Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
(a) Hydrogen gas combines with nitrogen to form ammonia
H2 + N2 ---------→ NH3
Hydrogen gas nitrogen gas Ammonia
3H2 + N2 -----------→ 3NH3
Hydrogen gas NItrogen gas Ammonia
(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide
H2S(g) + O2(g) ----------------→ H2O(l) + SO2(g)
Hydrogen sulphide gas Oxygen (from air) water Sulpur dioxide
2H2S(g) + 3O2(g) --------------→ 2H2O(l) + 2SO2(g)
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate
BaCl2(aq) + Al2(SO4)3(aq) --------→ AlCl3(aq) + BaSO4(s)
Barium chloride Aluminium sulphate Aluminium chloride Barium sulphate
3BaCl2(aq) + Al2(SO4)3(aq) -------→ 2AlCl3(aq) + 3BaSO4(s)
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas
K(s) + H2O(l) -----→ KOH(aq) + H2(g)
Potassium Water potassium hydroxide hydrogen gas
2K(s) + 2H2O(l) ------- → 2KOH(q) + H2(g)
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.
Give an example of a double displacement reaction other than the one given in activity 1.10.
Why is respiration considered an exothermic reaction? Explain.
Identify the substances that are oxidised and the substance that are reduced in the following reactions.
(i) 4Na(s) + O2(g) → 2Na2O(s)
(ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction
Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g
What is a balanced chemical equation? Why should chemical equations be balanced?
A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.
What is a good source of energy?
Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
What changes can you make in your habits to become more environment-friendly?
What is the difference between a reflex action and walking?
What is the importance of DNA copying in reproduction?
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Define the principal focus of a concave mirror.
You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(c) The field consists of radial lines originating from the wire.
(d) The field consists of concentric circles centred on the wire.
Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
The phenomenon of electromagnetic induction is
(a) the process of charging a body.
(b) the process of generating magnetic field due to a current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.
People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?
Use the data in Table 12.2 to answer the following –
(a) Which among iron and mercury is a better conductor?
(b) Which material is the best conductor?
Calculate the number of electrons constituting one coulomb of charge.
The brain is responsible for
(a) thinking.
(b) regulating the heart beat.
(c) balancing the body.
(d) all of the above.
What is the role of the acid in our stomach?
Why should we conserve forests and wildlife?