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Science [5 marks Questions]

Acids, Bases and Salts · CBSE STD 10 (CBSE - English Medium). 19 questions.

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Question 15 Marks
  1. Complete and balance the following chemical equations:
  1. $\text{Al}_2\text{O}_3+\text{HCl}\xrightarrow{ \ \ \ \ \ \ \ \ \ \ \ \ }$
  2. $\text{K}_2\text{O}+\text{H}_2\text{O}\xrightarrow{ \ \ \ \ \ \ \ \ \ \ \ \ }$
  3. $\text{Fe}+\text{H}_2\text{O}\xrightarrow{ \ \ \ \ \ \ \ \ \ \ \ \ }$
  1. An element ‘X’ displaces iron from the aqueous solution of iron sulphate. List your observations if the element ‘X’ is treated with the aqueous solutions of copper sulphate, zinc sulphate and silver nitrate. Based on the observations arrange X, Zn, Cu and Ag in increasing order of their reactivities.
Answer
  1.  
  1. $\text{Al}_2\text{O}_3+6\text{HCl}\rightarrow2\text{AlCl}_3+3\text{H}_2\text{O}$
  2. $\text{K}_2\text{O}+\text{H}_2\text{O}\rightarrow2\text{KOH}$
  3. $3\text{Fe}+4\text{H}_2\text{O}\rightarrow\text{Fe}_3\text{O}_4+4\text{H}_2$
  1. $\text{X}+\text{CuSO}_4\rightarrow$Displacement reaction
$\text{X}+\text{ZnSO}_4\rightarrow$Displacement reaction
$\text{X}+\text{AgNO}_3\rightarrow$Displacement reaction
$\text{X}>\text{Zn}>\text{Cu}>\text{Ag}$
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Question 25 Marks
  1. A $6 \Omega$ resistance wire is doubled on itself. Calculate the new resistance of the wire.
  2. Three $2 \Omega$ resistors A, B and C are connected in such a way that the total resistance of the combination is $3\Omega.$ Show the arrangement of the three resistors and justify your answer.
Answer
  1. In this case: Length L becomes $\frac{1}{2}$ then Area of cross section A become 2A
$\text{R} = \rho \frac{\text{L}}{\text{A}} = 6\Omega$
$\text{R}' = \rho \frac{\text{L/2}}{2\text{A}}$
$\text{R}' = \frac{1}{4}\rho\frac{\text{L}}{\text{A}}$
$\text{R}' = \frac{1}{4} \times6$
$\text{R}' = \frac{3}{2} \Omega$
  1. No of resistors = 3
Each resistor has resistance= $2\Omega$
In this arrangement where total resistance is $3\Omega$
  1. Resistor A of is connected in series with a parallel combination of the resistors B $2\Omega$ and C $3\Omega$.
  2. Arrangement:
  1. Total resistance,
$\text{(R)} = 2\Omega + \frac{2\Omega\times2\Omega}{2\Omega + 2\Omega}$
$\text{R} = 2\Omega + \frac{4\Omega}{4\Omega}$
$\text{R} = 2\Omega + 1\Omega$
$\text{R} = 3\Omega$
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Question 35 Marks
  1. Name the following:
  1. Metal that can be cut by knife.
  2. Lustrous non-metal.
  3. Metal that exists in liquid state at room temperature.
  4. Most malleable and ductile metal.
  5. Metal that is best conductor of electricity.
  6. Non-metal that can exist in different forms.
  1. How are alloys better than metals? Give composition of solder and amalgam.
Answer
  1.  
  1. Sodium (Na)/ Potassium (K)
  2. Iodine (I)
  3. Mercury (Hg)
  4. Gold (Au)
  5. Silver/ Copper
  6. Carbon/ Sulphur/ Phosphorous
  1. They are generally stronger/ have high tensile strength/ high electrical resistivity/ resistant to corrosion.
Solder: Lead + Tin/ Pb + Sn.

Amalgam - an alloy in which mercury is one of the constituent/ Any metal + mercury.
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Question 45 Marks
Solution A turns universal indicator blue to purple whereas solution B turns universal indicator orange to red.
