Chp -2 Acid Bases And Salts

Question 1

what are acids and what are some physical characteristic propertires of it?

Answer 1

The word acid has been derived from the latin word 'acidus" meaning sour to taste.
. Acid is the substance which when dissolved in water, ionizes and releases hydrogen ions or hydronium ions (H3O)  in the soln .
HCL(aq)---> H+ + Cl-
HCL+ H2O---> H3O+  + Cl- 
properties of acids-
- taste sour
corrosive on ksin
-good conductor of electricity
-exothermic when diluted

Question 2

write a note on litmus and name other natural indicators

Answer 2

litmus soln is a purple dyet, which is extracted from lichen, a plant belonging to the division thallophyta and i s commonly used as an indicator. When the litmus
solution is neither acidic nor basic, its colour is purple. There are many other natural
materials like red cabbage leaves, turmeric, coloured petals of some flowers such as
Hydrangea, Petunia and Geranium, which indicate the presence of acid or base in a
solution. These are called acid-base indicators or sometimes simply indicators.

Question 3

what are indicators and olfactory indicators? give exampls

Answer 3

An indicator is an dye that changes colour when it is put into an acid and a base. Olfactory indicators are those indicators that help to identify whether the given solution is acidic or basic by changing their smell instead of colour as other indicators do. For example onion, vanilla extract, clove, etc
Onion: Paste or juice of onion loses its smell when added with base. It does not change its smell with acid.
vanilla: smell of vanilla vanishes with base.

Question 4

what are the effects acids and bases have on indicators

Answer 4

ACIDS- 
-blue litmus red
- methyl orange-red
-phenolphthalein- colourlesss in acids
turmeric paper- no change
BASES- 
-red litmus blue 
-methyl orange yellow 
- phenolphthalein- pink 
-turmeric paper reddish brown

Question 5

explain how acids react with metals, how base react with metals

Answer 5

Acids + metal → salt+ h2
Fe+ H2SO4 →FeSO4 + H2

Bases + metals -
Metals like zinc tin and aluminium react with strong alkali like caustic  soda and Caustic potash to evolve hydrogen gas
-2NaOH(aq) +Zn (s)→ Na2ZnO2(S)+ H2
- 2 Al + 2NaOH —-> Na2ZnO2+ H2 
-Sn + 2NaOH —-> Na2SnO2 + H2

Question 6

dry HCL is not acidic. why?

Answer 6

The acidic behaviour of acids is due to the presence off hyydrogen ions. The acids produce hydrogen ions only in the presence of water.(H3O). So, in the basence of water, a substance will not form hydrogen ion and hence HCL wont show the acidic property. Y

Question 7

classify acids on the basis of sources

Answer 7

1)minerals acids- obtained from rocks and minerals. All mineral acids are strong except carbonic acid(used in fizzy soft drinks n soda water)
for exampls- HCL,H2SO4, HNO3, H2CO3, H3PO4
2)Organic acids-obtained ffrom plant and animals .
for eg- formic acid, acetic acid ,benzoic acid, citric acid.

Question 8

what is basicity?

Answer 8

Basicity of an acid is determined by no. of hydronium ion /h+ produced per molecule of an acid on complete ionisation.

Question 9

classify acids on the basis of their basicitry

Answer 9

1) monobasic acids- on emolecule of acid gives one hydronium ion.Cfor eg- HCL,Hbr,etc.
2) dibasic acids- one molecule of acid gives two hydronium ion. H2SO4, H2CO3
3) Tribasic acid- one molecule of acid gives 3 hydronium ion.H3PO4, citric acid (C6H8O7)

Question 10

Classify acids on the basis of their strength

Answer 10

Strong acids: they undergo complete ionisation in aqueous solutions.
Strong acids also have a high electrical conductivity because of the high concentration of hydrogen ions in their solution. Thus, all the strong acids are strong electrolytes.
For example: HCL,H2SO4.

