Rajasthan Board RBSE Class 10 Science Important Questions Chapter 2 Acids, Bases and Salts Important Questions and Answers.
RBSE Class 10 Science Chapter 2 Important Questions Acids, Bases and Salts
Objective Type Questions:
Question 1.
Which acid is produced by our stomach?
(a) H2SO4
(b) HNO3
(c) NaOH
(d) HCl
Answer:
(d) HCl
Question 2.
The nature of toothpaste used for the cleaning of teeth is:
(a) Basic
(b) Acidic
(c) Neutral
(d) Corrosive
Answer:
(a) Basic
Question 3.
Which of the following is used for disinfecting drinking water to make it free of germs?
(a) Baking soda
(b) Bleaching powder
(c) Washing soda
(d) None of the above
Answer:
(b) Bleaching powder
Question 4.
The pH value of distilled water is:
(a) 9
(b) 7
(c) 5
(d) 3
Answer:
(b) 7
Question 5.
The nature of our blood is:
(a) Acidic
(b) Basic
(c) Neutral
(d) Slightly acidic and slightly basic
Answer:
(b) Basic
Question 6.
The nature of non-metal oxide is:
(a) Basic
(b) Acidic
(c) Neutral
(d) Inert
Answer:
(b) Acidic
Question 7.
When concentrated H2SO4 is added in water:
(a) Heat is absorbed
(b) Heat is evolved
(c) No change
(d) Solution become viscous.
Answer:
(b) Heat is evolved
Question 8.
The compound formed on heating of baking soda is:
(a) NaNO3
(b) Na2CO3
(c) NH4Cl
(d) NaHCO3
Answer:
(b) Na2CO3
Question 9.
Which of the following gives hydrogen gas by the reaction with dilute sulphuric acid?
(a) Zn
(b) Mg
(c) Fe
(d) All of the above
Answer:
(d) All of the above
Very Short Answer Type Questions:
Question 1.
Write two major components of baking powder ?
Answer:
- NaCl (sodium chloride).
- CO2, NH3.
Question 2.
Name the acidic oxides that cause acid rain.
Answer:
- Sulphuric acid (H2SO4).
- Nitric acid (HNO3).
Question 3.
Name two synthetic indicators.
Answer:
Phenolphthalein and methyl orange are the examples of synthetic indicators.
Question 4.
Which one has high pH value:
(i) Blood or distilled water?
(ii) Gastric juice or lemon juice?
Answer:
- Blood
- Lemon juice.
Question 5.
What is the value of pH for a neutral solution?
Answer:
For a neutral solution value of pH is 7.
Question 6.
Write the name of the acid, secreted from sting of ant.
Answer:
Methanoic acid.
Question 7.
Write the names of two compounds which have hydrogen but they are not acids and electricity is not passed in the solution of these.
Answer:
Alcohol (C2H5OH) and glucose (C6H12O6).
Question 8.
The method of measurement of hydrogen ion concentration is given by which scientist?
Answer:
Sorenson.
Question 9.
What is the pH of lemon juice?
Answer:
Tomato juice is acidic so pH of this is 4.0 – 4.4.
Question 10.
What is the pH of ‘Milk of Magnesia’?
Answer:
‘Milk of Magnesia’ has a pH value of 10.
Question 11.
Explain the usefulness of ‘Milk of Magnesia’.
Answer:
Milk of Magnesia (Magnesium hydroxide) is a weak base and is used as antacid to neutralise the excess amount of acid.
Question 12.
Write the equation for the reaction of Zn with NaOH solution in which H2 gas is formed.
Answer:
Question 13.
Write the nature of metal oxides. Give two examples.
Answer:
Metal oxides are generally basic in nature. Example CaO, MgO.
Question 14.
Write the two examples of strong acids and strong bases each.
Answer:
Strong acid:
HCl (Hydrochloric acid) and H2SO4 (Sulphuric acid).