  1. What will be the action of solution A on litmus?
  2. What will be action of solution B on litmus?
  3. Name any two substances which can give solutions like A.
  4. Name any two substances which can give solutions like B.
  5. What sort of reaction takes place when solution A reacts with solution B?
Answer
  1. Solution A turns universal indicator blue to purple so it is basic in nature and will turn litmus blue.
  2. Solution B turns universal indicator orange to red so it is acidic in nature and will turn litmus red.
  3. Milk of magnesia and sodium hydroxide solution are bases like solution A.
  4. Lemon juice and hydrochloric acid are acids like solution B.
  5. Neutralisation reaction.
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Question 55 Marks
Write the chemical formula of ammonium chloride. Explain why an aqueous solution of ammonium chloride is acidic in nature? Illustrate your answer with the help of a chemical equation.
Answer
SOLUTION The chemical formula of ammonium chloride is $NH _4 Cl$. Since, ammonium chloride is the salt of a strong acid HCl and a weak base $NH _4 OH$, so an aqueous solution of ammonium chloride is acidic in nature. When dissolved in water, it gets hydrolysed to some extent to form HCl and $NH _4 OH . HCl$ being a strong acid is fully ionised and gives a large amount of hydrogen ions whereas $NH _4 OH$ is only slightly ionised. So, $NH _4 Cl$ contains more of hydrogen ions than hydroxide ions and is hence acidic in nature.
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Question 65 Marks
The pH values of five solutions A, B, C, D and E are given below:
  1. 1
  2. 5
  3. 7
  4. 11
  5. 13
Which solution is:
  1. Weakly alkaline.
  2. Neutral.
  3. Strongly acidic.
  4. Strongly alkaline, and.
  5. Weakly acidic?
Answer
  1. Solution D, with a pH value of 11, is weakly alkaline.
  2. Solution C, with a pH value of 7, is neutral.
  3. Solution A, with a pH value of 1, is strongly acidic.A.
  4. Solution E, with a pH value of 13, is strongly alkaline.
  5. Solution B, with a pH value of 5, is weakly acidic.
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Question 75 Marks
State two uses each of the following compounds:
  1. Sodium hydroxide.
  2. Chlorine.
  3. Hydrogen.
  4. Hydrochloric acid.
Answer
  1. Sodium hydroxide:
  1. It is used for making soaps and detergents.
  2. It is used in the manufacture of paper.
  1. Chlorine:
  1. It is used in the production of bleaching powder.
  2. It is used in the production of hydrochloric acid.
  1. Hydrogen:
  1. It is used in the production of hydrochloric acid.
  2. It is used in the hydrogenation of oils.
  1. Hydrochloric acid:
  1. It is used in medicines and cosmetics.
  2. It is used in textile/ dyeing and tanning industries.
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Question 85 Marks

In the following schematic diagram for the preparation of hydrogen gas as shown in Figure, what would happen if following changes are made?
  1. In place of zinc granules, same amount of zinc dust is taken in the test tube.
  2. Instead of dilute sulphuric acid, dilute hydrochloric acid is taken.
  3. In place of zinc, copper turnings are taken.
  4. Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.
Answer
  1. The reaction will become faster because zinc dust has more surface area.
  2. Nearly same amount of hydrogen gas will be evolved.
  3. No reaction will take place as copper is less reactive than hydrogen.
  4. The reaction will take place and hydrogen gas will be evolved.
$\text{Zn}\ \ +\ \ 2\text{NaOH}\ \ \xrightarrow{\text{heat}}\ \ \text{Na}_2\text{ZnO}_2\ \ +\ \ \text{H}_2\text{(g)}\\\text{Zinc}\ \ \ \ \text{Sodium}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{Sodium}\ \ \ \ \ \ \ \ \ \ \ \text{Hydrogen}\\ \ \ \ \ \ \ \ \ \ \ \ \text{hydroxide}\ \ \ \ \ \ \ \ \ \ \ \ \ \text{zincate}$
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Question 95 Marks
Write word equations and then balanced equations for the reaction taking place when–
  1. Dilute sulphuric acid reacts with zinc granules.
  2. Dilute hydrochloric acid reacts with magnesium ribbon.
  3. Dilute sulphuric acid reacts with aluminium powder.
  4. Dilute hydrochloric acid reacts with iron filings.
Answer
a. Zinc + Sulphuric acid Zinc sulphate + Hydrogen
$Zn+H_2 SO_4 \rightarrow ZnSO_4+H_2$
b. Magnesium + Hydrochloric acid magnesium chloride + Hydrogen gas
$Mg+2 HCl \rightarrow MgCl_2+H_2$
c. Aluminum + Sulphuric acid Aluminum sulphate + Hydrogen gas
$2 Al+3 H_2 SO_4 \rightarrow Al_2\left(SO_4\right)_3+3 H_2$
d. Iron + Hydrochloric acid Iron chloride + Hydrogen
$Fe+2 HCl \rightarrow FeCl_2+H_2$
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Question 105 Marks
With the help of labelled diagrams, describe an activity to show that acids produce ions only in aqueous solutions.