Weak acids : they undergo incomplet ionisation in aqueous solution.
• Due to a small amount of hydrogen ions present in their solutions, weak acids react quite slowly with other substances (such as metals, metal carbonates and metal hydrogencarbonates, etc.).
•Weak acids have low electrical conductivity because of the low concentration of hydrogen ions in them
For example_ CH3COOH(acetic acid) HCOOH, H2CO3(carbonic acid) H2SO3(sulphurous acid)

Question 11

classify acids on the basis of concentration

Answer 11

concentrated- they have less amount of water and more amount of acid.
Dilute- they have more water and less acid.

Question 12

what are bases and alkalis? give some physical prop.

Answer 12

according to arrhenius theory” Those substances which give hydroxide or hydroxyl ion in their aqueous solutions are called bases”.
NaOH(aq) → Na+(aq) + OH-
•All metal oxides and metal hydroxides are bases.
•metal carbonates and metal hydrogencarbonates are also considered to be bases because they neutralise the acids hus, sodium carbonate (Na2CO3)calcium carbonate (CaCO3,) and sodium hydrogen carbonate (NaHCO3) are also bases.
•bases which are completely dissolvable in water are called alkalis.for eg-NaOH,KOH.
properties-
-bitter to taste
-soapy texture
-good conductors of electricity
-release heat when diluted

Question 13

Uses of bases

Answer 13

Sodium hydroxide is used in the manufacture of soap, paper and a synthetic fibre called ‘rayon’.

2. Calcium hydroxide (called slaked lime) is used in the manufacture of bleaching powder.
3. Magnesium hydroxide is used as an ‘antacid’ to neutralise excess acid in the stomach and cure indigestion.
4. Sodium carbonate is used as washing soda and for softening hard
5. Sodium hydrogencarbonate is used as baking soda in cooking food, for making baking powders, as an antacid to cure indigestion Ammonia solution and in soda-acid fire extinguishers.

Question 14

Is acid is present on other planets

Answer 14

The atmosphere of planet Venus is made up of thick white and yellowish Clouds of sulphuric acid. So life cannot exist on the planet Venus

Question 15

What is the acidity of a base

Answer 15

acidity of a base is determined by the no. of hydroxyl_OH-) Ion produced per molecules of a base or alkali on complete dissociation in water.

Question 16

t/f 1)The strength of an acid depends on concentration of acid And on dilution strength of acid or base
increases
2s long as baking powder is dry, the sodium hydrogencarbonate and tartaric acid present in
it do not react with each other.
3)baking soda and baking powder are single compounds

Answer 16

1)F: depends on the concentration of hydronium ion And on Dilution strength of acid or base decreases.
2) T
3)FALSE:Baking soda is a single compound : sodium hydrogencarbonate. On the other hand, baking powder is a mixture of sodium hydrogencarbonate and a
solid, edible acid such as tartaric acid (or citric acid)

Question 17

Classify bases on the basis of acidity-

Answer 17

Mono acidic bases-= produce 1 hydroxyl ion per molecule. NaOH, KOH,.
Diacidic- produce 2 hydroxyl ion per molecule
CaOH)2, Ba(OH)2, Mg(OH)2
tri- acidic- produces 3 hydroxyl ion per base molecule. Al(OH)3, Fe(oh)3

Question 18

Classify bases on the basis of strength

Answer 18

1) strong bases- undergo completer ionisation in aqueous soon. Do eg- NaOH,KOH, CaOh)2
2) weak bases- Undergo incomplete ionisation in aq soln. For eg- NH4OH, Al(OH)3,etc

Question 19

Classify bases on the basis of concentration

Answer 19

Concentrated- contain less amount of water and more amount of base
Dilute- large amount of water and less amount of baseboard

Question 20

What is caustic potash and caustic potash and soda ash

Answer 20

Bases like NaOH and KOH have corrosive nature that is they are caustic, so are known as caustic soda b caustic potash.
anyhydrous sodium crabonate is genrally called soda ash( one the source is ashes of plants)

Question 21

While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Answer 21

When a concentrated acid is added to water for preparing a dilute acid, then the heat is evolved gradually and easily absorbed by the large amount of water (to which the acid is being added) however if water is added to concentrated acid, then large amount of heat is evolved at once. This heat changes some of the water to steam explosively which can splash the acid on our face or clothes and cause acid burns. Even the glass container may break due to the excessive heating.

