Maharashtra Board Class 9 Science Solution Chapter 5 – Acids, Bases and Salts
Balbharati Maharashtra Board Class 9 Science Solution Chapter 5: Acids, Bases and Salts. Marathi or English Medium Students of Class 9 get here Acids, Bases and Salts full Exercise Solution.
Std |
Maharashtra Class 9 |
Subject |
Science Solution |
Chapter |
Acids, Bases and Salts |
1.) Identify the odd one out and justify.
Ans:
a) chloride, nitrate, hydride, ammonium:
Ammonium, since ammonium is the only one cation while others are the anions.
b) hydrogen chloride, sodium hydroxide, calcium oxide, ammonia:
Hydrogen chloride, since only hydrogen chloride is the acid while all the others are the bases.
c) acetic acid, carbonic acid, hydrochloric acid, nitric acid:
Acetic acid, since acetic acid is the only one organic acid while all the others are the inorganic acids.
d) ammonium chloride, sodium chloride, potassium nitrate, sodium sulphate:
Ammonium chloride, since ammonium chloride is only one acidic salt while all the others are the neutral salts.
e) sodium nitrate, sodium carbonate, sodium sulphate, sodium chloride:
Sodium chloride, since sodium chloride is the only one neutral salt.
f) calcium oxide, magnesium oxide, zinc oxide, sodium oxide:
Zinc oxide, since zinc oxide is the only one amphoteric oxide while all the others are the basic oxide.
g) crystalline blue vitriol, crystalline common salt, crystalline ferrous sulphate, crystalline sodium carbonate:
Crystalline common salt, since it doesn’t loses its property of crystallization after the heating also.
h) sodium chloride, potassium hydroxide, acetic acid, sodium acetate:
Potassium hydroxide, since potassium hydroxide is not the salt while all the others are the salts.
2.) Write down the changes that will be seen in each instance and explain the reason behind it.
a) 50ml water is added to 50ml solution of copper sulphate.
Ans:
50 ml water is added to 50 ml solution of copper sulphate is the reversible reaction. Initially in this reaction colour changes from pale blue to white colour. And if we add water again in that solution then it turns to further blue in colour.
The chemical reaction occurred here is given by,
CuSO4 + H2O -> CuSO4•H2O i.e. blue vitriol
b) Two drops of the indicator phenolphthalein were added to 10 ml solution of sodium hydroxide.
Ans:
- Phenolphthalein is the indicator which is mainly used for identifying the quantity of base in a given solution.
- When we add two drops of the indicator phenolphthalein to the 10ml solution of sodium hydroxide then that solution become pink in colour.
- This is happened because phenolphthalein is reacted with base in the solution and it has form the sodium salt of phenolphthalein which has pink colour.
c) Two or three filings of copper were added to 10ml dilute nitric acid and stirred.
Ans:
- Copper is not more reactive metal and also it can’t react with the dilute acids immediately.
- There are two chemical reactions of copper with dilute nitric acid on the basis of the nitric acid taken is concentrated or not.
- When copper reacts with dilute nitric acid then following chemical reaction occurs.
- Cu + 4HNO3 dil. -> Cu(NO3)2 + 2NO2 + 2H2O
- When copper reacts with concentrated nitric acid following chemical reaction takes place.
- 3Cu + 8HNO3 conc. -> 3Cu(NO3)2 + 2NO + 4H2O
- Concentrated nitric acid is the strong oxidising agent.
d) A litmus paper was dropped into 2ml dilute HCl. Then 2ml concentrated NaOH added to it and stirred.
Ans:
- When we dropped a litmus paper into 2ml of dilute HCl then blue litmus paper becomes red in colour only and red litmus paper remain as it is.
- Further if we have dropped same litmus paper in the 2ml of concentrated NaOH solution then red litmus paper becomes blue in colour but then no change in blue litmus paper.
- The change in colour of litmus paper is due to they dropped in acid and bases.
e) Magnesium oxide was added to dilute HCl and magnesium oxide was added to dilute NaOH.
Ans:
- We know that, in neutralisation reaction acid and base reacts with each other and forms salt and water.
- When magnesium oxide was added to dilute HCl the following neutralisation reaction occurs.
- MgO + 2HCl -> MgCl2 + H2O
- When magnesium oxide was added to dilute NaOH, it doesn’t reacts with NaOH because bases reacts with oxides of non metal and neutralisation reaction takes place.
- Since oxides of non metal are acidic in nature when they reacts with dilute NaOH neutralisation reaction takes place. Here magnesium oxide is the metal oxide which acts as the base.
f) Zinc oxide was added to dilute HCl and zinc oxide was added to dilute NaOH.
Ans:
- When zinc oxide was added to dilute HCl then acid base neutralisation reaction takes place with the formation of salt and water.
