10th Class Physics 1st Lesson Chemical Reactions and Equations Questions and Answers (In Textbook)
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Question 1.Why should a magnesium ribbon be cleaned before burning in air ?
Answer: Magnesium ribbon should be cleaned with sand paper before burning in air order to remove white layer of magnesium oxide (MgO) from its surface which hinders the burning of magnesium.
Question 2.Write the balanced equation for the following chemical reactions.
i) Hydrogen + Chlorine → Hydrogen chloride
ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
iii) Sodium + Water → Sodium hydroxide + Hydrogen
Answer:
i) H2(g) + Cl2(g) → 2HCl2(g)
ii) 3BaCl2(aq) + Al2(SO4)3(aq) → 3BaSO4(s) + 2AlCl3(aq)
iii) 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
Question 3.Write a balanced chemical equation with state symbols for the following reactions.
i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Answer:
i) BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)
ii) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O (l)
Question 4.A solution of a substance ‘X’ is used for white washing.
i) Name the substance ‘X’ and write its formula.
ii) Write the reaction of the substance ‘X’ named in (i) above with water.
Answer:
i) For white washing a solution quick lime is used. The substance ‘X’ is quick lime and its formula is CaO (Calcium oxide)
ii) When quick-lime reacts with water, the following reactions takes place.
Question 5. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other ? Name this gas.
Answer:
During electrolysis, water decomposes to form hydrogen and oxygen gases.
In the above reaction, the balanced chemical equation shows that an electrolysis, the water decomposes to form hydrogen and oxygen in the ratio of 2 : 1 by volume.
Question 6.Why does the colour of copper sulphate solution change when an iron nail is dipped in it ?
Answer:
Iron is more reactive element than copper. When an iron nail is dipped in copper sulphate solution which is blue in colour, iron being more reactive than copper displaces copper from copper sulphate and forms, iron (II) sulphate which is green in colour.
Question 7.Give an example of a double displacement reaction other than the one given in Activity 1.10.
Answer:
AgNO3 (aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
Question 8.Identify the substances that are oxidised and the substances that are reduced in the following reactions.
i) 4Na(s) + O2(g) → 2Na2O(s)
ii) CuO(s) + H2(g) → Cu(s) + H2O(I)
Answer:
i) Na has gained oxygen and forms Na20. So, Na is oxidised and O2 is reduced.
ii) CuO has lost oxygen and forms Cu. So, CuO is reduced and H2 which has gained oxygen is oxidised.
Group Activity (Page No : 34)
Take four beakers and label them as A, B, C and D.
Put 25 ml of water in A B and C beakers and copper sulphate solution in beaker D.
Measure and record the temperature of each liquid contained in the beakers above.
Add two spatulas of potassium sulphate, ammonium nitrate, anhydrous copper sulphate and fine iron fillings to beakers A, B, C and D respectively and stir.
Finally measure and record the temperature of each of the mixture above.
Find out which reactions are exothermic and which ones are endothermic in nature.
Answer:
Take four beakers and label them as A, B, C and D.
Put 25 ml of water in A, B and C beakers and copper sulphate solution in beaker D.
Measure and record the temperature of each liquid contained in the beakers above.
Add two spatulas of potassium sulphate, ammonium nitrate, anhydrous copper sulphate and fine iron fillings to beakers A, B, C and D respectively and stir.
Finally measure and record the temperature of each of the mixture above.
In A, C and D beakers heat is evolved during a reaction the reaction can be exothermic reaction.
In B beaker heat is absorbed during a reaction the reaction can be endothermic reaction
AP 10th Class Physical Science Chapter 1 Questions and Answers (Lab Activities)
Activity – 1.1 (Page No. 4)
Question 1.
Write the procedure and observations in the reaction of magnesium and oxygen.Answer:Aim : To show that burning of magnesium ribbon in air is a combination reaction.
Materials required : Magnesium wire, Tong, Burner.
Procedure:
1) Take a strip of magnesium ribbon and hold it with the help of tong.
2) Introduce it into the flame of the burner.Observation Magnesium ribbon burns with a dazzling white flame and changes into a white powder.
Chemical Reaction :
Conclusion :
Burning of magnesium in presence of oxygen to form magnesium oxide is a combination reaction and an exothermic process because heat and light are produced.