Strong Base:
NaOH (Sodium Hydroxide) and KOH (Potassium hydroxide).
Question 15.
Write the two examples of weak acids and weak bases each.
Answer:
Weak acid:
CH3COOH and HCN
Weak Base:
NH4OH and Mg(OH)2
Question 16.
What are universal indicators?
Answer:
Universal indicators are mixture of different indicators. These represents the different concentrations of H+ ion in a solution in different colours.
Question 17.
What is the pH of gastric juice?
Answer:
The pH of gastric juice is approxi-mately 1.2.
Question 18.
Which acid is present in tomato?
Answer:
Oxalic acid is present in tomato.
Question 19.
Write the four salts of sodium group.
Answer:
Sodium sulphate (Na2SO4), Sodium chloride (NaCl), Sodium nitrate (NaNO3) and sodium carbonate (Na2CO3).
Question 20.
The aqueous solution of sodium acetate is basic, why?
Answer:
Sodium acetate (CH3COONa) is a salt formed by weak acid (CH3COOH) and strong base (NaOH). So the aqueous solution of this is basic.
Question 21.
Which gas is given off at cathode and anode when electricity is passed in the aqueous solution of sodium chloride?
Answer:
When electricity is passed in the aqueous solution of sodium chloride then H2 gas is given off at cathode and chlorine gas at anode.
Question 22.
Write the equation used in the manufacture of baking soda.
Answer:
Question 23.
What is the specific name of CUSO4.5H2O ?
Answer:
The specific name of CuSO4.5H2O is Blue vitreol.
Question 24.
How many water molecules are attached with Na2CO3 crystal?
Answer:
10 water molecules are attached with the crystal of Na2CO3.(Na2CO3. 10H2O).
Question25.
What is the chemical name of Gypsum?
Answer:
Chemical name of Gypsum (CaSO4.2H2O) is calcium sulphate dihydrate.
Question26.
Write the different forms of calcium carbonate (CaCO3).
Answer:
Limestone, chalk and marble are different forms of calcium carbonate.
Question 27.
Which daily useful compound is used to give relief from the pain and irritation caused by bee-sting?
Answer:
Use of a mild base like ‘baking soda’ on the stung area gives relief.
Question 28.
Which acid is present in lemon juice?
Answer:
Citric acid is present in lemon juice.
Question 29.
Write the chemical formulae of bleaching powder.
Answer:
CaOCl2.
Question 30.
The aqueous solution of washing soda is acidic or basic?
Answer:
Basic
Question 31.
Name some natural materials which indicate the presence of acid or base in a solution.
Answer:
There are many 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.
Question 32.
In the pH scale what does P indicates?
Answer:
In the pH scale p indicates ‘Potenz’ which means power.
Question 33.
What is dilution?
Answer:
When water is added in acid or base then H2SO4 concentration per unit volume decreases. This process is called dilution.
Question 34.
What is the meaning of water of crystallisation?
Answer:
Definite number of water molecules present in per unit formula of salt is called water of crystallisation.
Short Answer Type Questions:
Question 1.
Which among the following is a strong acid and strong base ?
(i) Acetic acid or hydrochloric acid.
(ii) Sodium hydroxide or Calcium hydroxide.
Answer:
(i) Strong acid: Hydrochloric acid (HCl)
(ii) Strong base: Sodium hydroxide (NaOH).
Question 2.
What is pH Scale ? Explain that pH change of the mouth is a cause of tooth decay.
Answer:
pH Scale:
A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. On the pH scale one can measure the pH from O (very acidic) to 14 (very alkaline). The pH of a neutral solution is 7. Values less than 7 on the pH scale represent an acidic solution and if the pH value is more than 7, the solution will be alkaline in nature. Tooth decay starts when the pH of the mouth is lower than 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating, this reduces the pH of the mouth below 5.5 which causes tooth decay.
Question 3.
