CHEMICAL REACTIONS AND EQUATIONS
Board Questions (2008-2014) and Answers
Q1(2008): What happens chemically when quick lime is added to water?
Answer:
Answer: The equation which is unbalanced because the mass is not the same on both sides of the equation, is a skeletal chemical equation for a reaction.
Q8: Identify the type of reaction in the following example:
Answer: Quick lime is CaO which reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.
CaO(s) + H2O(l) → Ca(OH)2(aq)
CaO(s) + H2O(l) → Ca(OH)2(aq)
Q2: A student burns magnesium ribbon in the lab and observes a white powder falling on the table. What type of reaction has taken place and name the white powder?
Answer: It is a chemical reaction. The white powder formed is magnesium oxide (MgO).
Q3: What are the essentials of a chemical reaction?
Answer:
- It should be balanced and confirm to the law of conservation of matter
- It should be molecular
- It must refer to an actual chemical equation
Q4: How will you test for the gas which is liberated when hydrochloric acid reacts with
an active metal?
Answer: When a burning match stick is brought near the mouth of the test tube in which reaction is taking place, it will burn with popping sound. It detects the presence of hydrogen (H2) gas.
Q5: What change in colour is observed when white silver chloride is left exposed to sunlight? What type of chemical reaction is this?
Answer: White silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine by light.It is a photo-chemical decomposition reaction.
2AgCl(s) —Sunlight—→ 2Ag(s) + Cl2(g)
Q6: Why is respiration considered as exothermic process?
Answer: In respiration heat is released so it is termed as an exothermic reaction.
C6H12O6 + 6O2 —→ 6CO2 + 6H2O + energy
Q7(2010):What is meant by skeletal equation?
Answer: The equation which is unbalanced because the mass is not the same on both sides of the equation, is a skeletal chemical equation for a reaction.
During exam, try to write chemical equations and chemical formulae in your answers wherever possible. It enhances visibility and gives you more scores.
Q8: Identify the type of reaction in the following example:
Na2SO4(aq) + BaCl2(aq) —→ BaSO4(s) + 2NaCl(aq)
Answer: A double displacement reaction.
Q9: Why are bags of chips flushed with nitrogen gas?
Answer: Chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised.
Q10 : What is precipitation reaction?