CHEMISTRY

Time: 2 hours Class X Max Mark: 50

Instructions: Questions number 1 to 5 carry 2 marks each and Question number 6 to 15carry 4 marks each.

1. Calculate the mass of Calcium that will contain the same number of atoms as arepresent in 3.2 gram of sulphur. [At. Mass of: S=32, Ca=40]

2. If the empirical formula of a compound is CH and it has a vapour density of 13, findthe molecular formula of the compound.

3. If 6 litres of hydrogen and 4 litres of chlorine are mixed and exploded and if water isadded to the gases formed, find the volume of the residual gas.

4. Give a chemical test to distinguish between the calcium nitrate solution and Zincnitrate solution.

5. Classify the following as oxidation and reduction reaction, also complete the reaction.a) Cu Cu2+ b) Fe3+ Fe2+ c) Cl- Cl

6. An element Z has atomic number 16. Answer the following questions on Z:i. State the period and group to which Z belongs.ii. Is Z a metal or a non-metal?

iii. State the formula between Z and hydrogeniv. What kind of a compound is this?

7. a) Oxygen oxidises ethyne to carbon dioxide and water as shown by the equation:2C2 H2 + 5O2 = 4CO2 + 2H2 O2

What volume of ethyne gas at STP is required to produce 8.4 dm3 of carbon dioxideat STP? [H = 1, C = 12, 0 = 16]b) A compound made up of two elements X and Y has an empirical formula Y. If theatomic weight of X is 10 and that of Y is 5 and the compound ha a vapour density 25,find its molecular formula.

8. a) A compound has the following percentage composition by mass:Carbon 54.55%, Hydrogen 9.09% and Oxygen 36.26%. Its vapour density is 44.Find the Empirical and Molecular formula of the compound.

(H = 1; C = 12; O = 16)(b) Give the electron dot structure of the following:

(i) NH3 (ii) CH4 (iii) H3O+

9. The following questions refer to the periodic table:a. Name the second last element of the period 3.b. How many elements are in the second period?c. Name the element which has the highest electron affinity.

d. Name the element which has the highest electro negativity.e. Name the element which may be placed on group 1 but is not a metal.

10. The equation for the action of heat on calcium nitrate is:2Ca(NO3)2 2CaO + 4 NO2 + O2

(i) How many moles of NO2 are produced when 1 mole of Ca(NO3)2 decomposes?(ii) What volume of O2 at S.T.P. will be produced on heating 65.6 g of Ca (NO3)2?(iii) Find out the mass of CaO formed when 65.6 g of Ca(NO3)2 is heated.(iv) Find out the mass of Ca(NO3)2, required to produce 5 moles of gaseous products.(v) Find out the mass of Ca(NO3)2 required to produce 44. 8 L of NO2 at S.T.P.

(Relative molecular mass of Ca(NO3)2 = 164 and of CaO = 56)11. Give appropriate reasons for the following statements:

a. Carbon tetrachloride does not conduct electricity.b. Ionisation potential of the elements increases across a period.c. Ionic compounds are soluble in water whereas covalent do not.

12. An atom X has 2, 8, 7 electrons in its shells. It combines with Y having 1 electron inits outermost shell.

a. What type of bond will be formed between X and Y.b. Write the chemical formula of the compound.c. Would it be soluble in Water?

13. A metal X normally used for making calorimeters is heated in abundant supply of airuntil a black coloured residue Y is obtained. This Y reacts with sulphuric acid to formblue coloured salt Z. When to this solution little of ammonium hydroxide was added paleblue precipitates of A are obtained. This A dissolves in excess of ammonium hydroxideto form a deep blue solution of B. Identify the metal X and write the equations for theformation of various compounds i.e. Y, Z, A and B.14. The metals of Group 2 from top to bottom are Be, Mg, Ca, Sr and Ba.

a) Which one of these elements forms ions most readily and why?b) State the common features in the electronic configuration of all these elements.

15 (i)What is lone pair of electrons?(ii) Draw an electron dot diagram of a hydronium ion and label the lone pair of electrons.(iii) Name a neutral covalent molecule which contains one lone pair electrons.