Zinc produces gas X on reaction with sulphuric acid:
(i) Name the gas X.
(ii) Write the equation of the reaction.
(iii) How will you identify gas X?
Answer:
(i) Hydrogen gas is produced by the reaction of zinc with sulphuric acid.
(iii) For the identification of the gas burning candle is brought near the mouth of the test tube. This gas bums with Blue flame and POP sound.
Question 4.
(a) Give the name of the gas evolved when sodium hydroxide reacts with zinc metal. Write the equation also.
(b) Which is used in the following:
(i) To make drinking water free from germs.
(ii) For making tasty crispy Pakoras in kitchen.
(iii) To remove permanent hardness of water.
(iv) For making toys and decorative materials.
Answer:
(a) Hydrogen gas is liberated by the reaction of sodium hydroxide with Zinc metal.
(b) (i) Bleaching powder
(ii) Baking soda
(iii) Washing soda
(iv) Plaster of Paris.
Question 5.
(i) Strong acid | (a) turmeric |
(ii) Weak acid | (b) NH4Cl |
(iii) Antacid | (c) Na2C03 |
(iv) Strong base | (d) Methyl orange |
(v) Weak base | (e) CH3COOH |
(vi) Neutral salt | (f) H2SO4 |
(vii) Acidic salt | (g) NH4OH |
(viii) Basic salt | (h) milk of magnesia |
(ix) Natural indicator | (i) NaOH |
(x) Synthetic indicator | (j) NaCl |
Answer:
(i) Strong acid | (f) H2SO4 |
(ii) Weak acid | (e) CH3COOH |
(iii) Antacid | (h) milk of magnesia |
(iv) Strong base | (i) NaOH |
(v) Weak base | (g) NH4OH |
(vi) Neutral salt | (c) Na2C03 |
(vii) Acidic salt | (b) NH4Cl |
(viii) Basic salt | (j) NaCl |
(ix) Natural indicator | (a) turmeric |
(x) Synthetic indicator | (d) Methyl orange |
Question 6.
Litmus is natural indicator or artificial? The spot of vegetable on white cloth becomes red brown with soap. Why?
Answer:
Litmus is a natural indicator. The spot of vegetable on white cloth becomes red brown with soap because the turmeric present in vegetable gives red brown colour by the reaction with basic soap. Turmeric is also a natural indicator like litmus.
Question 7.
What causes acidic properties in acids and basic properties in bases ?
Answer:
Acids produce hydrogen ions, H+(aq), in solution, which are responsible for their acidic properties whereas base produce hydroxide ion, OH (aq) in solution due to which their properties are basic.
Question 8.
Select the Acid and Base out of Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3), Acetic acid (CH3COOH), Sodium hydroxide (NaOH), Calcium hydroxide [Ca(OH)2], Potassium hydroxide (KOH), Magnesium hydroxide [Mg(OH)2] and Ammonium hydroxide (NH4OH), present in science laboratory. Out of these which will turn the solution of phenolphthalein to pink and which will turn the colour of methyl orange indicator yellow to red?
Answer:
From the above compounds acids and bases are as follows:
Acids:
HCl, H2SO4, HNO3, CH3COOH
Bases:
NaOH, Ca(OH)2, KOH, Mg(OH)2, NH4OH
Acids turns blue litmus into red and yellow colour of methyl orange, on the contrary.
Bases turns red litmus into blue and phenolphthalein solution to pink.
Question 9.
How the reaction of metals occurs with acid and base. Is this occurs with all metals and all acids. Explain with examples.
Answer:
Metals gives hydrogen gas by the reaction with acids and forms a compound by the combination of remaining part of acid, which is called salt. The reaction of metal with acid can be represented as:
Acid + Metal → Salt + Hydrogen gas
Mg(s) + H2SO4(aq) → MgSO4 (aq) + H2(g)
Only active metals gives H2 by the reaction with hydrogen acids.