Activity – 1.2 (Page, No. 6)
Question 2.
Take lead nitrate solution in a test tube.Add potassium iodide solution to this. What do you observe? How do you classify the reaction ?Answer:
When you add potassium iodide (KI) solution to lead nitrate (Pb(NO3))2 solution in a test tube, you will observe the formation of a yellow precipitate.
This reaction is a classic example of a double displacement reaction, also known as a precipitation reaction.
The balanced chemical equation for this reaction is as follows :
Pb(NO3))2(aq) + 2KI(aq) → Pbl2(s) + 2KNO3(aq)
Activity – 1.3 (Page, No. 6)
Question 3.
Write an activity to show the change in temperature in a chemical reaction.
(Or)
Take a few zinc granules in a conical flask or a test tube. Add dilute hydrochloric acid or sulphuric acid to this (Figure).
Do you observe anything happening around the zinc granules ?
Touch the conical flask or test tube. Is there any change in its temperature ?
Answer:
Aim : To formation of hydrogen gas by the action of dilute sulphuric acid on Zinc.
Materials required Conical flask, Zinc granules, Dilute sulphuric acid, Glass tube, Cork.
Procedure :
Take a few zinc granules in a conical flask.
Add dilute sulphuric acid to this.
Observe happening around the zinc granules.
Touch the conical flask and observe any change in its temperature.
Observation :
Formation of hydrogen gas the action of dilute sulphuric acid on zinc. It is an exothermic process because heat is evolved.
Chemical Reaction :
Zn + H2SO4 → ZnSO4 + H2
Conclusion : This is exothermic process because heat is evolved.
Activity – 1.4 (Page, No. 14)
Question 4.
Write an activity to show a chemical combination reaction.
Answer:
Aim :
To show that combination reaction between calcium oxide and water is an exothermic process.
Materials required :
Quick lime (Calcium oxide), Water, Beaker
Procedure :
1) Take a small amount of calcium oxide or quick lime in a beaker.
2) Slowly add water to this.
3) Touch the beaker.
4) Note down the observations.
Observations :
Calcium oxide reacts with water vigorously to form calcium hydroxide with the evolution of heat.
Chemical Reaction :
Conclusion :
The reaction between CaO (calcium oxide) and H2O is a combination reaction. It is an exothermic process because heat is evolved.
Activity – 1.5 (Page. No. 18)
Question 5.
Write an activity to show a decomposition reaction.
Answer:
Aim :
To show thermal decomposition reaction of ferrous sulphate.Materials required : Ferrous sulphate crystals, dry test tube, burner.
Procedure :
Take 2g of ferrous sulphate crystals in a dry test tube.
Note the colour of the ferrous sulphate crystals.
Heat the boiling tube over the flame of a burner for some time.
Observe the colour of the crystals after heating.
Observation :
The pale green colour of ferrous sulphate crystals changes to reddish brown ferric oxide and smell of burning sulphur is observed.
Chemical Reaction :
Ferrous sulphate ----->Ferric oxide
Conclusion :
Heating of ferrous sulphate is a thermal decomposition because ferrous sulphate braks into simpler compounds Fe2O3, SO2 and SO3.
Activity – 1.6 (Page. No. 18)
Question 6.
a) Design an activity to demonstrate the decomposition reaction of lead nitrate.
b) Draw labelled diagram of the exp : ntal setup. List two main observations.
c) Write balanced chemical equation for the reaction stating the physical state of the reactant and products.
Answer:
a) Activity :
Take a boiling tube and put about 3g lead nitrate powder in it.
Hold the boiling tube carefully with a pair of tongs.
Now, heat the tube over a flame.
b) Observations :
Brown fumes of nitrogen dioxide gas is observed.
Lead oxide, a yellow compound is formed.
Activity – 1.7 (Page. No. 20)
Question 7.
plain electrolysis of water with an activity (or) With the help of an activity explain that H2 and O2 are released when an electric current is passed through vater.
Answer:
Aim :
To demonstrate electrolysis of water.
Materials required :
Plastic mug, drilling machine, two graduated measuring cylinder, carbon electrodes, 6 volt battery, dil H2SO4, Water.