- The chemical reaction occurred is as follows:
- ZnO + 2HCl -> ZnCl2 + HCl
- When zinc oxide was added to dilute NaOH, then zincate sodium and water is formed. In this reaction heat is evolved and it occurs at 500 – 600°C temperature.
- The chemical reaction occurred is as follows.
- ZnO + 2NaOH -> Na2ZnO2 + H2O
g) Dilute HCl was added to limestone.
Ans:
Calcium carbonate is called as limestone. When dilute HCl is added to limestone the following chemical reaction takes place.
2HCl + CaCO3 -> CaCl2 + CO2 + H2O
h) Pieces of blue vitriol were heated in test tube. On cooling water was added to it.
Ans:
- Blue vitriol is having crystalline structure when it is heated in a test tube its crystalline structure get broken down and colourless powder is formed with water is expelled out.
- The water comes out is called as the crystalline water.
- When we add water to the same test tube then white powder formed is again turned into blue colour and the reaction takes place which is reversible reaction explained as follows.
- CuSO4•5H2O <–> CuSO4 + 5H2O
i) Dilute H2SO4 was taken in an electrolytic cell and electric current is passed through it.
Ans:
- When electrolysis of dilute H2SO4 takes place in an electrolytic cell then there will be evolution of gases at anode and cathode takes place.
- The gas evolved at cathode electrode is produces pop sound which tells us that there is a hydrogen gas is evolved at cathode.
- And the gas produced at anode is the oxygen.
- When the ions are attracted towards the respective electrodes there will be evolution of gases takes place at electrodes.
- And the reactions takes place at each electrode is as follows.
At cathode:
2H+ + 2e- –> H2
At anode:
4OH- – 4e- -> 2H2O + O2
3.) Classify following oxides into three types and name the types.
CaO, MgO, CO2, SO3, Na2O, ZnO, Al2O3, Fe2O3.
Ans:
Oxides are classified into three types which are as follows.
1) Acidic oxides:
SO3, CO2
2) Basic oxides:
CaO, MgO, Na2O
3) Amphoteric oxide:
ZnO, Al2O3, Fe2O3
4.) Explain by drawing the figure of electronic configuration.
a) Formation of sodium chloride from sodium and chlorine
b) Formation of magnesium chloride from magnesium and chlorine
Ans:
a)
- Na has atomic number as 11 with electronic configuration is 2,8,1.
- As there is only one Valence electron in the last shell of Na, it prefer to lose one electron in order to get stable electronic configuration.
- Thus, Na loses one electron and forms Na+.
- The atomic number of chlorine is 17 with electronic configuration is 2,8,7.
- That means it has deficiency of only one electron to get stable electronic configuration.
- Hence it receives one electron and forms Cl- ion.
- In this way, sodium loses one electron which is received by the chlorine and sodium chloride is formed with ionic bonding between them.
- The following is the reaction showing formation of sodium chloride from sodium and chlorine.
b)
- The atomic number of magnesium is 12 with electronic configuration is 2,8,2.
- That means it has , 2 Valence electron in its last shell. So Mg loses 2 electrons to get stable electronic configuration and forms Mg2+.
- The atomic number of chlorine is 17 with electronic configuration 2,8,7. That means it has deficiency of one electron. Hence it receives one electron to get stable electronic configuration and forms Cl-.
- In this way, Mg receives 2 electrons from two chlorine atoms and form MgCl2 with the formation of ionic bond between them.
- The following reaction shows the how MgCl2 is formed from Mg and Cl.
5.) Show the dissociation of following compounds on dissolving in water, with the help of chemical equation and write whether the proportion of dissociation is small or large.
Hydrochloric acid, sodium chloride, potassium hydroxide, ammonia, acetic acid, magnesium chloride, copper sulphate.
Ans:
1) Hydrochloric acid:
When hydrochloric acid is dissolved in water the following chemical reaction takes place.
HCl + H2O -> H3O+ + Cl-
Here, the proportion of dissociation is large and HCl completely dissolved in water.
2) Sodium chloride:
When sodium chloride is dissolved in water the following chemical reaction takes place.
NaCl + H2O -> Na+ + Cl-
Here, NaCl completely dissolved in water but no chemical reaction takes place due to the high polarity of water.
3) Potassium hydroxide:
When potassium hydroxide is dissolved in water the following chemical reaction takes place.
KOH + H2O -> K+ + OH-
Here, KOH on dissociation with water forms the K+ and OH- ions only.
4) Ammonia:
When ammonia is dissolved in water the following chemical reaction takes place.
NH3 + H2O -> OH- + NH4+
Here, ammonia dissolved in water readily and forms the OH- and NH4+ ions only.
5) Acetic acid:
When acetic acid is dissolved in water the following chemical reaction takes place.
