Annual Examination – Set 2 വാർഷിക പരീക്ഷ

The scientist who proposed that electrons revolve round the nucleus only in certain definite orbits, each with a definite energy, is

An atom has the electron configuration 2, 5 and 7 neutrons in its nucleus. Its atomic number is and its mass number is .

Helium, neon and argon normally do not take part in chemical reactions because

Pick the odd one out and give the reason:   scandium (2, 8, 9, 2),  titanium (2, 8, 10, 2),  calcium (2, 8, 8, 2),  vanadium (2, 8, 11, 2).

Aluminium burns in oxygen:   4Al + 3O₂ → 2Al₂O₃. Which statement is correct?

When reactants are heated, the reaction usually becomes faster. The main reason is that

Find the relation and fill in:   Haber process : iron  ::  contact process :

Hollow, cage-like spheres made of carbon atoms arranged in pentagons and hexagons are called

Which of these is a use of carbon monoxide, not of carbon dioxide?

The IUPAC name of CH≡C–CH₂–CH₂–CH₂–CH₃ is

An atom of potassium is written as 3919K. (a) Find the number of protons, electrons and neutrons in it. (b) Write its electron configuration. How many electrons are there in its outermost shell, and which shell (K, L, M or N) is it?

The electron configurations of four elements are given (the letters are not their real symbols):   P 2, 8, 8  ·  Q 2, 8, 8, 2  ·  R 2, 7  ·  S 2, 8, 1. Find the group number of each and name the family to which it belongs.

Use the electronegativity values of Fig 3.12 (Si 1.90, Cl 3.16, K 0.82, Br 2.96). Find the electronegativity difference in (a) silicon tetrachloride, SiCl₄   (b) potassium bromide, KBr. Say whether each compound is ionic or covalent.

Say whether each change is oxidation or reduction. Give the reason.
(a) Mg → Mg²⁺ + 2e⁻   (b) Br + e⁻ → Br⁻   (c) Cu²⁺ + 2e⁻ → Cu   (d) S²⁻ → S + 2e⁻

(a) Sort these into fast and slow reactions:   inflating of a car air bag; rusting of an iron gate in the monsoon; white precipitate forming when silver nitrate solution is added to salt solution; weathering of rocks. (b) Give one reason why it is good for us that rusting of iron is a slow reaction.

Ammu adds sugar to a glass of lime juice and stirs. After a while, however much she stirs, some sugar stays at the bottom; the temperature does not change. (a) What kind of solution is the lime juice now? Why? (b) How can she make the remaining sugar dissolve without adding any more water or juice? (c) She does this, and then lets the glass cool slowly without disturbing it. No sugar separates. What kind of solution is it now?

Ravi has a white powder and wants to know whether it is a carbonate. He dissolves it in water and adds barium chloride solution: a white precipitate forms. (a) What does this show? (b) What must he do next to confirm that the salt is a carbonate, and what will he see?

(a) An alkene has 9 carbon atoms. How many hydrogen atoms does it have? Write its molecular formula and IUPAC name. (b) Do the same for an alkyne with 8 carbon atoms.

The figure shows an incomplete orbit diagram of a silicon atom; only the electrons of the K shell are drawn. (a) Write the atomic number and mass number of silicon. (b) Copy the diagram and complete it by drawing the electrons in the L and M shells. Write the electron configuration. (c) According to Bohr, which of the shells K, L and M has the highest energy? If an electron moves from the L shell to the M shell, is energy absorbed or given out?

Meera’s teacher shows four compounds: nickel sulphate (green), potassium dichromate (orange), cobalt nitrate (pink-red) and common salt, sodium chloride (white). (a) Name the element in each coloured compound that belongs to the transition elements. (b) Why is sodium chloride not coloured? (c) The elements of groups 3 to 12 are called transition elements. Why?

Ammonia (NH₃) is a covalent compound (N: Z = 7; H: Z = 1). (a) Write the electron configuration of nitrogen. How many more electrons does it need to complete its octet? (b) Draw the electron dot diagram of an NH₃ molecule (use dots for the electrons of nitrogen and crosses for those of hydrogen). (c) How many single bonds are there in NH₃? How many electrons are there around the nitrogen atom after bonding?

Boxes P and Q have the same volume and are at the same temperature. They contain the particles of two gases that react with each other. (a) Which box has the higher concentration of reactants? What is meant by concentration here? (b) In which box will the reaction be faster? Explain using collision theory. (c) Not every collision between the particles gives the products. Which collisions do? What is threshold energy?

In an experiment at 20 °C, 9 g of common salt was just enough to saturate 25 g of water; no more would dissolve. (a) Find the solubility of common salt at 20 °C. (b) Find the mass percentage of salt in this saturated solution. (c) What is the least mass of water at 20 °C needed to dissolve 18 g of common salt completely?

The figure shows the laboratory preparation of carbon dioxide. Dilute hydrochloric acid is poured through A on to the solid B. (a) Name the apparatus A and the substance B. (b) Write the balanced equation for the reaction in the flask. (c) Why is the gas collected in an upright jar C? What will you see when the gas is passed into clear lime water?

In the science club, Anu compares water (H₂O) and carbon dioxide (CO₂). Electronegativity values (Fig 3.12): H 2.20, C 2.55, O 3.44. (a) Find the electronegativity difference of the O–H bond and of the C=O bond. Are these bonds ionic or covalent? (b) In the O–H bond, which atom gets the partial negative charge (δ−)? Draw a water molecule and mark δ+ and δ−. (c) Both molecules have polar bonds, yet water is a polar molecule and carbon dioxide is non-polar. Why? (d) Water has a low molecular mass, but it is a liquid at room temperature. Which attraction between water molecules is responsible?

Bordeaux mixture is sprayed on coconut palms and arecanut trees. Rajan dissolved copper sulphate in water in an old iron bucket and left it overnight. Next morning the blue colour had become paler and a reddish-brown coating of copper had formed on the inside of the bucket:   Fe + CuSO₄ → FeSO₄ + Cu. (a) Write the equations showing the change in an iron atom and in a copper ion (Cu²⁺). (b) Which is oxidised and which is reduced? Give the reason. (c) Name the oxidising agent and the reducing agent. (d) Why did the blue colour become paler? Why do farmers prepare copper sulphate solution in plastic vessels, not in iron ones?

For the school science fair, Nithya studies the solubility of three salts in water. The table and the graph give the solubility in grams per 100 g of water.

Temperature (°C)	10	20	40	60	80
KNO₃	21	32	62	106	167
NH₄Cl	24	37	41	55	66
NaCl	36	36	36	37	37

(a) Which salt is more soluble at 20 °C: potassium nitrate or ammonium chloride? Which is more soluble at 60 °C? (b) What is the lowest temperature at which 62 g of potassium nitrate can dissolve completely in 100 g of water? (c) 55 g of ammonium chloride is dissolved in 100 g of water at 60 °C. Is the solution saturated or unsaturated? If it is heated to 80 °C, how much more ammonium chloride can it dissolve? (d) Which salt’s solubility changes the least with temperature? If a saturated solution of it in 100 g of water is cooled from 80 °C to 20 °C, about how much salt separates?

In a chemistry class in Kochi, the teacher draws two hydrocarbons, P and Q. (a) Write the molecular formula of P and of Q. What do you notice? (b) Write the IUPAC names of P and Q. (c) Q belongs to a homologous series. Name the series and write its general formula. Draw the structural formula of the member that comes just before Q. (d) Is P an alicyclic or an aromatic compound? Give the reason.