This post explains the answers of questions of worksheet 4 taken from science and technology class 10 Chapter 4 Science.
Chemical reactions and Equations Worksheet 4 Answers
Q1. How do chemical reactions impact our life? Give reasons in support of your answer.
Answer
Chemical reactions play important role in our life. These reactions involve in our body, kitchen, surroundings.
1.Digestion and respiration in our body are chemical reactions, through them energy is produced.
2.When we cook food, chemical reactions change taste and smell of food.
3.Fule like petrol and diesel combust through chemical reaction to run a vehicle.
4.Soap and detergents remove dirt through chemical reaction and disinfectants kill germs by reaction.
5.Plants prepare food through photosynthesis process which a chemical reaction.
So, these are some examples of chemical reactions that impact our life and without them our life is not possible.
Q2. If a piece of a copper wire is dipped in silver nitrate solution. It becomes silver and colour of solution changes to blue. Name the type of equation(reaction) and write the balanced equation.
Answer
When a piece of copper wire is dipped into silver nitrate solution, copper displaces silver from silver nitrate and forms copper nitrate solution and silver metal gets deposited on copper wire so it becomes silver.
Displacement reactions take place.
Cu + AgNO3(aq) → Cu(NO3)2(aq) + Ag
Copper is more reactive than silver so it displaces from its compound. The colour of copper nitrate solution is blue.
Q3. ‘Gain of electron is reduction and loss of electron is oxidation’. Justify the statement.
Oxidation
When an atom or ion loses one or more electrons and become positively charged particle, this is oxidation reaction.
Na →Na+ + e–
Sodium loses one electron to form sodium cation. This is oxidation.
If a substance loses electrons and decreases negative charge, its oxidation number increases so it is oxidation.
Reduction
When an atom or ion gains one or more electrons and become negatively charged particle, this is reduction reaction.
Cl2 + e– → 2Cl–
Chlorine molecule gain electron to form chloride ions. This is reduction.
If a substance gains electrons and increase negative charge, its oxidation number decreases so it is reduction.
Q4. There is a reaction given below:
H2SO4(aq) + NaOH→ Na2SO4(aq) + H2O
Balance this equation and mention the steps for balancing this equation.
Answer
Steps for balancing equation
Step 1: Write unbalanced equation
H2SO4(aq) + NaOH→ Na2SO4(aq) + H2O
Step 2: Count the number of atoms of each elements on both sides
|
Elements |
Left |
Right |
|
H |
2+ 1=3 |
2 |
|
S |
1 |
1 |
|
O |
4+1 =5 |
4+ 1 =5 |
|
Na |
1 |
2 |
Step 3: Balance Na atoms
We can see numbers of atoms of sodium is different at both sides, so we balance Na atoms.
Write 2 before NaOH at left side
H2SO4(aq) + 2NaOH→ Na2SO4(aq) + H2O
Now we will re calculate numbers of atoms at both sides
|
Elements |
Left |
Right |
|
H |
2 + 2=4 |
2 |
|
S |
1 |
1 |
|
O |
4 +2 =6 |
4 + 1 =5 |
|
Na |
2 |
2 |
Step 4: Balance hydrogen and oxygen
Write 2 before H2O at right side then calculate
H2SO4(aq) + 2NaOH→ Na2SO4(aq) + 2H2O
|
Elements |
Left |
Right |
|
H |
2 + 2=4 |
2 +2=4 |
|
S |
1 |
1 |
|
O |
4 +2 =6 |
4 + 2 =6 |
|
Na |
2 |
2 |
We can see all atoms at both sides are equal so the reaction is now balanced.
H2SO4(aq) + 2NaOH→ Na2SO4(aq) + 2H2O
Q5. The smell or taste of the fat/oil containing food material change if left for a long time. Using your knowledge about chemistry, write the ways to prevent it.
Answer
When fat or oil containing food items are kept for a long time, they react slowly with oxygen in the air and get oxidised. This reaction of oxidation is called rancidity.
Due to rancidity, smell and taste of food items change.
Ways to prevent rancidity
1.Food items must be stored in air tight containers.
2.We should keep food items in cool places or refrigerator.
3.Add natural antioxidants
4.Remove air form packets and add nitrogen gas to avoid oxidation.
Q6. Do you think a combination reaction is opposite of decomposition reaction. Justify this with examples.
Answer
|
Combination |
Decomposition |
|
When two or more substances combine to form a single product, the reaction is called combination reaction. |
The reaction in which a single complex substance breaks down into two or more simpler substances, is called decomposition reaction. |
|
2H2 + O2 →2H2O |
2H2O → 2H2 + O2 |
In combination reaction, hydrogen and oxygen combine to form water.
In decomposition reaction, water molecule breaks down into hydrogen and oxygen.
Q7. Compare the packing and expiry date of namkeen packet and ordinary plastic packed namkeen. Which will last longer and why?
Answer
Branded namkeen packets are filled with nitrogen gas which does not react with fats or oil in namkeen, so food items do not get rancid(oxidised) and remain fresh for long time.
But on the other hand, ordinary plastic packets contain oxygen which reacts slowly with fats or oil and make namkeen rancid.
So, Nitrogen packed namkeen will last longer than ordinary packed namkeen
Q8. The marble stones often slowly get corroded when kept in open for a long time. Give reason in support of your answer.
Answer
Marble stones are made of calcium carbonate (CaCO3). When they are kept
open for a long time, they get corroded because of following reasons-
1.They react with pollutants like CO2 , SO2 and oxides of nitrogen. They get corroded.
2.Acid rain dissolve calcium carbonate and corrode marble stones.
CaCO3 + H2SO4 → CaSO4 +H2O + CO2
Q9. Do you think respiration and digestion of living being can be categorize as exothermic reaction? If yes, give reasons on support of your answer.
Answer
Yes, respiration and digestion in living beings are exothermic reactions.
Reasons
1.Respiration: Food(glucose) in our body reacts with oxygen and release energy in the form of ATP , CO2 and water
C6H12O6 + O2 →6CO2 + 6H2O + energy
Since energy is released in the respiration so it is exothermic reaction.
2.Digestion: Complex food like carbohydrate, fat and proteins are broken down into simpler substances. Glucose undergoes cellular respiration to release energy.
So, digestion is also an exothermic reaction.
Q10.We used choona pathar(quick lime) solution for whitewashing of our home. How this quick lime is obtained? When we mix it with water, after some time, it starts boiling. How does it happen? Explain with reasons.
Answer
How quick lime is obtained
When limestone (calcium carbonate) is heated at high temperature (900ºC), it
decomposes into quick lime (calcium oxide) and carbon dioxide.
CaCO3 →CaO +CO2
When quick lime is added into water, it forms slaked lime () and a large amount of heat is produced. Due to this heat, the solution starts boiling.
CaO + H2O→ Ca (OH)2 + heat
This reaction is exothermic reaction.
NIOS Class 10 Science Worksheet Solutions
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