science chapter 11 - chemical changes

physcial change

no new substance formed

no change in properties

often reversible

chemical change

new substance formed

change in properties

not reversible

types of chemical changes

combustion

thermal decomposition

oxidation

blue litmus paper

turns red in acidic solution

changes colour at PH level 7

red litmus paper

turns blue in alkaline solution

changes colour at PH level 7

methyl orange

turn from orange to red in acidic solution

changes colour at PH 4

turn from orange to yellow in alkaline solution

screened methyl orange

turn from green to pink in acidic solution

changes at PH 4

thymolphthalein

turns from colourless to blue in alkaline solution

changes at PH 10

universal indicator

changes from green to red, orange or yellow in acidic solution

changes colour depending on PH level

changes from green to blue, indigo, violet in alkaline solution

Indicator

an indicator is a substance which changes colour depending on whether the solution being tested is acidic or alkaline

ph level

1-6 acidic

8-14 alkaline

features of acids

acids are corrosive

have sour taste

can conduct electricity

turns damp blue litmus paper red

displays acidic properties only if they are in water

acid + metal =

salt + hydrogen gas

acid +metal carbonate =

salt + water+ carbon dioxide gas

acid + alkaline =

salt + water

acid + ammonium =

salt + ammonia gas + water

test for hydrogen gas

put dilute hydrochloric acid into test tube

put magnesium ribbon in dilute hydrochloric acid

put burning splint into mouth of test tube

if there is a ‘pop’ sound, hydrochloric gas is present

alkali

it is a substance that turns damp red litmus paper blue

features of alkali

can conduct electricity

have bitter taste

have soapy feeling

turns damp red litmus paper bluete

test for ammonia gas

pour alkaline + ammonium salt solution in tube

place damp red litmus paper at the mouth of test tube

if colourless and pangent gas turns damp red litmus paper blue, ammonia gas is present