Answer
Activity: Take about 1g solid NaCl in a clean and dry test tube and add some concentrated sulphuric acid to it. Fit a rubber cork with a small delivery tube in the mouth of the test tube. Concentrated sulphuric acid reacts with sodium chloride to form hydrogen chloride gas. The hydrogen chloride gas starts coming out of the open end of the glass tube.

Now, hold a ‘dry’ blue litmus paper in HCl gas. There is no change in colour of the ‘dry’ blue litmus paper. This shows that HCl gas does not behave as an acid in the absence of water. However, when we hold a ‘moist’ blue litmus paper in HCl gas, we will see that the ‘moist’ blue litmus paper turns red. This indicates that HCl gas shows acidic behavior in the presence of water as hydrogen ions are formed. This proves that acids produce ions only in aqueous solutions or in presence of water.
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Question 115 Marks
Consider the following substances :$NaCl , Ca ( OH )_2, NaHCO _3, NH _3, Na _2 CO , H _2 O , Cl _2, CO _2, CaSO _4 \cdot 2 H _2 O , 2 CaSO _4 \cdot H _2 O , CaOCl _2$
  1. Which two substances combine to form bleaching powder?
  2. Which four substances are utilised in the production of washing soda?
  3. Which compound represents plaster of Paris?
  4. Which compound is a part of baking powder?
  5. Which compound is used as an antacid?
Answer
a. $Ca ( OH )_2$ and $Cl _2$
b. $NaCl , NH _3, H _2 O$ and $CO _2$
c. $2 CaSO _4 \cdot H _2 O$
d. $NaHCO _3$
e. $NaHCO _3$​​​​​​​
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Question 125 Marks
What does a soda-acid type fire extinguisher contain? How does it work?
Explain the working of a soda- acid fire extinguisher with the help of a labelled diagram.
Answer
Working: A soda-acid type fire extinguisher contains a solution of sodium hydrogencarbonate and sulphuric acid in separate containers in separate containers inside them. When the knob of the fire extinguisher is pressed, then sulphuric acid mixes with sodium hydrogencarbonate solution to produce carbon dioxide gas which forms a blanket around the burning substance and cuts off the supply of air to burning substance; this stops the process of burning and fire gets extinguished.
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Question 135 Marks
How would you distinguish between baking powder and washing soda by heating?
Answer
Baking soda is sodium hydrogen carbonate $\left( NaHCO _3\right)$ which forms sodium carbonate $\left( Na _2 CO _3\right)$, water and carbon dioxide gas while heating.
$2 NaHCO_3 \rightarrow Na_2 CO_3+H_2 O+CO_2 \uparrow$
Presence of $CO _2$ can be detected with the help of lime water which turns milky after reacting with carbon dioxide gas
Washing soda is sodium carbonate deca-hydrate $\left( Na _2 CO _3 \cdot 10 H _2 O \right)$ which means there are 10 water molecules present with crystal hence named as water of crystallization
On heating washing soda, it becomes anhydrous and presence of water of crystallization can be detected with the help of anhydrous $CuSO _4$ which shows colour change from white to blue with moisture.
