Exothermic reaction for std 8 to 10

To measure the change in chemical reactions and conclude whether the reaction is exothermic or endothermic.

AIM : To measure the change in chemical reactions and conclude whether the reaction is exothermic or endothermic.

THEORY : During the chemical reaction if the temperature increases the reaction is exothermic and if temperature decreases the reaction is endothermic.

APPARATUS : Conical flask, 250 ml. Beaker, Stand, Thermometer, Glass rod, measuring cylinder, stirrer.

MATERIAL : Dilute hydrochloric acid, Zinc metal, Solid ammonium chloride,

Exothermic reaction

Observation : 

(1) initial temperature of dilute hydrochloric acid 0 C.
(2) Temperature of the mixture when Zinc metal dissolves in hydrochloric acid = 0 C.
(3) Difference of temperature = 0 C.
(4) Give chemical reaction of Zinc metal with hydrochloric acid.

NOTE :

 (1) Similarly heat of neutralization in neutralization reaction between dilute hydrochloric acid and sodium hydroxide can be measured.
(2) The increase in temperature can be noted when dissolution of solid sodium hydroxide in water is carried out.

PRACTICAL USES

The combustion reactions of kerosene, 

Petrol, 

LPG are exothermic, 

therefore these substance are used as fuel.

more Video presentation:

Exothermic reaction animation video

Focal Length by an Image of far distance object for std 8 to 10

To determine the focal length of a convex lens by obtaining an image of a far distance object. 

AIM : To determine the focal length of a convex lens by obtaining an  image of a far distance object.

PRINCIPLE :  Rays parallel to the axis, after being refracted by a convex lens, are focused on the principal focus. Distance   between the optical centre and the principal focus is known as the focal length.

APPARATUS   :   Convex lens, Stand, Screen, Foot-rule, etc,.

Focal length of a  far distance object

Observation : Distance between the optical center of the lens and the image on the screen = Focal length of the lens  f =   cm...         

Practical uses : Convex lens of proper focal length are used in optical instruments like simple microscope, compound microscope, telescope, etc,. Also the method given here in the simplest way to estimate the focal length of a convex lens.