Question 22

What happens on passing excess CO2 through the solution of calcium carbonate

Answer 22

CaCO3 +H2O +CO2 —-> Ca(HCO3)2

Question 23

Define neutralisation and endpoint

Answer 23

Neutralisation maybe defined as the reaction between acid and base present in aqua solution to form salt and water. Neutralisation is the combination of hydrogen ion of an acid and hydroxyl ion of a base to form water

The complete neutralisation of an acid solution by a base and vice versa is indicated by sudden change in the colour of the indicator present. This is called endpoint. It implies that H+ irons of the acid have completely reacted with hydroxyl irons of the base to form water which is neutral

Question 24

Fill in the blank-

1) Egg shells contain ____ as the main constituent due to which it reacts with acids
2) Organic tissues like skin etc get completely Completely corroded by____ (hydrogen, carbon monoxide, alkalis, acids)
3) NH3 gas is ___in nature (acidic/basic / neutral).
4) Saliva is of ____ nature (acidic/ alkaline/ neutral).
5) H2S is weakly ____ in nature (acidic/ basic/ neutral).
6) Some metal oxides like- ___,___and ___are neutral

Answer 24

1) Calcium carbonate
2) alkalis like NaOH & KOH
3) Basic
4) alkaline
5) acidic
6) NO, CO, N2O

Question 25

List some common use of mineral acids

Answer 25

1. Sulphuric acid- used in the manufacture of fertilisers (like ammonium sulphate), paints, dyes, chemicals, plastics, synthetic fibres, detergents, explosives and car batteries.

2.Nitric acid is used for making fertilisers (like ammonium nitrate), explosives (like TNT: Tri-Nitro
Toluene), dyes and plastics.

3. Hydrochloric acid is used for removing oxide film from steel objects before they are galvanised) and for removing ‘scale’ deposits from inside the boilers. It is also used in dye-stuffs, textile, food, plastic and leather industries.
4. phosphoric acid – used in antirust paints and fertilisers

Question 26

explain how acids react with metal carbonates and metal hydrogen carbonate

Answer 26

carbonates/hydrogen carbonates +acids → Salt +CO2+ H2O

• Na2CO3(s) +2HCL→ NaCl(aq)+CO2+H2O
• NAHCO3+ HCL→ NaCl +H2O +co2

Question 27

Plane how acid and base react with each other

Answer 27

Acid+ base → salt +H2O

• NaOH+ HCL→ NaCl +H2O
• HNO3 + KOH —-> KNO3 +H2O
• HCL + NH4OH—-> NH4Cl + H2O

Question 28

explain how metal oxides react with acids and non-metallic oxides react with base. Name few non metallic oxides

Answer 28

Metal oxide+ Acid → salt+ H2O
CaO + H2SO4—> CaSO4 +H2O
CuO + 2HCL→ CuCl2 +H2O

Non metallic oxide+ base→ salt +H2O
Ca(OH)2 + CO2—> CaCO3 + H2O
2NaOH + CO2 —> Na2CO3 + H2O 
2KOH + CO2 —> K2CO3 + H2O 
CO2, SO2, SO3 r non- metallic oxide. They are acidic in nature.

Question 29

Differentiate between acids and bases

Answer 29

ACIDS - Sour in taste
BASES- better in taste

ACID – the properties are due to presence of hydrogen ion in the aqueous soln of acid
BASIS – the properties are due to presence of hydroxyl ions in water solution of base

ACID– turn blue litmus reD
BASES – turns red litmus blue

ACID – an aqua solution conduct electricity
BASES- aqua solution conduct electricity

ACID – reacts with active metals like sodium, potassium, calcium and zinc to give hydrogen gas BASES-Does not react with metals except zinc, aluminium and Sn.