$Na_2 CO_3 \cdot 10 H_2 O \rightarrow Na_2 CO_3+10 H_2 O$
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Question 145 Marks
A group of students measured the pH of some substances they found in their homes. Their results are given in the following table:
Sabstance pH Sabstance pH
Apples 3.0 Salt 7.0
Baking soda 8.5 Sugar 7.0
Black coffee 5.0 Toothpaste 9.0
Houshold ammonoa 12.0 Vinegar 3.0
Lemon juoce 2.5 Wasimg soda 11.5
Milk 6.0    
  1. What would the students have used to measure the pH?
  2. Which solution is the most acidic (c) Which solution is the most alkaline?
  3. Which solutions are neutral?
  4. Which solution can be used to treat wasp stings?
  5. Which solution can be used to treat bee stings?
Answer
  1. Universal indicator paper is used to measure the pH.
  2. Lemon juice with pH = 2.5 is the most acidic.
  3. Household ammonia with pH = 12 is the most alkaline.
  4. Salt solution and sugar solution with pH = 7 are neutral.
  5. Vinegar (acid) can be used to treat wasp stings since it injects an alkaline liquid into the skin.
  6. Baking soda can be used to treat bee stings since it injects methanoic acid into the skin.
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Question 155 Marks
Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Answer
Two nails are fitted on a cork and are kept it in a 100 mL beaker. The nails are then connected to the two terminals of a 6-volt battery through a bulb and a switch. Some dilute HCl is poured in the beaker and the current is switched on. The same experiment is then performed with glucose solution and alcohol solution.
Observations:
It will be observed that the bulb glows in the HCl solution and does not glow in the glucose solution.
Result:
HCl dissociates into $H^+$ and $Cl^-$ ions. These ions conduct electricity in the solution resulting in the glowing of the bulb. On the other hand, the glucose solution does not dissociate into ions. Therefore, it does not conduct electricity.
Conclusion:
From this activity, it can be concluded that all acids contain hydrogen but not all compounds containing hydrogen are acids.
That is why, though alcohols and glucose contain hydrogen, they are not categorised as acids.
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Question 165 Marks
Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formula of A, B and C.
Answer
Since in first reaction there is liberation of hydrogen gas on reaction with X. Metals liberate htdrogen gas on reaction with bases. Also in second reaction X react with acid to form water and B. Since acid react with base. So, X is a base. Most common base is Sodium hydroxide. The compound X is sodium hydroxide. Reaction: $\text{NaOH}+\text{Zn}\rightarrow\text{Na}_2\text{ZnO}_2+\text{H}_2$
Hence, compound A is sodium zincate $Na_2ZnO_2$ Reaction:$\text{NaOH}+\text{HCl}\rightarrow\text{NaCl}+\text{H}_2\text{O}$
Hence, compound B is sodium chloride NaCl Reaction:$\text{NaOH}+\text{CH}_3\text{COOH}\rightarrow\text{CH}_3\text{COONa}+\text{H}_2\text{O}$
Hence, compound C is sodium acetate. Thus, X is NaOH . A is sodium zincate $\left( Na _2 ZnO _2\right) B$ is common salt $( NaCl ) C$ is sodium acetate $\left( CH _3 COONa \right)$
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Question 175 Marks
A metal carbonate $X$ on reacting with an acid gives a gas which when passed through a solution $Y$ gives the carbonate back. On the other hand, a gas $G$ that is obtained at anode during electrolysis of brine is passed on dry $Y$, it gives a compound $Z$, used for disinfecting drinking water. Identity $X$, $Y$, $G$ and $Z$.
Answer
Here X is calcium carbonate which is a metal carbonate which reacts with dilute HCl to form calcium carbonate $\left( CaCO _3\right)$, water and carbon dioxide gas. $CaCO _3+$ dil. $2 HCl \rightarrow CaCl _2+ H _2 O + CO _2 \uparrow$
When carbon dioxide gas is passed through lime water or calcium hydroxide $\left( Ca ( OH )_2\right)$, it gives the calcium carbonate back. So Y is calcium hydroxide.
$Ca(OH)_2+CO_2 \rightarrow CaCO_3 \downarrow+H_2 O$
Brine is saturated solution of sodium chloride $( NaCl )$. Electrolysis of brine forms hydrogen gas at cathode and chlorine gas at anode.
$2 NaCl+2 H_2 O \xrightarrow{\text { Electrolysis }} 2 NaOH+Cl_2(g)+H_2(g)$
So G is chlorine gas which is passed through dry calcium hydroxide $\left( Ca ( OH )_2\right)$, produces bleaching powder, $CaOCl ( Z ) . Ca ( OH )_2+ Cl 2 \rightarrow CaOCl 2+ H _2 O Hence ^2, X =$ Calcium carbonate; $Y=$ Lime water; $G=$ Chlorine gas and $Z=$ Calcium oxychloride or bleaching powder
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Question 185 Marks
Compounds such as alcohol and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it.
