Extra questions on chemical reactions and equations
Answers
Answer:
Explanation:
Question 1.
How does the food become rancid?
Answer:
Food becomes rancid when fat and oils present in the food are oxidised.
Question 2.
A student burnt a metal A found in the form of ribbon. The ribbon burnt with a dazzling flame and a white powder B was formed which was basic in nature. Identify A and B. Write the balanced chemical equation.
Answer:
X = Mg, Y = MgO, Mg + O2 → 2MgO
Question 3.
What is a balanced chemical equation?
Answer:
An equation that has equal number of atoms of each element on both the sides of the equation is called a balanced chemical equation, i.e., mass of the reactants is equal to mass of the products.
For example, 2Mg+O2⟶Δ2MgO
Question 4.
Write a balanced equation for a chemical reaction that can be characterised as precipitation.
Answer:
BaCl2(aq) + Na2SO4 (aq) → BaSO4(s) + 2NaCl(aq)
Question 5.
What is rust?
Answer:
It is a brown mass known as hydrated ferric oxide. Its formula is Fe2O3. xH2O.
Question 6.
A zinc rod is left for nearly 20 minutes in a copper sulphate solution. What change would you observe in the zinc rod?
Answer:
The zinc rod will change into zinc sulphate.
Question 7.
Name two salts that are used in black and white photography.
Answer:
Both silver chloride and silver bromide are used in black and white photography.
Question 8.
Which chemical process is used for obtaining a metal from its oxide?
Answer:
The process is known as the reduction of metal oxide.
Question 9.
If you collect silver coins and copper coins you may have seen that after some days a black coating forms on silver coins and a green coating on copper coins. Which chemical phenomenon is responsible for these coatings? Write the chemical name of the black and green coatings.
Answer:
Corrosion is responsible for the formation of this coating. Black coating is due to formation of Ag2S and green coating is due to formation of CuCO3.Cu(OH)2.
Question 10.
When carbon dioxide is passed through lime water, it turns milky, why?
Answer:
Lime water (calcium hydroxide) combines with carbon dioxide to form a suspension of calcium carbonate which makes lime water milky.
Ca(OH)2 + CO2 → CaCO3 + H2O
Question 11.
Identify the most reactive and least reactive metal: Al, K, Ca, Au.
Answer:
Most reactive metal: K(Potassium); least reactive metal: Au(gold).
Question 12.
X + Y SO4 → X SO4 + Y
Y + X SO4 → No reaction
Of the two elements T and Y which is more reactive and why?
Answer:
‘X’ is more reactive than ‘Y since it has displaced ‘Y’ in the displacement reaction.
Question 13.
Why is it necessary to balance a chemical equation?
Answer:
An equation is balanced in order to satisfy the law of conservation of mass according to which total mass of the reactants is equal to the total mass of the products, i.e., mass can neither be created nor be destroyed during any chemical change.
Question 14.
During electrolysis of water, the gas collected in one test tube is double than the other, why?
Answer:
On electrolysis, water decomposes into hydrogen and oxygen in the ratio 2 : 1 by volume so, H2 gas collected in one test tube is double than O2.
Question 15.
Represent decomposition of ferrous sulphate with the help of balanced chemical equation.
Answer:
2FeSO4 (s) → Fe2O3 (s) + SO2 (g) + SO3 (g)
Question 16.
What is a chemical equation?
Answer:
A chemical equation is a symbolic notation that uses formulae instead of words to represent a chemical equation.
Question 17.
A teacher took a few crystals of sugar in a dry test tube and heated the test tube over a flame. The colour of sugar turned black. Explain why?
Answer:
Sugar is a complex compound which on heating undergoes decomposition. Water gets evaporated thereby leaving behind black carbon in the test tube.
Question 18.
Name two metals which do not get corroded.
Answer:
Gold (Au) and platinum (Pt) do not get corroded.
Question 19.
Identify the compound oxidised in the following reaction:
H2S (g) + Cl2 → S(s) + 2HCl (g)
Answer:
H2S is oxidised.
Question 20.
Why is a magnesium ribbon cleaned before burning?
Answer:
Magnesium reacts with moist air and forms a layer of oxide, MgO (white), on its surface. So, a magnesium ribbon is cleaned to remove the oxide layer before burning.
Question 21.
State the chemical change that takes place when limestone is heated.
Answer:
Calcium carbonate decomposes on heating to give calcium oxide and carbon dioxide.
ALL THE BEST!!!!