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Chemistry SS1 Term 3

Chemistry SS1 Term 3

SCHEME OF WORK FOR THIRD TERM SS1 E-NOTE

• Acids, Bases and Salts: Acids
• Acids Bases and Salts: Bases
• Acids, Bases and Salts: Salts
• Water
• Carbon and its Compounds: Allotropes of Carbon
• Carbon and its Compounds: Coal
• Carbon and its Compounds: CO, CO2 and Trioxocarbonates
• Carbon and its Compounds: Trioxocarbonates (IV)
• Hydrocarbons and Crude Oil
• Volumetric (Quantitative) Analysis
• SS1 Chemistry Third Term Examination

 

ACIDS

CONTENT

1. Definition of Acid
2. Strength of an Acid
3. Basicity of an Acid
4. Characteristics of Acid (Physical Properties)
5. Preparation of Acids
6. Reaction of Acids (Chemical Properties)
7. Uses of Acids

 

Definition of Acid

Acids are associated with the sour taste we feel when we take fruits such as lemon, lime and oranges especially when they are not ripe. Palm wine left open in the air becomes sour because of the formation of an acid.

An acid is a substance which produces hydrogen ions (or protons) as the only positive ion when dissolved in water. For example, hydrochloric acid (HCl) dissolves in water to form hydrogen ion (H⁺) and hydroxyl ion (OH^–). This process is known as ionization. There are two main classes of acids: Organic acids and mineral or inorganic acids. The former occur as natural products in plants or animal materials while the later can be prepared from mineral elements or inorganic matter. Acids can also be grouped into Strong acids (ionizes completely) and Weak acids (ionizes partially).

Some Organic and Inorganic Acids

	Organic acids	Source		Inorganic acids	Constituents
	Ethanoic acids	Vinegar		Hydrochloric acid	Hydrogen, Chlorine
	Citric acids	Lime, Lemon		Tetraoxosulphate (vi) acid	Hydrogen ,Chlorine, Sulphur, Oxygen
	Fatty acids	Fats and Oil		Trioxonitrate (v) acid	Hydrogen, Nitrogen, Oxygen

Strength of an Acid

Strength of an acid is defined as the degree or the extent to which an acid ionizes in water. Based on this fact, acids can be weak or strong.

Strong acids are those that ionize completely in water. Examples of strong acids are H₂SO₄, HCl, HNO₃, HBr, HI etc. For example HCl ionizes completely according to the equation below:

HCl → H⁺  + Cl^–  (100% ionization)

Strong acids are also strong electrolytes i.e. they have high electrical conductivity.

Weak acids are those that ionize partially in water. Examples are organic acids, such as (Ethanoic acids, Citric acids, amino acids)  and  some inorganic acids such as HNO₂,H₂CO₃,H₃PO₄,HF etc. For example ethanoic acid, CH₃COOH, ionizes partially in water according to the equation below:

CH₃COOH ⇋ CH₃COO^–  +  H⁺

Weak acids are also weak electrolyte because they are poor conductor of electricity.

Basicity of an Acid

All acids in an aqueous solution yield hydrogen ions which can be replaced by metallic ion.

Chemistry SS1 Term 3

The basicity of an acid is the number of replaceable hydrogen ions, H⁺, in one molecule of the acid.

	Acids	Basicity
	HCl	1
	H2SO4	2
	H3PO4	3
	H2CO3	2
	CH3COOH	1

Characteristics of Acids (Physical Properties)

1. Acids turn blue litmus paper red.
2. They have sour taste; e.g. sour taste of unripe fruits.
3. Strong acids are corrosive in concentrated form; e.g. HCl, H₂SO₄

EVALUATION

1. Define an acid and give two examples each of organic acid and inorganic acid
2. Differentiate between a strong acid and a weak acid. Give two examples of each.
3. (a) What is basicity of an acid? (b). Mention four physical properties of an acid.
4. Compare and contrast the electrical conductivity of HCl and CH₃COOH

 

Preparation of Acids

1. Dissolving non-metallic oxide (acid anhydride) in water.

Carbon (iv) oxide dissolves in water to form weak acid, trioxocarbonate (iv) acid.

CO_2(g) +  H₂O_(l)   →    H₂CO_3(aq)

 

2. Direct combination of constituent elements.

Hydrogen reacts directly with Halogens in the presence of catalyst to form halogen acids gas which dissolves readily in water to form acid.

			activated charcoal
H2(g)	+	Cl2(g)	→	2HCl(g)
			heat

3. Heating Hydrogen gas and bromine vapour, in the presence of platinum as the catalyst, produces hydrogen bromide gas, which dissolves readily in water to form hydrobromic acid.

			Platinum
H2(g)	+	Br2(g)	→	2HBr(g)
			heat

4. Displacement of weak or volatile acid from its salt by a strong acid.

Concentrated H₂SO₄ is stronger but less volatile than HCl and, H₂SO₄ can therefore be used to displace the weaker HCl acid from its salt (NaCl).