Some metals also reacts with bases and form salts, like Zn, Al, etc.
But these reactions are not possible with all metals.
Question 10.
What is antacid ? Give example.
Answer:
The bases that are used to neutralize the excess amount of acid in the stomach are called antacids. Examples: bicarbonates of aluminium, calcium, magnesium and sodium.
Question 11.
Which gas is formed by the reaction of metal carbonate (Na,CO2) and metal hydrogen carbonate (NaHCO3) with dilute HCl and what happens when this gas is passed through lime water? Explain with equations.
Answer:
CO2 gas is formed by the reaction of metal carbonate and metal hydrogen carbonate with dilute HCl and salt and water is formed.
Na2CO3(s) + 2HCl(aq) → 2NaCl(aq)+ H3O(g) + CO2(g)
NaHO3(s) + HCl(aq) → NaCl(aq) + H2O(Z) + CO2(g)
When the CO2 gas is passed through lime water, white precipitate of CaCO3 is formed and on passing excess carbon dioxide the solution again becomes colourless due to the formation of calcium hydrogen carbonate.
Question 12.
Metal oxides are acidic or basic? What happens when these are treated with Acid? Explain with examples.
Answer:
Metal oxides are generally basic in nature when these are treated with acids then forms salt and water.
Example: Metal oxide + Acid → Salt + Water
Question 13.
CO2 which is the oxide of carbon (non-metal) reacts with base [Ca(OH),] and forms salt and water. What does it prove?
Answer:
CO2 forms salt and water by the reaction with base [Ca(OH)2], It proves acidic nature of CO2. This is similar to reaction between acid and base. So non¬metal oxides are acidic in nature.
Question 14.
If a member of your family is suffering from acidity due to excessive eating, what treatment would you recommend ?
Answer:
Our stomach produces hydrochloric add (HCl). It helps in digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain, irritation and burning is experienced in stomach. This is called acidity. To relieve this pain, bases such as antacid are used which neutralize the excessive amount of acid. Weak bases such as magnesium hydroxide (milk of magnesia) are used for this.
Question 15.
Define acid and base. Give the examples also.
Answer:
Acids are the substances which give H+ or H3O+. In aqueous solution but H+ does not remain free and form H2O+ by the reaction with H2O. Acidic property of acids is due to H+.
example:
Bases are the substances which give OH (Hydroxide) ion in aqueous solution. All the Bases are not soluble in water. The base which is soluble in water is called alkali. These are soapy, corrosive and bitter in taste.
Example: NaOH, KOH etc.
Question 16.
What is pH scale? How the acidic or basic nature of a solution is determined by this? Explain.
Answer:
pH scale: A scale for measuring hydrogen ion concentration of a solution is called pH scale. The p in pH stands for ‘potenz’ in German, meaning power. On the pH scale we can measure pH from 0 (very acidic) to 14 (very alkaline). Generally pH should be thought of simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value.
The pH of a neutral solution is 7. Values less than 7. on the pH scale represent an acidic solution. As the pH value increases from 7 to 14, it represents an increase in OH ion concentration in the solution, that is, increase in the strength of alkali.
Question 17.
On which the strength of acids and bases depends? What is meant by strong acid, weak acid and strong base, weak base ?
Answer:
The strength of acids and bases depends on number of H+ ions and OH ions produced in the solution (water).
Strong and Weak acid:
The acids which give rise to more H+ ions in aqueous solution are said to be strong acids like hydrochloric acid while acids that give less H+ ions are said to be weak acids like acetic acid (CH3COOH).
Strong and Weak Base:
The bases which give rise to more OH ions in aqueous solution are said to be strong bases like NaOH, KOH etc. While bases that give less Off ions are said to be weak bases like NH4OH, Ca(OH)2 etc.
Question 18.
Write the list of some acids obtained from natural sources.