Answer
Activity.
Take solutions of glucose, alcohol, hydrochloric acid and sulphuric acid. Fix two nails on a cork, and place the cork in a 100 ml beaker. Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch. Now pour some dilute HCl in the beaker and switch on the current. The bulb starts glowing. This shows that HCl solution taken in the beaker conducts electricity. If we replace hydrochloric acid with sulphuric acid and perform the experiment, the bulb would glow again. This shows that an aqueous solution of an acid conducts electricity due to the presence of charged particles called ions in it.

Now, if we take glucose solution in the beaker and switch on the current, the bulb would not glow. If we repeat the experiment by taking alcohol solution in the beaker, the bulb would not glow again. This shows that due to the absence of ions, glucose and alcohol solutions do not conduct electricity. From this activity, we conclude that the hydrogen containing compounds such as glucose and alcohol are not categorised as acids because they do not dissociate (or ionise) in water to produce hydrogen ions [H(aq) ions].
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Question 195 Marks
Describe how washing soda is produced starting from sodium chloride (common salt). Write equations of all the reactions involved.
Answer
  1. Production of washing soda: Washing soda is produced from sodium chloride (or common salt) in the following three steps:
  1. A cold and concentrated solution of sodium chloride (called brine) is reacted with ammonia and carbon dioxide to obtain sodium hydrogen carbonate:
$\ \ \ \ \ \ \text{N}\bar{\text{a}}\text{Cl}\ \ +\ \ \text{NH}_3\ \ +\ \ \text{H}_2\text{O}\ \ +\ \ \text{CO}_2\rightarrow\text{NaHCO}_3\ \ +\ \ \text{NH}_4\text{Cl}\\^{\text{Sodium chloride}}\ ^{\text{Ammonia}}\ \ \ \ \ \ ^{\text{Water}}\ \ \ \ \ \ \ \ ^\text{Carbon}\ \ \ ^{\text{Sodium hydrogen}}\ \ \ \ \ \ ^{\text{Ammonium}}\\\ ^{\text{(Common Salt)}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^{\text{dioxde}}\ \ \ \ \ \ ^{\text{Carbonate}}\ \ \ \ \ \ \ \ \ \ \ \ ^{\text{Chloride}}$

Sodium hydrogen carbonate formed is only slightly soluble in water, so it precipitates out as a solid.
  1. Sodium hydrogen carbonate is separated by filtration, dried and heated. On heating, sodium hydrogen carbonate decomposes to form sodium carbonate:
$\ \ 2\text{NaCHO}_3\ \ \xrightarrow{\text{Heat}}\ \ \text{Na}_2\text{CO}_3\ \ +\ \ \text{CO}_2\ \ +\ \ \text{H}_2\text{O}\\^{\text{Sodium hydrogen}}\ \ \ \ \ \ \ \ ^{\text{Sodium carbonate}}\ \ \ ^{\text{Carbonate}}\ \ \ \ \ \ ^{\text{Water}}\\\ \ \ \ \ ^\text{Carbonate}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^{\text{(Sodaash)}}\ \ \ \ \ \ \ \ \ \ ^{\text{dioxide}}$

The anhydrous sodium carbonate obtained here is called soda ash.
  1. Anhydrous sodium carbonate (soda ash) is dissolved in water and recrystallised to get washing soda crystals containing 10 molecules of water of crystallisation:
$\ \ \ \ \ \ \ \ \ \ \text{Na}_2\text{CO}_3\ \ \ \ \ \ \ \ \ +1\text{CH}_2\text{O}\rightarrow\ \ \ \text{Na}_2\text{CO}_3,1\text{CH}_2\text{O}\\^{\text{Anhydroussdiuumcarbonate}}\ \ \ \ \ \ ^{\text{Water}}\ \ \ \ \ \ \ \ ^{\text{Sodiumcarbonatedecahydrate}}\\\ \ \ \ \ \ \ \ \ \ \ \ \ ^{\text{(Sodaas)}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^{\text{(Washingsoda)}}$
  1. An aqueous solution of washing soda is alkaline because it turns red litmus to blue.
  2. Washing soda has detergent properties because it can remove dirt and grease from dirty clothes.
  1.  
  1. It is used as cleansing agent for domestic purposes.
  2. It is used for removing permanent hardness of water.
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