CLASS 1X-CHEMISTRY
SAMPLE PAPER WITH SOLUTIONS
 1. Q. Write the charge  and mass of. an electron

2. Q. List three subatomic particles of an atom. Compare them on the basis of relative mass and charge in a tabular form.

3. Q. Find the number of electrons, protons and neutron possessed by the alpha particles used in the gold leaf experiment.

4. Q. Draw Bohr’s model for an atom with

(i) valency = 1,       (ii) number of orbits = 3       (iii) mass number =23.

Also identify the element. What conclusion can be drawn about the reactivity of the element?  

5. Q. (a) You are given an element. Find out     

(i) Number of protons, electrons and neutrons in ‘X’.   (ii) Valency of ‘X’.

(iii) Electronic Configuration of ‘X’.  

(b) If bromine atom is available in the form of, say two isotopes 35  (49.7%) and  (50.3%).Calculate the average atomic mass of bromine atom.  

6. Q. (a) From Rutherford’s a - particle scattering experiment give the experimental evidence for deriving the conclusion that

(i) Most of the space inside the atom is empty.  

(ii) Whole mass of an atom is concentrated in its centre.

(iii) The nucleus of an atom is positively charged.

(b) An element has mass number 31 and atomic number 15 find :

(i) the number of neutrons in the element, and

(ii) the number of electrons in the outermost shell.

7. Q. Give reasons:

(a) Mass number of an atom excludes the mass of an electron.

(b) Nucleus of an atom is charged.

(c) Alpha particle scattering experiment was possible by using gold foil only and not by foil of any other metal.

8. Q. Laws of conservation of mass is not fully applicable for: (a)Precipitation reaction            (b) Redox reaction      

(c) Nuclear reaction                  (d) Displacement reaction

9. Q. (a) Define the following terms with one example each. (i) Isotope (ii) Isobar

(b) Name the elements whose isotopes are used in:

(i) Nuclear Reactor (ii) treatment of cancer. (iii) Treatment of cancer

10.Q. State the problem of atomic structure which was solved after the discovery of neutron.

11.Q. (a) How many electrons are present in the valence shell of nitrogen, oxygen and argon?

(b) Nucleus of an atom has 5 protons and 6 neutrons. What is the atomic number, mass number and electronic configuration of the atom?

12.  The description of atomic particles of two elements X and Y is given below[3]

X Y Protons  8  8 neutrons 8 9 electrons 8 8

(i) What is the atomic number of Y?

(ii) What is the mass number of X?

(iii) What is the relation between X and Y?

(iv) Which element/elements do they represent?

(v) Write the electronic configuration of X?

(vi) Write the cation/anion formed by the element(i) Atomic number of y – 8

13. Which of the following are isotopes and which are isobars?

Argon, Protium, Calcium, Deuterium. Explain why the isotopes have similar chemical properties but they differ in physical properties?

14(i) Define mole

(ii) How is it related to Avogadro constant, relative mass and molecular mass?

(iii) What is the number of molecules in 0.25 moles of oxygen ? Avogadro’s no. = 6 .22 x1023.

OR

(i) Define atomicity

(ii) Give an example each of a polyatomic element and a polyatomic ion.

(iii) How many atoms are present in CaCl2 molecule and ion? SO4-2 Answers to the worksheet Ans:1 Particle       Symbol       Charge                        Mass Electron         e–                 -1.60×10-19 C          9.1×10-31  kg Ans: 2 Particle Symbol Charge Mass Electron e– -1.60×10-19 C 9.1×10-31  kg Proton p+  (H+) 1.60×10-19 C 1.672×10-27 kg Neutron n0 0.00 C 1.674×10-27 kg .Ans3: The number of electrons, protons and neutron are 0,2,2 Ans:4 Sodium has 11 protons and 12 neutrons. So, The mass number is 11 + 12  =  23. This element is metal and highly reactive Ans:5 (i) Number of protons, electrons and neutrons in ‘X’. are 7, 7 and 7 respectively      (ii) Valency of ‘X’. is = 3 [NH3] (iii) Electronic Configuration of ‘X’.  = 2, 5 (b) The average atomic mass of bromine atom =  +  = 80u Ans:6 (a)  (i) Most of the alpha particles passed through gold foil with getting deflected. (ii) Very few particles were deflected from their path by 1800 indicating that whole mass of the atom is present in its centre. (iii) Few particles deflected at small and large angle from their path indicating that centre is positively charged (b) (i) the number of neutrons in the element = 31-15 = 16 (ii) Electronic configuration 2,8,5  then the number of electrons in the outermost shell. = 5 ans:7 (a) Mass number is the sum of the number of proton and neutron present in nucleus of atom therefore Mass number of an atom excludes the mass of an electron. (b) Nucleus of an atom is charged as they contain positively charged proton. (c) This is because because gold has high malleability and can be hammered easily into thin sheet.      `  (a)Precipitation reaction            (b) Redox reaction       (c) Nuclear reaction                  (d) Displacement reaction Ans8: (c) Nuclear reaction   Ans9:(a) Isotopes are defined as the atoms of the same element, having the same atomic number but different mass numbers. For example, hydrogen atom, it has three atomic species, namely Protium, deuterium and tritium. The atomic number of each one is 1, but the mass number is 1, 2 and 3, respectively. Other such examples are carbon, C12, C14 and C16 where as chlorine, C35 and Cl37 Isobars. Atoms of different elements with different atomic numbers, which have the same mass number, are known as isobars. For example calcium, atomic number 20, and argon, atomic number 18 but the mass number of both these elements is 40. (b) (i)An isotope of uranium is used as a fuel in nuclear reactors. (ii) An isotope of cobalt is used in the treatment of cancer. (iii) An isotope of iodine is used in the treatment of goitre. Ans:10- (a) 5, 6 8 electrons are present in the valence shell of nitrogen, oxygen and argon respectively. (b) Nucleus of an atom has 5 protons and 6 neutrons. The atomic number = no of proton = 5, mass number = p + n = 5 + 6 = 11 This represents the element Boron Electronic configuration of the atom of Boron = 2,3 Ans:11 when the neutron was not discovered, many scientists found that the atomic mass of many atoms was found to be double or more than double the mass of total number of protons (as the mass of electron was so small that it was assumed to be negligible), so by the discovery of neutron led to the solution of this problem. For e.g.­ the mass of Carbon­ 12 atom is 12 u but the no. of protons were 6 so it becomes 6u. 12 (ii) Mass number of x – 16 (iii) x and y are isotopes (iv) x and y represent – oxygen (v) 168O - 2, 6 (vi) It will form an anion – O-2 13 Isobars – Argon and calcium Since isotopes have identical electronic configuration containing same number of valence electrons they have similar chemical properties. Since the masses are slightly different the physical properties (density, melting pt, boiling pt, etc) are different 14(i) Mole – one mole of any species (atoms, molecules, ions or particles) is that quantity in number having a mass equal to its atomic or molecular mass in   grams (ii) 1 mole = 6.022 x 1023 in number – Relative mass in g. (iii) 1 mole of oxygen contain 6.022 x 1023 molecules 0.25 mole of oxygen contain 6.022 x1023 x 0.25 = 1.505 x 1023 molecules OR (i) Atomicity – Number of atoms constituting a molecule (ii) Polyatomic element – sulphur Polyatomic ion – NH4-, OH-, SO4-2 (any one) (iii) Cacl2 – atomicity – 3 SO4-2 – atomicity - 5