10 sci chp 2 revsn ntes

10 SCIENCE REVISION NOTES   

            CHAPTER 1 CHEMICAL REACTIONS AND EQUATIONS     

★ Based on chemical properties substances are classified as Acids, Bases and  Salts.

★ Acids prepared from minerals are called mineral acids

Examples: Hydrochloric acid - HCI,  Sulphuric acid - H₂SO_4, Nitric acid - HNO₃

★ Acids present in plants and animals are called organic acids

Examples: Lemon -citric acid, Tomato - oxalic acid, Tamarind - tartaric acid, Ants - Formic acid

★ Some other organic acids are:

Methanoic acid - CH₃COOH

Ethanoic acid - C₂H₅COOH

Benzoic acid - C₆H₅COOH

Formic acid - HCOOH

Indicators: An indicator is a dye that changes colour when it is put into an acid or a base

Types of indicators:

→ Natural indicators - Examples: litmus, turmeric, cabbage etc.

→ Synthetic indicators - Examples: phenolphthalein, methyl orange.

→  Olfactory indicators - Examples: Onion, vanilla, clove

→ Universal indicator - It is a mixture of several indicators

Properties of Acids:

→ Acids are sour to taste.

→ They turn blue litmus to red

→ Acids have hydrogen ions

→ They conduct electricity.

→ Acids react with bases to form salt and water.

→ Sulphuric acid reacts with zinc metal and liberates hydrogen gas.

When a candle is introduced into a soap bubble containing hydrogen gas, 'popping' sound is heard with a small explosion, indicating the gas liberated is hydrogen.

Zn(s)+H₂SO₄(aq) → ZnSO₄(aq) +H₂(g)

Note: Metals displace hydrogen from acids. All compounds which contain hydrogen are not acids

→ Hydrochloric acid reacts with metallic carbonate and metallic hydrogen carbonate to give carbon dioxide and sodium chloride.

Na₂CO₃ + 2HCI → 2NaCI + H₂O + CO₂

NaHCO₃ + HCI → NaCI + H₂O + CO₂

To know that CO, is liberated, pass the gas through lime water; where lime water turns milky.

Ca(OH)₂ (aq) + CO₂(g) → CaCO₃(s)+H₂O(l)

lf excess CO, is passed, then the following reaction takes place

CaCO₃(s) + H₂O (l) + CO₂(g) → Ca(HCO₃)₂

→ Reaction with metallic hydroxides:

2NaOH(aq) + H₂SO₄(q) → Na₂SO₄(aq) +2HO(l)

Ca(OH)₂(aq) + 2HCI(aq)  → CaCl₂(aq) + 2H₂O(l)

→ Neutralisation reaction: When an acid reacts with a base, salt and water are formed. This reaction is called neutralisation reaction.

NaOH (s) + HCI(aq) → NaCl(aq) + H2O(l)                                                                                                                 

Ca(OH)₂ + H₂SO₄  → CaSO₄ + 2H₂O                                                                                                                        

→ Conduction of electricity by acids:

When an acid dissolves in water it gives hydrogen (H⁺) ions or hydronium ions (H₃O⁺ ). Because of the formation of these ions acids conduct electricity in aqueous solution.

HCI  → H⁺ + CI^- (H⁺ hydrogen ion)

H⁺ + H₂O  → H₃O⁺ (H₃O⁺ hydronium ion)

Note:

→ Organic acids are non-conductors of electricity as they do not dissociate into ions

Examples: Formic acid - HCOOH, Methanoic acid - CH₃COOH, Ethanoic acid - C₂H₅COOH

→ Dilution of an acid is an exothermic reaction. Therefore acid is to be added slowly to water taken in a beaker with constant stirring. Suddenly adding acid to water causes splashing the acid which can cause burning of the skin In dilution of acids or bases H+ or OH- ions decrease per unit volume.

Properties of Bases:

→  Bases are bitter to taste.

→  Bases dissolve in water. A base which dissolves in water is called alkali.

