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Question 1.
what is the difference between artery and veins?
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Question 2.
Where do plants get each of the raw material required for photosynthesis?
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Question 3.
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(l)
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Question 4.
Give an example of a double displacement reaction other than the one given in Activity 1.10.
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Question 5.
Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
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Question 6.
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:
Water contains two parts hydrogen and one part oxygen (two H and one O = H2O) Because of this, the amount of hydrogen and oxygen produced during electrolysis of water is in a 2:1 ratio.
In electrolysis process, hydrogen goes to one test tube and oxygen goes to another. Because Water contains 2 part hydrogen, the amount collected in one tube is double of amount collected in other one.
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Question 7.
1. 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) X = Calcium Oxide (CaO)
ii) CaO(s) + H2O(l) ---> Ca(OH)2(aq)
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Question 8.
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:
BaCl2(aq) + Na2SO4(aq) --- > BaSO4(s) + 2NaCl(aq)
NaOH(aq) + HCl(aq) ----> NaCl(aq) + H2O(l)
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Question 9.
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) ------> 2HCl(g)
ii) 3BaCl2(s) + Al2(SO4)3(s) --------> 3BaSO4(s) + 2AlCl3(s)3
iii) 2Na(s) + 2H2O(l) -----------> 2NaOH(aq) + H2(g)
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Question 10.
Why should a magnesium ribbon be cleaned before burning in air?
Answer: Magnesium is very reactive metal. When stored it reacts with oxygen to form a layer magnesium oxide on its surface. This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen. The magnesium ribbon is cleaned by sand paper to remove this layer so that the underlying metal can be exposed into air.
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