ACIDS: react with carbonates to give carbon dioxide BASEs absorbs carbon dioxide to form carbonate

ACID frequently corossive of the skin
BASCS frequently corrosive the skin and slippery nature
ACID the pH value is less than seven at 25°C
BASES- The pH value is greater than 7 at 25° C

Question 29

What is deliquescence

Answer 29

Certain crystalline substances when exposed to atmosphere absorb moisture and change into solution. The Absorption of moisture from air to form a solution is called Deliquescence. Sodium hydroxide, potassium hydroxide, calcium chloride etc a deliquescent substances.

Question 30

What are hygroscopic substances

Answer 30

Certain substances absorb water from atmosphere without undergoing change in physical state. Such substances are known as hygroscopic substances.
Anhydrous sodium carbonate, and Anhydrous copper sulphate, Concentrated sulphuric acid are examples of hygroscopic substances

Question 31

What happens when water is mixed with an acid Orabase

Answer 31

Mixing of acid or base in water is called Dilution. During Dilution the concentration of ions per unit volume decreases. This process generally exothermic in nature which produces heat. Heat produced maybe harmful because it may cause mixture of splash out and cause burns

Question 32

what is the ph scale? Who devised it?

Answer 32

•both acidic solutions as well as basic solutions contain hydrogen ions.
• In 1909 Sorenson devised a scale (known as pH scale) on which the strength of acid solutions as well as basic solutions could be represented by making use of the hydrogen ion concentrations in them.
•Sorenson linked the hydrogen ion concentrations of acid and base solutions to the simple numbers 0 to 14 on his pH scale.
•The pH of a solution is inversely proportional to the concentration of hydrogen ions in it. That is, a solution having a high concentration of hydrogen ions has a low pH value. On the other hand, a solution having lote concentration of hydrogen ions has a high pH value.
• In the term pH, letter P for a German word ‘potenz’ which means ‘power and letter H stands for hydrogen ion concentration.
•It is a pure no., it has no units
1 ) solutions with pH =0-3 are strongly acidc, with PH =3-5 are moderately acidic while with pH = 5-7 are weakly acidic.
2) solutions with ph = 7-9 are weakly basic and pH=9-12 are moderately basic wile the pH= 12-14 are strongly basic
3) if pH =7 soln is neutral.

Question 33

what is ph OF BLOOD?

Answer 33

The ph of blood varies between 7.36 to7.42. it is maintained by soluble hydrogen carbonates and carbonic acid present in our blodd. these are known as buffers. in general the role of buffer to control the pH of blood

Question 34

explain the importance of pH in plants and animals

Answer 34

Our body works within the pH range of 7.0 to 7.8. Living organisms can survive only in a narrow range of pH change. for eg- When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.Calcium carbonate is often added to acidic lake water can neutralise the acid.com from acid rain

Question 35

explain the importance of pH of soil

Answer 35

Plants require a specific pH range for their healthy growth. actually diiferent plants prefer different pH soil therefor it is importanat to give plant speciifc pH soil. the ideal soil pH should be 7. however soils with high peat content or iron mineral or with rotting vegetable tend to become acidic. the pH of acidic soil cn reach as low as 4 and that of basic soil can go upto 8.3.

