Question 1.
Fill in the blanks :
(a) In______________________change no new substance is formed.
(b) A foul smelling spoiled food is a_______________________change.
(c) Properties such as shape, size, colour and state of a substance are called____________ properties.
(d) Turning of lime water to milky is a standard test of_________________________gas.
(e) A chemical change is also called a_________________________
(f) Photosynthesis is an example of __________________________change.
(g) Burning of any substance is a____________________________change.
(h) Conditions for rusting of iron is ____________________and____________________
(i) The chemical name of vinegar is________________________________
Answer
(a) Physical
(b) Chemical
(c) Physical
(d) $CO_2$
(e) chemical reaction
(f) Chemical
(g) Chemical
(h) air and water
(i) Acetic Acid
Question 2.
Show with the help of chemical & word equation the chemical reaction between
(a) Vinegar and baking soda.
(b) Carbon dioxide and lime water.
(c) Burning of magnesium ribbon.
(d) Magnesium oxide and water.
(e) Rusting of iron & Copper sulfate and iron.
Answer
(a) baking soda (sodium bicarbonate) plus vinegar (acetic acid) yields carbon dioxide plus water plus sodium ion plus acetate ion
Vinegar (Acetic acid) + Baking soda (Sodium hydrogencarbonate) -> Carbon dioxide + other substances
$NaHCO_3 + CH_3C00H -> NaC_2H_3O_2 + H_2O + CO_2$
(b) They form water and Calcium Carbonate
$CO_2(g) + Ca(OH)_2(aq) -> CaCO_3(s) + H_2O(l)$
(c)Magnesium oxide is formed
$2Mg(s)+O_2 (g) -> 2MgO(s)+ energy$
(d)magnesium hydroxide
$MgO + H_2O -> Mg(OH)_2$.
(e) Fe(s) + Oxygen ($O_2$, from the air) + water ($H_2O$) -> rust (iron oxide $Fe_2O_3$)
Multiple Choice Questions
Question 3
Galvanisation is a process used to prevent the rusting of which of the following?
(a) Iron
(b) Zinc
(c) Aluminium
(d) Copper
Question 4
Which of the following statement is incorrect for a chemical reaction?
(a) Heat may be given out but never absorbed.
(b) Sound may be produced.
(c) A colour change may take place.
(d) A gas may be evolved
Question 5
Which of the following is a physical change?
(a) Rusting of iron
(b) Combustion of magnesium ribbon
(c) Burning of candle
(d) Melting of wax
Question 6
Which of the following is a chemical change?
(a) Twinkling of stars
(b) Cooking of vegetables
(c) Cutting of fruits
(d) Boiling of water
Answer
3. (a)
4. (a)
5. (d)
6. (b)
Short answer type
Question 7
Differentiate between physical and chemical change with 2 examples of each.
Question 8
Write down any 4 characteristics of chemical change.
Question 9
Why is it always advised not to play with fireworks?
Question 10
What is the role of the Ozone layer in our atmosphere?