→  Bases turn red litmus to blue.

→  Bases when dissolved in water give hydroxide ions (OH^- ions).

→ Bases react with acids to give salt and water.

2NaOH(aq) + H₂SO₄(aq) →  Na₂SO₄(aq)  + 2H₂O(l)  

KOH(aq) +HCI(aq) →   KCI (aq) + H₂O(l)  

→  Bases conduct electricity in their aqueous solution

pH Scale and pH Value:

→  The strength of an acid or a base is measured on a scale of numbers having values from 0 to 14. This is called pH scale and the numbers are called pH values.

→  pH has no units. It is a value which indicates how strong is an acid or a base.

→ Neutral substances or solutions have pH exactly 7

→ Acids have pH value less than 7.

→ Bases have pH value more than 7

→ A strong acid has a lower pH than a weak acid. A strong base has a higher pH than a weak base

→ Blood is slightly alkaline because occause its its pH pH is is 7.3.

→ pH value value of ofacia acid rain is less than 5.6.

→ Corrosion of teeth starts when pH of mouth is below 5.5 (tooth decay) on pain. Stinging the To sting hair of to counteract nettle counteract this, leaves the baking inject pain soda of methanoic (an the alkali) bee-sting. acid, is causing rubbed

→ Toothpastes which are alkaline are used to clean the teeth by neutralising the excess of acid in food to prevent tooth decay.

→ Antacids such as 'Milk of magnesia' are often used to neutralise excess of acid in our stomach

Salts

Common salt: Sodium chloride - NaCI

It is obtained by the evaporation of sea water. Common salt is used in obtaining various substances which are used in our daily life.

Caustic soda: Sodium hydroxide - NaOH

It is obtained by passing electricity through sodium chloride solution (brine). This process is called chloro-alkali process because of the formation of chlorine and sodium hydroxide, which is an alkali.

de-greasing

Uses: Used in making soaps, detergents, metals, paper manufacturing and making artificial fibres.

Bleaching powder: Calcium oxychloride CaOCl₂ 

It is produced by the action of chlorine on dry slaked lime.

Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Uses: Used in bleaching cotton, wood pulp and clothes. Used as an oxidising agent in chemical industry and in chlorination of drinking water to make it free from germs.

Baking soda: Sodium hydrogen carbonate - NaHCO₃

It is produced by reacting sodium chloride with carbon dioxide and ammonia

NaCI + H₂O + CO₂ + NH₃ → NH₄CI+ NaHCO₃

When heated with water it produces carbon dioxide.

NaHCO₃ + H⁺ (from an acid) → CO₂ + H₂O + sodium salt of acid

Uses: CO₂  makes bread or cake to rise, making them soft and spongy. Therefore it is used in bakeries. It is used as an ingredient in antacids and soda-acid fire extinguishers

Note: NaHCO₃  + Tartaric acid is used as baking soda.

Washing soda: Sodium carbonate - Na₂CO₃ .10H₂O

Sodium 'carbonate is obtained by baking soda and by recrystallisation.

Na₂CO₃ + 10H₂O →  Na₂CO₃.10H₂O

Uses:

→ Used in the manufacturing of glass, soap and paper industry, manufacturing of Borax.

→ Used as cleaning agent at domestic level and removing hardness of water.

in on a v.C.) 

Water of crystallisation:

Water of crystallisation is the fixed number ber of of water molecules present in one formula unit of salt.

Example:

Copper sulphate - CuSO₄.5H₂O W.C. is 5.

Plaster of Paris 

Calcium sulphate hemihydrate- CaSO₄ ½ H₂O

It is a white powder obtained from heating gypsum at 373 K. It loses water molecule and gives plaster of paris.

CaSO₄.2H₂O  →  CaSO₄. ½ H₂O + 1 ½ H₂O

Uses: Used to support bone fractures in medicine. Used in making toys, decorative ceilings and for making smooth surfaces

Note: Plaster of Paris should be kept away from moisture because it sets into a hard solid mass.