Question 36

importance of pH in our digestive system

Answer 36

our stomach produces gastric juices that contain hydrochloric acid. It helps in the digestion of food without harming the stomach.
sometimes excess of acid is produced in stomach due to overeating or eating pspicy food. this stage is called acidity.During indigestion the stomach produces too much acid and this causes pain and irritation. To get rid of this pain, we take antacids. Antacids are a group of mild bases which have no toxic effects on the body. Being basic in nature, antacids react with excess acid in the stomach and neutralise it. This gives relief to the person concerned. The two common antacids used for curing indigestion due to acidity are: Magnesium hydroxide (Milk of Magnesia) and Sodium hydrogencarbonate (Baking soda)

Question 37

explain how ph change causes tooth decay

Answer 37

generally ph of mouth is more than 7 due to saliva which basic in nature. however when we eat food , some food particles remain in the mouth and bacteria present in our mouth produces acids by degradation of food particles
.Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. lactic acid is one of these acids.Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and
prevent tooth decay

Question 38

how is pH used in self defence by animals and plants

Answer 38

Bee-sting leaves formic acid(methanol acid) which causes pain and irritation. Use of a mild base like baking sodaon the stung area gives relief.
When a wasp stings, it injects an alkaline liquid into the skin. So, if a wasp stings a person, then rubbing a mild acid like vinegar on the stung area of the skin gives relief. This is because, being an acidic substance, vinegar neutralises the alkaline liquid injected by the wasp sting and cancels its effect. a bee’s sting is acidic whereas wasp sting is alkaline in nature.
An ant’s sting injects methanoic acid into the skin of a person causing burning pain. Being acidic, an ant’s sting can be neutralised by rubbing a mild base

in the plant kingdom, Nettle is a herbaceous plant which grows in the wild. Its leaves have stinging hair, which cause painful stings when touched accidentally. This is due to the methanoic acid(HCOOH) secreted by them. nature provides remedy in the form of dock plant which often grows near nettle and some basic chemicals

Question 39

Some plants have their own indicators.

Answer 39

for eg- th eflowers of a hydrangea bush are blue in colour in colour when grown in acidic soil. If it is alkaline in nature, the flower is pink.
Red cabbage- red in colour- remains red in acid but turns green in basic

Question 40

what are the families of common salt

Answer 40

1) On the basis iof commo acids
-sulphates= K2SO4, Na2 SO4,Caso4 , MgSO4, cUSO4=
- chlorides = NaCl, nh4cl
Carbonates-= Na2CIO3
2) On the basis of comon base
sodium salts= Na2SO4, nACL , nAno3, Na2CO3
Potassium salts= K2SO4
Ca salts = CaSO4
Mg salts= MgSO4
CU= CuSO4
NH4 salts= NH4Cl

Question 41

what are salts and how are they formed

Answer 41

salts are ionic compound( must have metal n nm) consiting of two prats, one carrying a posiive charge called cation and the other part carrying a negative charge called anion.Salts are mostly solids. They have high melting points and boiling points. Salts are usually soluble in water. Just like acids and bases, solutions of salts in water conduct electricity. That is, salts are electrolytes.
Salt solutions conduct electricity due to the presence of ions in them
formation of salts-
↪by neutralistion
for eg-n NaOH + hcl → NaCl +H2O
↪by action of metals on acids
hcl+fe →FeCl)3 + H2
↪by action of acids on metal carbonates and bicabonates
for eg- CaCO3 + HCL → CaCL2 + CO2 + H20
↪by cation of metals on alkalis
for eg- 2NaOH + Zn —-heat ⇒ Na2ZnO2b + H2

Question 42

t/f +ion r always metal ion

Answer 42

false; they generally are except for ammonium ion

Question 43

give iwth example the acidic salt, basic salt and neutral salt.

Answer 43

◉Salts of a strong acid and a strong base
are neutral with pH value of 7.
for eg- sodium hydroxide + hcl

◉salts of a strong acid and weak base
are acidic with pH value less than 7
for eg- ammonium hydroxide+ HCL

◉salt of weak acid and strong base are basic in
nature, with pH value more than 7.
for eg-2NaOH (aq) + H2CO3 (aq—->Na2CO3 (s) + 2H2O for eg-
sodium acetate (CH3COONa)- formed from a weak acid acetic acid (CH3COOH), and a strong base sodium hydroxide (NaOH

◉salt of weak acid and weak base
for eg- CH3COOH + NH4OH→ CH3COONH4+ H2O
acetic acid+ ammonium hydroxide→ ammonium acetate