CH3COOH + H2O -> CH3COO- + H3O+
Here, acetic acid dissolved in water on large scale and it forms acetate ion and hydronium ions.
6) Magnesium Chloride:
When magnesium chloride is dissolved in water the following chemical reaction takes place.
MgCl2 + H2O -> Mg2+ + Cl-
Here, on dissociation with water MgCl2 gives Magnesium and chloride ions only.
7) Copper sulphate:
When copper sulphate is dissolved in water the following chemical reaction takes place.
CuSO4 + H2O -> Cu2+ + SO42-
Here, copper sulphate on dissociation with water gives copper and sulphate ions with the release of energy.
6.) Write down the concentration of each of the following solution in g/L and mole/L.
a) 7.3g HCl in 100ml solution
b) 2g NaOH in 50ml solution
c) 3g CH3COOH in 100ml solution
d) 4.9g H2SO4 in 200ml solution
Ans:
a) 7.3g HCl in 100ml solution:
We know that, the concentration of HCl in g/L is given by,
Conc. Of HCl = mass of solute in g/volume of HCl in L
= 7.3*1000/100
= 73g/L
Molecular mass of HCl = 1+ 35.5= 36.5
The molarity of HCl is given by,
Molarity= mass of solute in moles/ volume of solution in L
= 7.3*1000/36.5*100
= 2mole/L
Thus, 7.3g of HCl in 100ml solution has concentration 73g/L and 2mole/L.
b) 2 g NaOH in 50ml solution:
We know that, the concentration of NaOH in g/L is given by,
Conc. Of NaOH= mass of solute in g/ volume of NaOH in L
= 2*1000/50
= 40 g/L
Molecular mass of NaOH= 23 + 1 + 16= 40
The molarity of NaOH is given by,
Molarity= mass of solute in moles/ volume of solution in L
= 2*1000/40*50
= 1mol/L
Thus, 2 g of NaOH in 50ml solution has concentration 40g/L and 1mole/L.
c) 3 g of CH3COOH in 100ml solution:
We know that, the concentration of CH3COOH in g/L is given by,
Conc. Of CH3COOH= mass of solute in g/ volume of CH3COOH in L
= 3*1000/100
= 30g/L
Molecular mass of CH3COOH= 24 + 32 + 4 = 60
The molarity of CH3COOH is given by,
Molarity= mass of solute in moles/ volume of solution in L
= 3*1000/60*100
=0.5mole/L
Thus, 3g of CH3COOH in 100ml of solution has concentration 30g/L and 0.5mole/L.
d) 4.9 g of H2SO4 in 200ml solution:
We know that, the concentration of H2SO4 in g/L is given by,
Conc. Of H2SO4 = mass of solute in g/ volume of H2SO4 in L
= 4.9*1000/200
= 24.5g/L
Molecular mass of H2SO4 = 98
Molarity of H2SO4 is given by,
Molarity= mass of solute in moles/ volume of solution in L
= 4.9*1000/98*200
= 1mol/L
Thus, 4.9 g of H2SO4 in 200ml solution has concentration 24.5g/L and 1mol/L.
7.) Answer the following questions.
a) Classify the acids according to their basicity and give one example of each type.
Ans:
Basicity is the number of H+ ions which are present in the one molecule of an acid.
On the basis of basicity of acids, acids are classified into three types:
a) Monobasic acids
b) Dibasic acids
c) Tribasic acids
a) Monobasic acids:
Monobasic acids are those acids which on ionisation gives only one H+ ion.
For example: HCl, HNO3
b) Dibasic acids:
Dibasic acids are those acids which on ionisation gives two H+ ions.
For example: H2SO4, H2CO3
c) Tribasic acids
Tribasic acids are those acids which on ionisation gives three H+ ions.
For example: H3PO3, H3PO4.
b) What is meant by neuralization? Give two examples from everyday life of the neutralisation reaction.
Ans:
When acid and base reacts with each other then salt and water is formed this reaction is called as neutralisation reaction.
For example:
HCl + NaOH ->NaCl + H2O
In this reaction, HCl is the acid and NaOH is the base which on reacting together forms the salt NaCl and water.
The daily life examples of neutralisation reaction are as follows:
1)
- When we eat sugary foods, some of the particles of that sweet food remains in our tooth. The bacteria from the tooth breaks that particles and forms the acid.
- Due to the formation of these acids the decay of tooth will takes place. So to lower the quantity of acid in our tooth we have to brush the tooth after eating.
- The toothpaste contains base which reacts with acid in our tooth and neutralises it.
- In this way, we can protect our teeth.
2)
- We know that, plants grow in soil with well development and growth only when the pH of soil is neutral i.e. 7.