Answer:
Some naturally occuring acids are as follows:
Acid obtained Acetic acid Citric acid Tartaric acid Oxalic acid Lactic acid
Natural source | Acid Obtained |
1. Vinegar | Acetic Acid |
2. Orange | Critic Acid |
3. Tamarind | Tartaric Acid |
4. Tomato | Oxlic Acid |
5. Sour milk (curd) | Latic Acid |
6. Lemon | Critic Acid |
7. Ant sting | Methanoic Acid |
8. Nettle sting | Methanoic Acid |
Question 19.
The pH of solution of different salts is different. Why? What will be pH of solution of following salts and also name the acid and base by which they are formed? Sodium chloride, Potassium nitrate, Zinc sulphate, Copper sulphate, Sodium acetate and Sodium Hydrogen carbonate.
Answer:
The pH of solution of different salts is different because they form acids and bases of different strength by the reaction with water. The pH of solution of salt formed with strong acid and strong base is 7. While the pH of solution of salt formed with strong acid and weak base is less than 7 and the pH of the solution of salt formed with strong base and weak acid is more than 7.
The pH value, nature of solution, acid and base used in the formation of given salts are as follows:
Salt | Acid Used | Nature of Sol. | |
1. Sodium chloride (NaCl) | HCl | 7 | Neutral |
2. Potassium nitrate (KNO3) | HNO3 | 7 | Neutral |
3. Zinc sulphate (ZnSO4) | H2SO4 | less than 7 | Acidic |
4. Copper sulphate (CuSO4) | H2SO4 | less than 7 | Acidic |
5. Sodium acetate (CH3COONa) | CH3COOH | more than 7 | Basic |
6. Sodium Hydrogen carbonate (NaHCO3) | H2CO3 | Basic |
Question 20.
Explain the cause of tooth decay and write two ways to prevent it.
Answer:
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. Bacteria present in the mouth produce acids by the degradation of sugar and food particles remaining in the mouth after eating.
Ways to prevent it:
(i) The best way to prevent it into clean the mouth after eating food.
(ii) Using toothpaste, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.
Question 21.
Write the four salts of chloride family, nitrate family and sulphate family each.
Answer:
1. Salts of Chloride family:
- NaCl, Sodium chloride
- KCl, Potassium chloride
- MgCl2, Magnesium chloride
- NH4Cl, Ammonium chloride.
2. Salts of Nitrate family:
- KNO3, Potassium Nitrate
- NaNO3, Sodium Nitrate
- Ca (NO2)2, Calcium Nitrate
- NH4NO3, Ammonium Nitrate.
3. Salts of Sulphate family:
- K2SO4, Potassium sulphate
- NaSO2 sodium sulphate,
- MgSO4, Magnesium sulphate
- CuSO4, Copper sulphate.
Qustion 22.
What is Chlor – Alkali Process? Explain with examples and write the uses of the products formed by this also.
Answer:
Chlor – Alkali Process:
When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. This process is called chlor-alkali process because of the products formed chlor for chlorine and alkali for sodium hydroxide.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g) Chlorine gas is given off at the anode and hydrogen gas at the cathode. Sodium hydroxide solution is also formed near the cathode. The three-products H2, Cl2 and NaOH produced in this process are’ very useful. H2 gas is used as fuel, margarine and in the formation of ammonia for fertilizers.
Cl, gas is used in the cleaning of water and in the formation of P.V.C. disinfectant, CFC and pesticides. NaOH is used for de-greasing of metals and formation of artificial fibres, soaps and detergents. HCl (Hydrochloric acid) formed by the reaction of H2 and Cl2is used for cleaning of steel, and in the formation of ammonium chloride, medicines and cosmetics. Bleaching powder is formed by the reaction of NaOH and Cl2 which is used in the bleaching of fabric etc.
Question 23.
What is water of crystallisation? Give the two examples of compounds having water of crystallisation. What happens when these compounds are heated ?