Procedure :
Take a plastic mug. Drill two holes at its base and fit rubber stoppers in these holes. Insert carbon electrodes in these rubber stoppers as shown in figure.
Connect these electrodes to a 6-volt battery.
Fill the mug with water such that the electrodes are immersed. Add a few drops of dilute sulphuric acid to the water.
Take two test tubes filled with water and invert them over the two carbon electrodes.
Switch on the current and leave the apparatus undisturbed for some time.
You will observe the formation of bubbles at both the electrodes. These bubbles displace water in the test tubes.
Observe the volume of gases collected in respective test tubes.
Once the test tubes are filled with the respective gases, remove them carefully.
Test these gases one by one by bringing a burning candle close to the mouth of the test tubes.
Observation :
The volume of one gases, i.e., hydrogen is twice the volume of other gas. One of the gases catches fire and burns with ‘pop’ sound where as in other gas, e.g. oxygen, match-stick burns brightly.
Conclusion :
Water on electrolysis decomposes to hydrogen and oxygen gas.
Activity – 1.8 (Page. No. 20)
Question 8.
Write an activity to show the decomposition reaction by using light.Answer:
Aim :
To show photochemical decomposition of silver chloride.
Materials required :
AgNO3(aq), NaCl(aq), test tubes.
Procedure :
Take about 2g silver chloride in a china dish.
Observe the colour of silver chloride.
Place this china dish in sunlight for some time.
Observe the colour of the silver chloride after some time.
Observation :
White silver chloride turns grey in sunlight because silver metal is formed.
Chemical Reaction :
Conclusion:
Decomposition of silver chloride in presence of sunlight is photochemical decomposition reaction.
Activity – 1.9 (Page. No. 22)
Question 9.
Write an activity to show the chemical displacement reaction.
Answer:
Aim :
To show reaction between Iron nails and copper sulphate solution.
Materials required :
Copper sulphate solution, Iron nail, Test tube, Thread, Stand.
Procedure :
Take three iron nails and clean them by rubbing with sand paper.
Take two test tubes marked as (a) and (b). In each test tube, take about 10 ml copper sulphate solution.
Tie two iron nails with a thread and immerse them carefully in the copper sulphate solution in test tube (b) for about 20 minutes. Keep one iron nail a side for comparison.
After 20 minutes, take out the iron nails from the copper sulphate solution.
Compare the intensity of the blue colour of copper sulphate solution in test tubes (a) and (b).
Also, compare the colour of the iron nails dipped in the copper sulphate solution with the one kept aside.
Observation :
The iron nail become brownish in colour and the blue colour of copper sulphate solution fades.
Chemical Equation :
Conclusion :
In this reaction, iron has displaced or removed another element, copper, from copper sulphate solution.
Activity – 1.10 (Page. No. 24)
Question 10.
Explain double displacement reaction with an activity.
Answer:
Aim :
To show reaction between sodium sulphate solution and barium chloride solution is double displacement reaction (precipitation reaction)
Materials required :
Barium chloride solution, sodium sulphate solution, two test tubes.
Procedure:
Take about 3 ml of sodium sulphate solution in a test tube.
In another test tube, take about 3 ml of barium chloride solution.
Mix the two solutions.
Observation :
White precipitate is formed.
Chemical Reaction :
Conclusion :
Reaction between sodium sulphate solution and barium chloride solution is double displacement reaction. It is also called precipitation reaction.
Activity – 1.11 (Page. No. 26)
Question 11.
Write an activity to understand the Oxidation and Reduction reaction.
Answer:
Aim :
To prepare copper oxide and to show the redox reaction of copper oxide with hydrogen gas.
Materials required :
Copper powder, China dish, Wire guaze, Tripod stand, Burner.
Procedure:
Heat a china dish containing about 1 g copper powder.
Pass the air over heated copper powder. Note down the observations.
Now pass the hydrogen gas over the heated copper oxide. Record the observations after sometime.
Observation :
Copper reacts with Air (oxygen) on heating to form copper oxide which is black. Now pass the hydrogen gas over the heated copper oxide, the black coating on the surface turns pink (reddish brown).
Chemical Reaction :
Conclusion :
The reaction between copper oxide and hydrogen is redox reaction. Copper oxide is oxidising agent whereas hydrogen is reducing agent.
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