea of how strong or weak an acid or base is?
- How does a universal indicator work?
- Two solutions X and Y are tasted with universal indicator. Solution X turns orange where as solution Y turns red. Which of the solution is a stronger acid?
- Under what soil conditions do you think a farmer would treat the soil of his fields with quicklime or slaked lime or chalk?
- How does an antacid work? Name two antacid.
- Explain the pH change as the tooth decay. How can tooth decay caused by pH change be prevented?
- What happens during a bee sting? What is its remedy?
- The pH of a soil A is 7.5 while that of soil B is 4.5. Which of the two soils, A or B, should be treated with powered chalk to adjust its to adjust its pH and why?
- A salt X when dissolved in distilled water gives a clear solution which turns red litmus blue. Explain the phenomenon.
- Explain why, an aqueous solution of sodium chloride is neutral but an aqueous solution of sodium carbonate is basic.
- What is a salt? Give the names and formulae of any two salts. Also name the acids and bases from which these salts may be obtained.
- What is meant by a family of salts? Explain with examples.
- Write the chemical name and formula of common salt.
- Name the major salt present in sea-water?
- Name three chemicals made from common salt.
- Give any two uses of common salt.
- Name the salt which is used as a preservative in pickle, and in curing meat and fish.
- What happens when a concentrated solution of sodium chloride is electrolyzed? Write the equation of the reaction involved.
- The electrolysis of an aqueous solution of sodium chloride gives us three products. Name them.
- Explain why, chlorine is used for sterilizing drinking water supply.
- Name the product formed when Cl2 and H2 produced during the electrolysis of brine are made to combine.
- Write the chemical formula of sodium carbonate.
- Name a metal compound which has detergent properties.
- Name a sodium compound used for softening hard water.
- What is the common name Na2CO3.10H2O?
- Name the metal whose carbonate is known as washing soda.
- What is the chemical name of baking soda?
- What is the chemical formula of baking soda?
- What is the common name of sodium hydrogen carbonate?
- Name an acid which is present in baking powers.
- What happens when a solution of sodium hydrogen carbonate is heated? Write equation of the reaction involved.
- Give the chemical formula of washing soda and baking soda.
- What is the chemical name of bleaching power?
- What is the chemical formula of bleaching power?
- What are the materials used for the preparation of bleaching power?
- Name the substances obtained by the action of chlorine on solid slaked lime.
- Name one compound of calcium which is used for bleaching cloth.
- Which is the real bleaching agent present in bleaching power?
- What is plaster of Paris? Write the chemical composition of plaster of Paris.
- Name the raw material used for the preparation of plaster of Paris.
- What is the commercial name of calcium sulphate hemi-hydrate?
- What will happen if heating is not controlled while preparing plaster of Paris?
- State two important uses of plaster of Paris.
- What is meant by ‘water of crystallization’
- What is meant by ‘hydrated’ and ‘anhydrous’ salts? Explain with an example.
- What happens when a copper sulphate crystal are heated strongly/ explain with the help of an equation.
- Write the names, formula and colors of any two hydrated salts.
- What happens when copper sulphate crystals are added to anhydrous copper sulphate? Explain with the help of an equation.
Chemistry for class 10....
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carbon-and-its-compound-notes
periodic-classification-of-elements
unsaturated-hydrocarbon
metal-and-non-metals-notes
chemical-reaction-and-equations-notes-2
periodic-classification-of-elements
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