Answer:
Water of crystallisation: The definite number of water molecules present in each formula unit of a salt in its crystalline form is called water of crystallisation.
Example:
1. CuSO4.5H2O (Crystalline copper sulphate Blue colour) When it is heated, water molecules are removed and it becomes colourless (white). It becomes blue again when water is added in it.
2. Na2CO3. 10H2O (Washing soda) Water molecules are also removed from it when it is heated.
Na2CO3.10H2O → Na2CO3 + 10H2O
Question 24.
What is Plaster of Paris? How it is prepared and what’ are the uses of it ?
Or
Write the chemical formula and chemical reaction of Plaster of Paris with water.
Answer:
CaSO4 10H2O is called Plaster of Paris.
Formation:
On heating gypsum at 373 K, it loses \Vater molecules and forms calcium sulphate hemihydrate (caSO4 10H2O). This is called Plaster of Paris. It is used as plaster for supporting fractured bones in the right position. Plaster of Paris is a white powder and on mixing with water, it changes to gypsum once again giving a hard solid substance.
In the Plaster of Paris only half water molecule is shown to be attached as water of crystallisation. So, two formula units of CaSO4 share one molecule of water in it.
Other uses:
Plaster of Paris is used for making toys, materials for decoration and for making surfaces smooth.
Question 25.
Write any two differences between Acid and Base.
Answer:
Acid | Base |
1. These are sour in taste. | 1. These are bitter in taste. |
2. These change the colour of blue litmus to red. | 2. These change the colour of red litmus to blue. |
Question 26.
Why calcium sulphate hemi-hydrate is called the ‘Plaster of Paris’ ?
Answer:
In ancient times, a large amount of calcium sulphate hemihydrate was produced from gypsum near Paris, hence it is also known as‘Plaster of Paris’.
Question 27.
Write the formula and two uses of Bleaching Powder.
Answer:
The formula of Bleaching Powder is CaOCl2.
Uses:
- In the form of bleaching agent.
- In the purification of drinking water.
Question 28.
Write the chemical formula and two uses of washing soda.
Answer:
The chemical formula of washing soda is Na2CO3.10H2O.
Uses:
- For the removal of permanent hardness of water.
- In the manufacture of sodium compound like borax.
Quistion 29.
The chemical reaction between an acid and a base is called neutralisation reaction, why? Give one example.
Answer:
Salt and water are formed by the chemical reaction between acid and base means both neutrals each other. So the reaction between acid and base is called neutralisation reaction.
Example:
Question 30.
What is Litmus? Explain.
Answer:
Litmus: This is a natural indicator which is extracted from lichen, a plant belonging to the division Thallophyta. When the litmus solution is neither acidic nor basic then its colour is purple. This is generally used as acid base indicators.
Question 31.
What is olfactory indicators?
Answer:
Olfactory indicators: The subs-tances whose odour changes in acidic or basic media, these are called olfactory indicators. Small pieces of onion, clove oil and vanila essence are used as olfactory indicators.
Question 32.
Write about Nettle.
Answer:
Nettle is a herbaceous plant which grows in the wild. Its leaves have stinging hair which cause pain like stings when touched accidentally. This is due to the methanoic acid secreted by them. A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows beside the nettle in the wild. As the dock plant juice is basic, this cancel the effect of acid which gives relief in the pain.
Question 33.
Write the scale which is used to determine the Hydrogen ion concen-tration. Write the reason of acid rain and two bad effects of it.
Answer:
1. The scale which is used to determine the hydrogen ion concentration is called pH scale.
2. Acid rain: When the pH of rain water becomes less than 5.6 then it is called acid rain.
Bad Effects:
1. When the water of acid rain flows into river it lowers the pH of river water. So the survival of aquatic life in such river becomes difficult.
2. Acid rain may cause skin disease by the contact of it.
Question 34.
What is ‘rock salt’ ? How it is different from common salt ?
