Model Test Paper മാതൃകാ ചോദ്യപേപ്പർ
A full paper in the Kerala Class 9 Chemistry pattern, covering the whole of “Chemical Bonding” – the octet, ionic bonds and ion formation, electron dot diagrams, covalent single, double and triple bonds, properties of ionic and covalent compounds, electronegativity and polarity, hydrogen bonding, valency and writing formulae of compounds, acids, bases and salts. Work on paper with a timer before you look at the solutions.
Standard IX · Chemistry
Chapter 3 · രാസബന്ധനം · Chemical Bonding
- The first 15 minutes are cool-off time: read every question and plan your answers; do not write.
- Answer all questions. Marks for each question are shown on the right.
- Write electron configurations like 2, 8, 1. In dot diagrams show only the outermost electrons; use dots for one atom and crosses for the other.
- When you decide the type of a bond, show the electronegativity difference. Electronegativity values (Fig 3.12) you may need:
Element H Li C N O F Al P S Cl K Ca Electronegativity 2.20 0.98 2.55 3.04 3.44 3.98 1.61 2.19 2.58 3.16 0.82 1.00
SECTION AAnswer all · 8 × 1 = 8 marks
1.
Which pair of elements is most likely to form an ionic compound? (Use the electronegativity values given.)
(1)(a) carbon and sulphur(b) nitrogen and hydrogen(c) lithium and chlorine(d) phosphorus and chlorine
2.
An atom that gains electrons becomes a negatively charged ion called .
(1)3.
Which of these ions does not have the same electron configuration as neon (2, 8)?
(1)(a) Na+(b) Mg2+(c) F−(d) K+
4.
Find the relation and fill in: MgO : ionic bond :: H2S :
(1)5.
The valency of sulphur (Z = 16) is .
(1)6.
Pick the odd one out and give the reason: KCl, CaO, PCl3, LiF
(1)7.
The correct formula of calcium nitrate is
(1)(a) CaNO3(b) Ca2NO3(c) Ca(NO3)2(d) Ca2(NO3)3
8.
Which of the following is a property of covalent compounds?
(1)(a) very high melting points(b) conduct electricity when molten(c) dissolve in organic solvents such as kerosene(d) hard crystalline solids
SECTION BAnswer all · 5 × 2 = 10 marks
9.
Potassium (Z = 19) and sulphur (Z = 16) take part in ionic bonding. (a) Write the equations for the formation of the potassium ion and the sulphide ion from the atoms. (b) Write the electron configurations of the two ions. Which noble gas do both resemble?
(2)10.
Hydrogen sulphide (H2S) is the gas that smells of rotten eggs. Draw the electron dot diagram of an H2S molecule (H, Z = 1; S, Z = 16). How many single bonds does it have?
(2)11.
Using the electronegativity values, find the nature of the bond in (a) lithium oxide, Li2O (b) sulphur dioxide, SO2. Show the working.
(2)12.
Aluminium (Z = 13) combines with sulphur (Z = 16). (a) Find the valency of each element from its electron configuration. (b) Write the formula of the compound by the criss-cross method.
(2)13.
(a) Common salt melts only at about 801 °C. Why do ionic compounds have very high melting points? (b) Naphthalene balls kept in a cupboard slowly become smaller and disappear. Naphthalene is a covalent compound. Which property of covalent compounds does this show?
(2)SECTION CAnswer all · 4 × 3 = 12 marks
14.
Calcium (Z = 20) and chlorine (Z = 17) form calcium chloride. (a) Write the electron configurations of calcium and chlorine.
(b) Draw the electron dot diagram to show the formation of calcium chloride.
(c) How many electrons and protons are there in the calcium ion? What is its charge?
(3)(b) Draw the electron dot diagram to show the formation of calcium chloride.
(c) How many electrons and protons are there in the calcium ion? What is its charge?
15.
Carbon dioxide (CO2) is a covalent compound (C, Z = 6; O, Z = 8). (a) Draw the electron dot diagram of a CO2 molecule.
(b) How many electron pairs does carbon share with each oxygen atom? Name this type of bond.
