CHEM - 13. chemical tests (unfinished)

what is a precipitate

when 2 solutions are mixed and a solid is formed

test for hydrogen

place a lit splint to the gas and a squeaky pop will occur

test for oxygen

it will relight a glowing splint

test for carbon dioxide

bubble it through limewater, the limewater will go from clear to cloudy/milky

this is due to presence of calcium carbonate

test for chlorine gas

damp litmus paper will bleach

test for ammonia gas

damp red litmus paper will turn blue

test for carbonates

• add dilute acid

• test the gas/ bubbles using limewater

• clear to cloud/ milky if positive

test for halides

• add silver nitrate

• add a few drops of dilute nitric acid

• ….. precpitate is formed if positive

what are the halides and their ppt.

chloride - white ppt.

bromide - cream ppt.

iodide - yellow ppt.

test for sulphates

• add barium chloride

• add a few drops of hydrochloric acid

• positive = white ppt. (barium sulphate)

the 2 chemical tests for water

anhydrous copper sulphate

white - blue

colbalt chloride paper

blue - pink

2 physical tests for water (purity)

find its boiling point

100C

find its melting/ freezing point

0C

what would you see if acid was added to a solid carbonate

fizzing

what are halides

negative ions of group 7 elements

sodium hydroxide test

• add sodium hydroxide

• a coloured precipitate will form

state observations for each positive ion in the sodium hydroxide test

Copper (||) - blue ppt.

iron (||) - green ppt.

iron (|||) - brown ppt.

flame test method

• dip a nichrome wire in hydrochloric acid and heat in the roaring flame

• dip in hydrochloric acid again and then the substance to be tested

• heat the wire at the tip of the inner cone of a blue flame

positive results of flame test

lithium - red

sodium - yellow

potassium - lilac

calcium - brick red

copper - green

why do you dip the wire in hydrochloric acid, flame test

to sterilise the wire and to remove any residue that may affect the flame colour

why do you use a blue flame

to allow you to see the flame colour clearly

what is the test for ammonium

• add sodium hydroxide and warm

• test the gas given off with damp litmus paper

• if it turns blue its positive