Answer:
Deposits of solid salt are found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt. Common salt (sodium chloride) has no impurities so they are in the form of white crystals whereas impurities are found in rock salt so they are brown in colour.
Essay Type Questions:
Question 1.
Give the preparation method and uses of Bleaching powder (CaOCl2), Baking soda (NaHCO3) and Washing soda (Na2CO3.10H2O).
Answer:
1. Bleaching Powder:
Bleaching o powder is produced by the action of chlorine on dry slaked lime [Ca(OH)2], Bleaching powder is represented as CaOCl2 though the actual composition is quite complex.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Uses of Bleaching Powder:
Bleaching powder is used:
(i) for bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories and for bleaching washed clothes in laundry.
(ii) as an oxidising agent in many chemical industries and.
(iii) for disinfecting drinking water to make it free of germs.
2. Baking Soda (NaHCO3):
NaHCO3 is produced by the reaction NH3 and CO2 with NaCl.
NaHCO3 is called sodium hydrogen carbonate. It is a mild non-corrosive base. The following reaction takes place when it is heated during cooking.
Uses of Baking Soda (NaHCO3):
(i) For making baking powder, which is a mixture of baking soda (sodium hydrogen carbonate) and tartaric acid. When baking powder is heated or mixed in water, the following reaction takes place:
NaHCO3 + H+ → CO2 + H2O + Sodium salt of acid (from any acid) Carbon dioxide produced during the reaction causes bread or cake to rise making them soft and spongy.
(ii) Sodium hydrogen carbonate 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.
3. Washing Soda (Na2CO2 10H2O):
It is obtained from sodium chloride. Sodium carbonate can be obtained by heating baking soda recrystallisation of sodium carbonate gives washing soda. It is also a basic salt.
Na2CO3 + 10H2O → Na2CO2 10H2O (Sodium carbonate)
Uses of Washing Soda:
- Sodium carbonate (washing soda) is used in glass, soap and paper industries.
- It is used in the manufacture of borax (Na2B4O7).
- Sodium carbonate can be used as a cleaning agent for domestic purposes.
- It is used for removing permanent hardness of water.
Question 2.
Describe the importance of pH in everyday life.
Answer:
Importance of pH in everyday life A scale for measuring hydrogen ion concentration in a solution called pH scale has been developed. The p in pH stands for ‘potenz’ meaning power. With the pH scale we can measure pH from 0 (very acidic) to 14 (very alkaline). The importance of pH in our everyday life is as follows:
(i) Plants and animals are pH sensitive:
Our body works within the pH range of 7.0 to 7.8. Living organisms can survive only in a definite range of pH. When pH of rain water is less than 5.6, it is called acid rain. When water of acid rain flows into the river it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.
(ii) Importance in healthy growth of plants:
Plants require a specific pH range for their healthy growth. So, pH of soil from various places is determined and then it is treated accordingly. When the soil is more acidic than lime is mixed in it and when it is basic then a acidic substance is mixed to maintain proper pH.
(iii) Importance in digestive system:
pH is also important in our digestive system. Our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain and irritation in stomach. To get rid of this pain, bases called antacids are used. These antacids neutralise the excess acid Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose.
(iv) Tooth decay due to change in pH:
Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up 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. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. To prevent this mouth should be cleaned after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.
(v) Self-defence:
by chemicals produced by animals and plants Bee-sting leaves an acid which causes pain and irritation. Use of a mild base like baking soda on the stung area gives relief. Stinging hair of nettle leaves inject methanoic acid causing burning pain. A traditional remedy is, rubbing the area with the leaf of dock plant.
Question 3.
With the help of a labelled diagram, show how do metal carbonates and metal hydrogen carbonates react with acids and also write the chemical equation of the reaction.
Answer:
Chemical equation of the reaction:
(i) NaCO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO(g)
(ii) NaHCO3(s) + HCl(aq) → NaCl(aq) + H2O(l) + CO2(g)
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