Question 44

how is sodium hydroxisde formed and how are the by products commercially useful

Answer 44

Commercial name: Caustic
soda
● Raw material : NaCl and water
● Principle: NaOH is a strong
base and is prepared by the
electrolysis of aq solution of
NaCl which is called as brine.
●electrolysis of brine is carried out in an electrolytic cell known as Nelson’s cell. This process is called chlor alkali because chlorine and NaOH are formes
2NaCl(aq) + 2H2O 🡪 2NaOH(aq) + Cl2(g) +H2(g)
● On electrolysis , chlorine gas is formed at anode and hydrogen at cathode
● NaOH solution is formed near the cathode.
Hydrogen- as fuel, for manufcaturing ammonia for fertillizers;used in the hydrogenation of oils to obtain solid fats ;Liquid hydrogen is used as a fuel for rockets.

Chlorine- in water treatment, swimming pools, and manufacturing PVC, disinfectants, CFCs, and pesticides
.
Naoh- in manufacture of soap and detergents, paper making and artificial fibers like rayon ;in purifying bauxite ore from which aluminium metal is extracted;de-greasing metals, oil refining, and
making dyes and bleaches
The two products of chlor-alkali process, sodium hydroxide and chlorine, combine together to produce
another chemical called sodium hypochlorite (NaClO). Sodium hypochlorite is a bleaching agent which is
used in making ‘household bleaches’ and for ‘bleaching fabrics’.

Question 45

how is baking soda formed? state its uses

Answer 45

Chemical name and formula: Sodium hydrogen carbonate or sodium bicarbonate.(NaHCO3)
● Commercial name: baking soda
- Lab method: baking soda can be prepared by saturating a cold solution of sodium carbonate with carbon dioxide.
Na2CO3(aq)+CO2(g)+H2O (l) 🡪 2NaHCO3
-Industrial method: NaHCO3 is obtained as intermediate product in the Solvey process for the manufacture of sodium bicarbonate from common salt.
• NaCl)+CO2)+H2O+ NH3 🡪 2NaHCO3(aq) +NH4Cl (s)
uses-
for making baking powder which is a mixture of baking soda (sodium hydrogencarbonate) and a mild edible acid such as tartaric acid
Carbon dioxide produced during the reaction can cause bread or cake to rise making them soft and spongy.
(ii) Sodium hydrogencarbonate is also an ingredient in antacids. Being alkaline, it neutralises excess acid in the stomach and provides relief.
(iii) It is also used in soda-acid fire extinguishers.

Question 46

how is bleaching powder formed and state its uses

Answer 46

Chemical name and formula: Calcium oxychloride or calcium hypochloride (CaOCl2) or chloride of lime.
● Preparation of bleaching powder: it is prepared by the action of chlorine gas on dry slaked lime.
● Ca(OH)2 + Cl2 🡪 CaOCl2 + H2O
● On industrial scale it is prepared by “Hasen-clever plant”
uses-
(i) for bleaching cotton and linen in the textile industry, for bleaching(the real bleaching agent present in bleaching powder
is chlorin);
wood pulp in paper factories and for bleaching washed clothes in laundry;
(ii) as an oxidising agent in many chemical industries; and
(iii) to make drinking water free from germs.
4)in rendering wool unshrinkable
5)in manufacture of choroform(CHCl3)

Question 47

are crystals really dry?

Answer 47

Crystal of some salts contain amount of associated water.
● The water associated with crystal of any salt is called water of crystallisation. it is the fixed number of water molecules present
in one formula unit of a salt.for eg
blue vitriol- Cuso4.5H20
green vitriol- FeSO4.7H2O
White vitriol- ZnSO4.7H20
gypsum- CaSO4.2H2O
● the salt containing water of crystallisation are called hydrated.

