acids, alkalis and indicators prepared by mdm ry leow the chinese high school
TRANSCRIPT
Acids, Alkalis and Indicators
Prepared by Mdm RY LeowThe Chinese High School
AcidsAcids
• What causes the sour taste in these beverages?
The presence of citric acid.
Some Common Acids
• Organic acids are found in living things. • Which of the acids listed above are organic acids? • Hydrochloric acid is an mineral acid (inorganic acid) and is commonly
found in science laboratories.
Acids 1 All solutions of acids contain hydrogen
ions,H+
2 Examples of acids commonly found in the laboratories.
• Hydrochloric acid (HCl)
• Sulphuric acid (H2SO4)
• Nitric acid (HNO3)
• Ethanoic acid (CH3COOH)
Physical properties of acidic solutions
Concentrated acids are corrosive.
Note: All acids only show acidic properties in the presence of water!
Physical properties of acidic solutions1. Acids taste sour.
2. Acids turn blue litmus paper red but
have no
effect on red litmus paper.3. They have pH less than 7.
4. They are good electrical conductors.
*All acids can only show their acidic
properties in the presence of water.
Chemical properties of acids1.Dilute acids react with some metals (K, Na,
Ca, Mg, Zn, Fe) to produce hydrogen gas.metal + acid salt + hydrogen
*Dilute acids do not react with copper, silver, gold
eg Mg + 2HCl MgCl2 + H2
Mg + H2SO4 MgSO4 + H2
Chemical properties of acids2. An acid reacts with a carbonate to produce
2HCl + CaCO3 CO2 + CaCl2 + H2O
Carbon dioxide gasis bubbled into
limewater
White precipitate is formed
acid + carbonate carbon dioxide gas + salt + water
a salt, water and carbon dioxide.
Chemical properties of acids
3. An acid reacts with a base toform a salt and water
only.
The reaction between an acid and a base to form a salt and water only is called neutralisation
acid + base salt + water
HCl + NaOH NaCl + H2O
HNO3 + KOH KNO3 + H2O
H2SO4 + Ca(OH)2 CaSO4 + 2H2O
H2SO4 + CuO CuSO4 + H2O
Some Uses of Acids
Hydrochloric acid
Sulphuric acid
Nitric acid
Ethanoic acid
Citric acid
Cleaning metallic surfaces before they are painted or coated with other metals
Used as an electrolyte in car batteries making fertilisers, and plastics
Making fertilisers and explosives
Preserving food and cooking
Making health salts
Alkalis• Many household products such as
toothpaste, soap and detergents contain alkalis.
Click the picturefor uses
of alkalis.
Alkalis
1 All solutions of alkalis contain hydroxide ions, OH -
2 Examples of common alkalis found in the laboratories are
Sodium hydroxide solution NaOH
Potassium hydroxide solution KOH
Calcium hydroxide solution Ca(OH)2
Ammonia solution NH3.H2O
Physical Properties of Alkaline solutions
• Strong alkalis are corrosive
liquids.
*All alkalis can only show their alkaline properties
in the presence of water.
Physical Properties of alkaline solution
1. Alkalis taste bitter.
2. They feel soapy.
3. They turn red litmus paper blue but have no effect on blue litmus paper.
4. Alkalis are good electrical conductors.
5. They have pH greater than 7.
NaCl + H2O + NH3
Chemical Properties of Alkalis
1. An alkali reacts with an ammonium salt to produce
2. An alkali neutralises an acid to form a salt and water. alkali + acid salt + water
ammonia gas, salt and water.alkali + ammonium salt salt + water + ammonia gas
KCl + H2O
e.g. NaOH + NH4Cl
e.g. KOH + HCl
AlkalisAlkalis Common names Uses
Sodium hydroxide caustic soda Making soap, washing powder, drain cleaner
Potassium hydroxide caustic potash Making dyes for fabric and paint removers
Calcium hydroxide slaked lime Reducing acidity of soil and making mortar
Aqueous ammonia Making fertilisers and (Ammonia solution) household cleaning liquids
Indicators• Indicators are dyes which change colour with
the acidity or alkalinity of a solution.
• Some common indicators are (litmus, methyl orange, phenolphthalein, universal indicator)
pH scale
The pH scale is a range of numbers from 0 to 14, which indicates how acidic or alkaline a substance is.
pH scale
Other indicator such as pH paper can be used
A pH meter is an electronic device that can be use to measure the acidity or the alkalinity of solutions very effectively.
(a) pH meter being used to measure the pH of water in swimming pool
(b) pH meter is used to measure pH of the soil
Neutralisation
1 Neutralisation occurs when an acid neutralises a base or an alkali to form salt and water.(An indicator can be use to find the pH 7 of the solution)
*acid + base salt + water H2SO4 + MgO MgSO4 + H2O
*acid + alkali salt + water HNO3 + KOH KNO3 + H2O
•Acid and alkali are reactants.•salt and water are products.
Neutralisation
2 Example of everyday uses of neutralisation
• Shampoo (a mild alkali) and conditioner (a mild acid)
• Toothpaste (alkaline) neutralises acids produced by bacteria
• wasp sting (alkaline) is treated with vinegar to
relieve pain
• Excess acid in the soil is neutralised by adding
slaked lime (calcium hydroxide)
Salts• Salts are metal compounds that can be made
from acids.* All acids contain hydrogen.
*When the hydrogen in an acid is replaced by a metal, we get a salt.
nitric acid
hydrochloric acid
sulphuric acid
nitrates
chlorides
sulphates
Preparation of Salts
1 The four methods of preparing salts are:(a) precipitation of an insoluble salt (mixing)
HCl + AgNO3 AgCl + HNO3
(b) neutralisation of an acid with a base (excess insoluble oxide or hydroxide) CuO + H2SO4 CuSO4 + H2O
(c) neutralisation of an acid with an alkali (soluble hydroxide)
HCl + KOH KCl + H2O
(d) reaction of an acid with excess insoluble carbonate
CuCO3 + 2HCl CuCl2 + H2O + CO2
Flowchart to decide which method to use
Start
Is the salt soluble?(a) PRECIPITATION METHOD
Mix solutions of two soluble salts to precipitate an insoluble salt.eg NaCl + AgNO3 AgCl + NaNO3
React (b) acid with metal oxide
or (c) acid with alkalior(d) acid with metal carbonate
Are all reactants soluble in water?
(c) Mix acid with alkali to produce salt and watereg HCl + NaOH NaCl + H2O
(b)Mix acid and excess metal oxideor (d) excess metal carbonate to produce salt?
eg CuO + H2SO4 CuSO4 + H2OMgCO3 + H2SO4 MgSO4 +H2O+CO2
No
Yes
No
Yes
SaltsSoluble Insoluble
All sodium, potassium and
ammonium salts
All nitrates
All chlorides except lead(II) chloride and silver chloride.
All sulphates except lead(II) sulphate, barium sulphate and
calcium sulphate
sodium carbonate, All other carbonates
potassium carbonate
and ammonium carbonate