(c) Each C–O bond is polar (difference 0.89), yet the CO2 molecule is non-polar. Why?
(3)(b) How many electron pairs does carbon share with each oxygen atom? Name this type of bond.
(c) Each C–O bond is polar (difference 0.89), yet the CO2 molecule is non-polar. Why?
16.
Complete the table.
(3)| Positive ion | Negative ion | Formula of the salt | Name |
|---|---|---|---|
| K+ | SO42− | (i) …… | potassium sulphate |
| Al3+ | SO42− | (ii) …… | aluminium sulphate |
| Mg2+ | CO32− | (iii) …… | magnesium carbonate |
| Al3+ | PO43− | (iv) …… | aluminium phosphate |
| (v) …… | CO32− | (NH4)2CO3 | ammonium carbonate |
| Na+ | (vi) …… | Na3PO4 | sodium phosphate |
17.
(a) From H2O, Cl2, NH3, CO2 and HCl, pick out the polar molecules.
(b) Find the electronegativity difference of the N–H bond. Draw the bond showing the partial charges δ+ and δ−.
(c) Ammonia molecules are held to one another and to water molecules by hydrogen bonds. What is hydrogen bonding?
(3)(b) Find the electronegativity difference of the N–H bond. Draw the bond showing the partial charges δ+ and δ−.
(c) Ammonia molecules are held to one another and to water molecules by hydrogen bonds. What is hydrogen bonding?
SECTION DAnswer all · 2 × 5 = 10 marks
18.
The atomic numbers of five elements are given. The letters are not their real symbols: A = 3, D = 7, E = 9, G = 18, J = 20. Electronegativity: A 0.98, D 3.04, E 3.98.
(a) Write the electron configurations of all five. Which of them does not usually form compounds? Why?
(b) Which element forms a positive ion by losing two electrons? Write the equation.
(c) Write the formula of the compound formed by J and D.
(d) Draw the electron dot diagram for the formation of the compound of A and E. What type of bond is formed?
(e) Find the nature of the bond in DE3. Which atom carries the partial negative charge?
(5)(a) Write the electron configurations of all five. Which of them does not usually form compounds? Why?
(b) Which element forms a positive ion by losing two electrons? Write the equation.
(c) Write the formula of the compound formed by J and D.
(d) Draw the electron dot diagram for the formation of the compound of A and E. What type of bond is formed?
(e) Find the nature of the bond in DE3. Which atom carries the partial negative charge?
19.
Read the passage and answer the questions.
(b) Potassium (Z = 19) and chlorine (Z = 17) form potassium chloride. Write the equations for the formation of its ions.
(c) Using the electronegativity values, show that potassium chloride is ionic and that the C–H bonds in glucose are covalent. Why does the glucose solution not light the bulb?
(d) Common salt dissolves in water but not in coconut oil, while grease dissolves in kerosene. Explain.
(e) Water is called the universal solvent. Which feature of the water molecule helps it to dissolve salt? Draw a water molecule showing δ+ and δ−.
(5)During the monsoon, the health worker at a primary health centre in Alappuzha shows how to make ORS (ഒ.ആർ.എസ്. – oral rehydration solution): one packet, containing common salt (sodium chloride), glucose and potassium chloride, is dissolved in one litre of boiled and cooled water. At the school science club, Anu dips the two electrodes of a simple circuit (two torch cells and a small bulb) into the ORS solution, a glucose solution and coconut oil, and then presses them against dry crystals of common salt. Only the ORS solution lights the bulb. At home her mother removes a grease stain from a shirt with a little kerosene.
(a) Why does the ORS solution conduct electricity but the dry salt crystals do not?(b) Potassium (Z = 19) and chlorine (Z = 17) form potassium chloride. Write the equations for the formation of its ions.
(c) Using the electronegativity values, show that potassium chloride is ionic and that the C–H bonds in glucose are covalent. Why does the glucose solution not light the bulb?
(d) Common salt dissolves in water but not in coconut oil, while grease dissolves in kerosene. Explain.
(e) Water is called the universal solvent. Which feature of the water molecule helps it to dissolve salt? Draw a water molecule showing δ+ and δ−.
*** End of the question paper ***