Question 48

what is washing soda and what are its uses

Answer 48

Chemical name: Sodium carbonate decahydrate (Na2CO3.10H2O)
It is obtained by heating baking soda which is obtained by passing CO2 gas through NaCl solution saturated with ammonia.
Recrystallization of sodium carbonate gives washing soda.
Na2CO3 +10H2O –Na2CO3.10H2O
properties-
1)When freshly prepared it is a transparent crystalline solid containing ten molecules of water of crystallisation.
2) if kept open in air the crystal o washing soda lose nine molecules of water crystallisation to form a monohydrate which is a white powder.
3) is one of the few metal carbonates which are soluble in water
4) The solution of washing soda in water is alkaline which turns red litmus to blue.
usess-
i) Sodium carbonate (washing soda) is used in glass, soap and paper industries.
(ii) It is used in the manufacture of sodium compounds such as borax.
(iii) Sodium carbonate can be used as a cleaning agent for domestic purposes.
(iv) It is used for removing permanent hardness of water.

Question 49

Give the pH value of 
Concentrated hydrochloric acid
2. Dilute hydrochloric acid
Gastric juices (Digestive juices in stomach)
4. Lemon juice
5. Vinegar 
6. Tomato juice
7. Coffee
8. Soft drinks
9. Milk
10. Pure water
Saliva (before meals)
12.After meal
13.blood
14. Eggs
15. Toothpaste
16. Baking soda
17. Washing soda solution
18. Milk of magnesia
19. Household ammonia
20. Dilute sodium hydroxide
21. Concentrated sodium hydroxide

Answer 49

Solution

1. Concentrated hydrochloric acid- 0
2. Dilute hydrochloric acid-1
3. Gastric -1.4
   (Digestive juices in stomach)
4. Lemon juice 2.5
5. Vinegar- 4.0
6. Tomato juice- 4.1
7. Coffee- 5.0
8. Soft drinks 6.0
9. Milk- 6.5
10. Pure water- 7
11. Saliva (before meals)7.4

Saliva (after meals) 5.8

13. Blood-7.4
14. Eggs-7.8
15. Toothpaste- 8
16. Baking soda solution8.5
17. Washing soda solution 9

18 Milk of magnesia 10.5

Household ammonia-11.6

Dilute sodium hydroxide- 13

Concentrated sodium hydroxide-14

Question 50

How is POP formed

Answer 50

POP is hemihydrate (Hemi means half and hydrate means water) of calcium sulphate.
• Formula: CaSO4.1/2 H2O Or (CaSO4)2.H2O
● Preparation of POP: It is obtained by heating gypsum (CaSO4.2H2O) in at 373K( gypsum loses three-fourths of its water of crystallisation. )
-CaSO4.1/2 H2O + 1.5 H2O → CaSO4.2H2O
PROPERTIES-
-white, odourless powder
-at ordinary temp, POP absorbs moisture and a large amount of heat is genrated.
- when mixed with a limited amount of water, it forms plastic mass, evolves heat and quickly sets to a hard porous mass within minutes. this is calle setting process.during setting a slight expansion in volume occurs. it is due to thios that it fills the mould completely giving a sharp impression.
-The temperature during the heating of gypsum should not be allowed to go above 100°C (or above 373 K). This is because if gypsum is heated above 100°C (or above 373 K), then all its water of crystallisation is eliminated and anhydrous calcium sulphate (CaSO4) called dead burnt plaster is formed. The anhydrous calcium sulphate
(or dead burnt plaster) does not set like plaster of Paris on adding water
USES-
-making casts and patterns for moulds and statues.
-used as cement in ornamental casting
-as fire proofing material and for chalks
-in hospital for immobalising the affected part in case of fracture or sprain
- fill gaps on walls and roofs.
In India gypsum is found in large quant. in Punjab n Rajasthan.

Question 51

List the Colours produced by a universal indicator at various pH values

Answer 51

0- ark red 
1- red 
2 red 
3 orange red 
4 orange
5 orange yellow 
6 greenish yellow
7 green
8 greenish blue
9 blue
10navy blue
11purple 
12 dark purple 
13 violet
14- violet

Question 52

Why does distilled water not conduct electricity whereas rain water does?