- If the soil nature is too acidic or too basic then there will be no well growth of plants occurs.
- When the soil is too acidic then it is neutralized by using slaked lime or chalk.
- When the soil is too basic then it is neutralized by adding decaying organic matters which are acidic in nature.
c) Explain what is mean by electrolysis of water. Write the electrode reaction and explain them.
Ans:
- When electric current is passed through the water then it’s decomposition into hydrogen and oxygen gas takes place called as electrolysis.
- At cathode, reduction reaction takes place while at anode oxidation reaction takes place.
- At cathode, the H+ ions from water takes electrons and forms the hydrogen gas which is shown in following reaction.
2H+ + 2e- -> H2
- At anode oxidation reaction takes place, water loses electrons and forms oxygen gas with H+ ions which is shown in the following reaction.
2H2O -> O2 + 4H+ + 4e-
- We can write the overall reaction as follows.
2H2O -> 2H2 + O2
- In this way, during the electrolysis of pure water oxygen and hydrogen gas are evolved. The volume of hydrogen gas is twice the volume oxygen gas evolved.
8.) Write the chemical equations for the following activities.
a) NaOH solution was added to HCl solution.
b) Zinc dust was added to dilute H2SO4.
c) Dilute nitric acid was added to calcium oxide.
d) Carbon dioxide gas was passed through KOH solution.
e) Dilute HCl was poured on baking soda.
Ans:
a) NaOH solution was added to HCl then neutralisation reaction takes place which is given below.
NaOH + HCl ->NaCl + H2O
b) When zinc dust was added to dilute H2SO4 zinc sulphate is formed with the evolution of hydrogen gas.
The reaction occurred is as follows.
Zn + Dil. H2SO4 -> ZnSO4 + H2
c) When dilute nitric acid was added to calcium oxide the reaction occurred is as follows.
CaO + Dil. 2HNO3 -> Ca(NO3)2 + H2O
d) When carbon dioxide gas was passed through KOH solution then the reaction occurred is as follows.
2KOH + CO2 -> K2CO3 + H2O
e) when dilute HCl was poured on baking soda the reaction occurred is as follows.
HCl + NaHCO3 ->NaCl + CO2 + H2O
9.) State the difference.
a) Acids and bases
b) cation and anion
c) negative electrode and positive electrode
Ans:
a) Acids and bases:
Acids:
- Acids are those which are on dissolution gives H+ ions.
- Acids are those which lose the electrons while forming H+ ion.
- The strength of acids depends on the concentration of H+ ion.
- Acids are having pH less than 7 and they are sour to taste.
- In acids blue litmus paper turns into red.
For example: HCl
Bases:
- Bases are those which on dissociation in water accept the H+ ions.
- Bases always try to receive protons.
- The strength of base is depends on the concentration of OH- ions.
- The pH of base is greater than 7 and they are bitter to taste.
- In bases red litmus paper turns to blue.
For example: NaOH.
b) cation and anion:
Cations:
- Cations are the positively charged species.
- Cations are formed when loss of electrons is takes place.
- In the process of electrolysis, the cations which are positive in nature moves towards the cathode electrode.
- Cations are smaller in size as compared to their parent atom.
For example: Ca2+, Mg2+, Na+.
Anions:
- Anions are the negatively charged species.
- Anions are formed when electrons are received from the non metals.
- As anions are negative in nature they moves towards the anode electrode during the process of electrolysis.
- The size of anion is small or greater than the its parent atom.
For example: Cl-, OH-, Br-.
c) negative electrode and positive electrode:
Negative electrode:
- It is the negative pole of the electrochemical cell.
- It connects the negative terminal of battery with help of wire.
- The negative electrode is called as cathode.
- As cathode is negative electrode hence positive charged cations moves towards the cathode.
- Electrons are deposited on the negative electrode cathode.
Positive electrode:
- It is the positive pole of the electrochemical cell.
- It is connected to the positive terminal of the battery with the help of wire.
- Positive electrode is also called as anode.
- As the anode is positive electrode the anions are attracted towards the anode.
- Anode donates the electron by oxidation reaction.
10.) Classify the aqueous solution of the following substances according to their pH into three groups: 7, more than 7 and less than 7.
Common salt, sodium acetate, Hydrochloric acid, carbon dioxide, potassium bromide, calcium hydroxide, ammonium chloride, vinegar, sodium carbonate, ammonia, sulphur dioxide.
Ans:
Following are the substances which are having pH equal to 7:
Solution of common salt, solution of potassium bromide.
Following are the substances which are having pH less than 7:
Hydrochloric acid, carbon dioxide, ammonium chloride, vinegar, sulphur dioxide.
Following are the substances which are having pH greater than 7:
Sodium acetate, calcium hydroxide, sodium carbonate, ammonia.