NaCl_(s)   +  H₂SO_4(aq)   →    NaHSO_4(aq)  +  HCl_(g)

The hydrogen chloride gas formed dissolved in water readily to produce hydrogen chloride acid.

Chemistry SS1 Term 3

EVALUATION

Mention the methods of preparing acids

 

Reaction of Acids (Chemical Properties)

1. Reaction of Acid with Metals

Acid react with some metals to liberate hydrogen gas.

Zn_(s)+ 2HCl _(aq)    →     ZnCl_2(aq) + H_2(g)

Mg_(s)   +  H₂SO_{4 (aq)}   →     MgSO₄+  H_2(g)

NOTE: Dilute HNO₃ does not react with metals to produce hydrogen gas.

2. Reaction of Acids with Base and Alkalis

Dilute acids react with bases and alkalis to form salts and water (known as neutralization reaction)

HCl _(aq) + NaOH _(aq)     →     NaCl _(aq) +  H₂O_(l)

H₂SO_4(aq)  +  CaO_(aq)    →      CaSO_4(aq)  +  H₂O_(l)

3. Reaction of Acids with Trioxocarbonate (iv) and Hydrogen trioxocarbonate (iv).

Acid reacts with CO₃^2-  or  HCO₃^– to liberate carbon (iv) oxide (CO₂).

NaCO_3(s) +  2HCl_(aq)    →    2NaCl_(aq)  +  H₂O_(l)  +  CO_2(g)

NaHCO₃  +  HCl_(aq)    →      NaHCl_l(aq)  +  H₂O_(l)  +  CO_2(g)

 

EVALUATION

1. What is neutralization?
2. State three chemical properties of acids.

 

Uses of Acids

	S/N	Name	Uses
	1	Hydrochloric acid	(i) In industries to make chemicals (ii) To remove rust
	2	Tetraoxosulphate (vi) acid	(i) To make chemicals
			(ii) As drying and dehydrating agent (ii) As drying and dehydrating agent (iii) As electrolyte in lead-acid accumulators
	3	Trioxonitrate (v) acid	(i) For making fertilizers, explosives, etc.
	4	Acetic acid (ethanoic)	(i) In preserving food (ii) In dyeing silk and other textiles
	5	Tartaric	(i) In making baking soda, soft drinks and health salt
	6	Citric acid	(i) in making fruit juice
	7	Fatty acids (e.g. palmitic and stearic acids)	(i) In manufacturing soap. (A process known as Saponification)

EVALUATION

1. Give three (3) uses of each of the following acids: HCl, H₂SO₄, HNO₃, Citric acid
2. Give three physical properties of an acid.
3. Write an equation for the reaction between iron fillings and tetraoxosulphate(vi) acid.
4. State how hydrogen chloride gas can be obtained from tetraoxosulphate (vi) acid
5. (a) What is basicity? (b) State the basicity of the following acids: (i) HNO₃(ii)  H₂SO₄ (iii) CH₃
6. State the natural source of (i) ethanoic acid (ii) Citric acid (iii) Amino acid
7. (a) Why is ethanoic acid regarded as weak acid? (b) Hydrochloric acid is regarded as a strong acid. Why?

 

 

BASES

CONTENT

1. Definition of Bases
2. Strength of an Alkali
3. Characteristics of Bases
4. Preparation of Bases
5. Reaction of Bases
6. Uses of Bases
7. Relative Acidity and Alkalinity (The PH Scale)
8. Logarithmic pH Scale
9. Worked Examples

 

Definition of Bases

A base is a substance which will neutralize an acid to yield salt and water only. It is either an oxide or hydroxide of a metal, e.g sodium oxide, magnesium hydroxide, etc, while; an alkaline is a basic hydroxide which is soluble in water. Bases that are soluble in water are referred to as alkalis. Examples are sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)₂)

Oxides of heavy metals like PbO, ZnO and CuO are insoluble in water and are therefore bases not alkalis. CaO and MgO are slightly soluble and are alkalis. Like acids, alkalis may be strong or weak.

Strength of an Alkali

The strength of an alkali is the degree of its ionization in water. Strong alkalis are completely ionized in water. Examples of strong alkalis are potassium hydroxide, sodium hydroxide, calcium hydroxide, strontium hydroxide etc. Weak alkalis are partially ionized in water . example of a weak alkali is aqueous ammonia,.