Answer 52

Distilled water does not conduct electricity because it does not contain any ionic compounds dissolved in it whereas rain water does.
Reason: When rain water falls on earth through the atmosphere, it dissolves an acidic gas ‘carbon dioxide’ from the air and forms carbonic acid (H2CO3). The carbonic acid provides some hydrogen and carbonate ions to the rain water. Due to the presence of these ions, rain water conducts electricity.

Question 53

explain why Nh4Cl urns blue litmus paper red?

Answer 53

hydrochloric acid is a strong acid which is fully ionised and gives a large amount of hydrogen
ions [H+(aq)]. On the other hand, ammonium hydroxide is a weak base which is only slightly ionised and
gives a small amount of hydroxide ions [OH–(aq)]. Since ammonium chloride solution contains more of
hydrogen ions than hydroxide ions, it is a.acidic in nature. It turns blue litmus red. Another example of a salt which gives an acidic solution is ammonium sulphate (NH4)2SO4. It is formed from a strong acid sulphuric
acid (H2SO4) and a weak base ammonium hydroxide (NH4OH).cidic in nature

Question 54

Sources of common salt

Answer 54

The main source of common salt (sodium chloride) is the sea water. Sea water contains about 3.5% of soluble salts, the most common of which is sodium chloride (2.7 to 2.9%). Saline water of inland lakes, such as Sambhar lake in Rajasthan is also a good source of common salt.

Underground deposits of common salt are found in many parts of the world. The large crystals of common salt found in underground deposits are called rock
salt. Rock salt is usually brown due to the presence of impurities in it. Rock salt is mined from the underground deposits just like coal. The rock salt which we dig out today from the earth was formed when the ancient seas dried up by evaporation, thousands of years ago.

Question 55

what are the uses of salt?

Answer 55

. Common salt (sodium chloride) is used as a raw material for making a large number of useful chemicals
in industry such as : sodium hydroxide (caustic soda), sodium carbonate (washing soda), sodium
hydrogencarbonate (baking soda), hydrochloric acid, hydrogen, chlorine, and sodium metal.
2. Common salt (sodium chloride) is used in cooking food. It improves the flavour of food. Sodium
chloride is required by our body for the working of nervous system, the movement of muscles, and the
production of hydrochloric acid in the stomach for the digestion of food.
3. Common salt (sodium chloride) is used as a preservative in pickles, and in curing meat and fish
(preserving meat and fish).
4. Common salt (sodium chloride) is used in the manufacture of soap.
5. Common salt (sodium chloride) is used to melt ice which collects on the roads during winter in cold
countries.

Question 56

while baking can we just use either baking soda or baking powder?

Answer 56

When baking powder mixes with water (present in dough made for baking
cake or bread), then sodium hydrogencarbonate reacts with tartaric acid to evolve carbon dioxide gas.
-The carbon dioxide gas produced gets trapped in the wet dough and bubbles out slowly making the
cake (or bread) to ‘rise’ and become soft and spongy.
- If, however, baking powder is not added in the
preparation of cake (or bread), then the cake (or bread) obtained will be hard and quite small in size.
-If only sodium hydrogencarbonate (baking soda) is used in making cake (or bread), then sodium carbonate formed from it by the action of heat during baking) will give a bitter taste to cake (or bread).
-The advantage of using baking powder is that tartaric acid present in it can react with any sodium carbonate formed and neutralise it. And the sodium tartarate salt
formed by neutralisation has a pleasant taste

Question 57

What is efflorescence?

Answer 57

Certain hydrated crystalline salts when exposed to atmosphere lose their water of crystallisation spontaneously and change into amorphous powder
This process is called efforescence and the substances exhibiting efflorescence are called efforescent
For example: Washing soda No,CO, 10H,O, Glauber’s salt (No 50, 10H,O), Blue vitriol