Exothermic reactions, acids, alkalis and making salts

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energy transfer in Reactions

AN EXOTHERMIC REACTION IS ONE WHICH TRANSFERS ENERGY TO THE SURROUNDINGS, USUALLY IN THE FORM OF HEAT AND USUALLY SHOWN BY A RISE IN TEMPERATURE

hand warmers

self heating cans

AN ENDOTHERMIC REACTION IS ONE WHICH TAKES IN ENERGY FROM THE SURROUNDINGS USUALLY IN THE FORM OF HEAT AND IS USUALLY SHOWN BY A FALL IN TEMPERATURE

sports injury packs

Reversible reactions can be ENDOTHERMIC and EXOTHERMIC

acids and alkalis

an acid is a substance with a PH of less than 7 acids from h+ ions in water

A Base is a substance with a PH of greater than 7

An alkali is a base that dissolves in water. Alkalis form OH- ions

H+ ions make solutions acidic

OH- ions make solutions alkaline

Formula for neutralisation :

acid + base > salt + water

can also be seen as H+ (aq) + OH- (aq) > H20 (I)

(s) - solid (I)- liquid (g)-gas (aq)- dissolved in water

Metal + Acid > Salt + Hydrogen

Hydrochloric Acid will produce Chloride salts

Sulfuric Acid will produce Sulfate salts

Nitric Acid will produce Nitrate Salts

metal oxides and metal hydroxides are bases

Making soluble salts

- add the base to the acid , the solid will dissolve in the acid as it reacts, excess solid will just sink to the bottom of the flask

- filter out the excess solid, to get the salt solution .

- in order to get pure, solid crystals of salt, evaporate some of the water and then leave the rest to evaporate slowly

Making soluble salts using an alkali

-add exactly the right amount of alkali to just netralise the acid, use an indicator to show when the reactions finished

- then repeat the method using exactly the same volumes of alkali and acid, so that the salt isn't contaminated

- evaporate off the water to crystallise the salt

Making insoluble salts - precipitation reactions

mix two solutions

once the salt has precipitated out, filter it from the solution , wash it, then dry it on filter paper

Precipitation can be used to remove poisonous ions ( lead) from drinking water etc

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