Characteristics of Bases

1. Bases are soapy to touch, e.g. NaOH
2. They have bitter taste, e.g. lime water
3. They turn red litmus blue
4. Concentrated form of the caustic alkalis, NaOH and KOH are corrosive
5. They are electrolytes

Preparation of Bases

1. Combustion of a reactive metal in air. When electropositive metals are heated in oxygen, they form metallic oxides.

2Ca  + O₂      →         CaO_(s)

2. By reaction of metals with water (steam)

Ca +  H₂O    →     Ca (OH)₂    +   H₂

3. Decomposition of metal hydroxides by heating

	heat
Ca(OH)2	→	CaO	+	H2O
	heat

Cu(OH)₂    →    CuO  +  H₂O

4. Precipitation or double decomposition reaction

CuSO₄   +   2NaOH   →    Cu(OH)₂   + Na₂SO₄

5. Dissolution of metallic oxides in water

Na₂O + H₂O   →     NaOH

K₂O   +  H₂O    →     2KOH

EVALUATION

1. What is a base? Give three examples.
2. (a) Differentiate between a base and an alkaline. (b) Give three uses of base
3. State three properties of bases and, mention four methods of their preparation with examples.

 

Reaction of Bases

1. Reaction with acid: all bases react with acids to form salt and water only

NaOH + HCl    →     NaCl   +   H₂O

2. Reaction of metallic hydroxide with heat

	heat
Zn(OH)2	→	ZnO	+	H2O
	heat

Reaction with ammonium salts: Alkali reacts with ammonium salts in the presence of heat to liberate ammonia gas.

2NH₄Cl  + Ca(OH)₂     →     CaCl₂  +   2NH₃   +   2H₂O

NaOH   +   NH₄NO₃    →     NaHNO₃    +   H₂O   +    NH₃

 

Uses of Bases

1. NaOH is the most common base and is very soluble, hence it is used as a drying agent.
2. Bases are used in the making of soap.
3. Ca(OH)₂is used in the neutralization of soil acidity.
4. Mg(OH)₂is used in the production of toothpaste.
5. Ca(OH)₂ is used in the making of mortar, plaster of Paris, white wash and cement and sugar refining.
6. NH₄OH is used in weak solution as a common cleanser and grease solvent.
7. NH₃is used in making fertilizers and detergents.

EVALUATION

1. Describe two chemical properties of bases with examples.
2. Give 5 uses of bases with one example each.

Relative Acidity and Alkalinity (The PH Scale)

The term pH denotes hydrogen ion index. It is a number-scale used to express the degree of acidity or alkalinity of a solution and, the number ranges from 0 to 14. A solution with pH value of less than 7 is acidic while that with a value greater than 7 is alkaline. A solution with pH of 7 is neutral i.e. it is neither acidic nor alkaline. The pH of a solution can be measured with an instrument called pH meter.

	Colour	pH Number	Acid/Base
	Red	1 – 3	Very acidic
	Orange	4 – 5	Weak acid
	Yellow	6	Very weak acid
	Green	7	Neutral
	Blue	8	Very weak base
	Indigo	9 – 10	Weak base
	Violet	11 – 14	Very basic

pH Range and Colour Changes of Universal Indicator

Chemistry SS1 Term 3

Logarithmic pH Scale

Sorensen, in 1909, introduced the logarithmic pH scale to eliminate the inconvenience encountered when using negative indices and to give room for wide range of [H⁺]and [OH^–] concentrations that we do come across in acid-base reactions. He defined pH as the negative logarithm of the hydrogen ion concentration to the base 10. For example, if the hydrogen ion concentration of an aqueous medium is 10^-5 mol dm^-3, the acidity of the solution could be written in terms of pH as follows:

[H⁺] = 10^-5

Log [H⁺] = log 10^-5 = −5

pH = −log [H⁺] = − (−5) = 5

Thus, if [H⁺] is 10^-x, then pH = x

Proportional to each other:

[H⁺] [OH⁻]  = 10^-14

P^H+ P^OH = 14, where P^OH is the hydrogen ion index

pOH = 14 – pH

Note: A high pH value indicates low H⁺ concentration (weak acidity) and a high OH^– concentration (strong alkalinity). At neutrality, [H⁺] = [OH^–] = 10^-7

Worked Example

Calculate the pH of 0.005 moldm^-3 tetraoxosulphate (vi).

Solution

H₂SO₄    →     2H⁺ + SO₄^2-

H⁺= [2 x 0.005] moldm^-3

= 0.001 = 1 x 10^-2

pH = −log [H⁺]

pH = −log [1 x 10^-2]

pH = 2

Chemistry SS1 Term 3

EVALUATION

1. (a) Define the term P^H. (b) Calculate the  pH of 0.01 M tetraoxosulphate (VI) acid solution.
2. Mention 3 different methods by which you could prepare bases in the laboratory. Write an equation to illustrate each method.
3. (a). Define pH and P^OH. (b) What is the relation pH and P^OHof an aqueous solution? (c) Determine the pH of a solution containing 0.05moldm_-3 NaCO
4. Distinguish between (i) a strong base and a week base. (ii) a Base and an Alkaline.
5. A glass cup of orange juice is found to have P^OHof 11.40. Calculate the concentration of the hydrogen ions in the juice.
6. Find the hydrogen ion, H⁺and hydroxide ion, OH^– concentration in 0.02M solution of H₂SO₄.

 

Chemistry SS1 Term 3

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