Xam Guide

Topics: Sulfuric acid, Acetic acid, Chlorine Pages: 10 (2521 words) Published: February 11, 2013
Here is cbse 2007 question paper of science:
Time allowed: 2 hours 15 mins; Maximum Marks: 100
General Instructions:|
1)| The question paper comprises of two sections A and B. You are to attempt both sections.| 2)| You are advised to attempt all the questions of Section A and Section B separately.| 3)| All questions are compulsory.|

4)| There is no overall choice. However, internal choice has been provided in some questions. You are to attempt only one option in such questions.| 5)| Marks allocated to every question are indicated against it.| 6)| Questions number 1-4 in Section A and 17, 18 in Section B are very short answer questions. These are to be answered in one word or one sentence.| 7)| Questions number 5-8 in Section A and 19, 20 in Section B are short answer questions. These are to be answered in 30 - 40 words each.| 8)| Questions number 9-14 in Section A and 21 - 23 in Section B are also short answer questions.These are to be answered in 40 - 50 words each.| 9)| Questions number 15, 16 in Section A and 24 in Section B are long answer questions. These are to be answered in 70 words each.| SECTION A

Question 1
1. What is the role of a catalyst in a chemical reaction?
A catalyst alters the rate of reaction without itself undergoing any change. Question 2
2. Which class of compounds gives a positive Fehling’s test ? Solution:
(out of syllabus)
Question 3
3. Approximately how many stars are there in the Milky Way ? Solution:
(out of syllabus)
Question 4
4. What is meant by the statement, “Potential difference between points A and B in an electric field is 1 volt.”? Solution:
Potential difference between points A and B in an electric field is said to be one volt when one joule of work is done in bringing a charge of 1 coulomb from point A to point B. Question 5
5. State the ‘Law of Chemical Equilibrium’. Write an expression for the equilibrium constant (K) for the reaction,  Solution:
(out of syllabus)
Question 6
6. Name the organic acid present in vinegar. Write a chemical equation which represents the commercial method for the preparation of this acid from ethanol. Solution:
The organic acid present in vinegar is acetic acid, .Acetic acid is be prepared by oxidizing ethanol.

Question 7
7. Distinguish between ‘artificial’ and ‘natural’ satellites. Why artificial satellites are called “eyes in the sky” ? Solution:
An artificial satellite is a man made object that continuously orbits Earth or some other body in space. A natural body which revolves around a planet is called natural satellite. Moon is a natural satellite of Earth. They are used to study the universe, help forecast the weather, assist in the navigation of ships and aircraft and support military activities hence known as “eyes in the sky”. Question 8

8. An electric lamp is marked 100 W, 220 V. It is used for 5 hours daily. Calculate

(i) its resistance while glowing.

(ii) energy consumed in kWh per day.
Given, P = 100 W, V = 220 V, t = 5 hours, R =? and E =?

By definition,
Substituting the values, we get, 

R = 484 ohms
Therefore, the resistance while glowing is 484 ohms.
The energy consumed can be determined as, 
Substituting the values, we get, 
Therefore, energy consumed in kWh per day is E = 0.5 kWh.
Question 9
9. (a) Write the chemical name and formula of bleaching powder.  (b) Why does bleaching powder smell of chlorine when exposed to air?  (c) Write chemical equation to represent the action of dilute hydrochloric acid on bleaching powder. Solution:

a) The chemical name of bleaching powder is calcium oxy-chloride and the formula is

b)Bleaching powder smells of chlorine when exposed to air since, it reacts with carbon dioxide of air and liberates chlorine.  
c) Bleaching powder reacts with hydrochloric acid, and forms calcium chloride, water and chlorine gas.

Question 10
10. What is...
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