RP 4 - inorganic

what is RP 4

carry out simple test tube reactions to identify cations and anions

cations

• group 2 ions

• NH4+

test for group 2 ions

NaOH

testing group 2 ions method

1. add BaCl2 to test tube

2. add NaOH, mixing well and recording observations

3. continue to add dropwise with gentle shaking until in XS. record observations

4. dispose by placing test tube in bowl of water

5. repeat with CaBr2, MgCl2 and SrCl2

when should you stop adding NaOH

test tube should not be more than half full

expected results

test for group 2 ions

dilute H2SO4

test for group 2 ions method

1. place drops of BaCl2 in test tube

2. add drops H2SO4 dropwise with gentle shaking until in excess. record observations

3. dispose in bowl of water

4. repeat with CaBr2, MgCl2, SrCl2

expected results

safety precautions

some barium salts are toxic so wear gloves

overall results for group 2

testing group 2 with flame test

1. dip nichrome wire in conc HCl and then sample

2. place in blue bunsen burner flame

3. record flame colour

results

• calcium 2+ = brick red

• barium 2+ = green

• strontium 2+ = red

test for NH4+

1. place drops NH3Cl into test tube

2. add drops NaOH and shake

3. warm gently with water bath

4. test fumes released using forceps to hold piece of damp red litmus paper in mouth of test tube

5. dispose by placing in a test tube full of boiling water

6. record observation of damp red litmus paper (turns blue)

what does shaking do

ensure reactant combine completely

whys water bath used

1. necessary as ammonia gas is very soluble

2. more gentle than using a flame

test for OH- (aqueous solution)

1. test 1cm depth of solution in test tube with red litmus paper or universal indicator paper

2. record observations (turns damp red litmus paper blue)

3. dispose test tube contents

test for OH- (ammonia, OH- form when it comes into contact with water)

1. place 5 drops ammonia solution on filter paper and place inside petri dish with lid

2. dampen piece of red litmus paper with distilled water and place on other side of petri dish

3. replace lid and observe for few mins

4. ammonia solution vapours will turn it blue

test for CO32-

1. add equal small volume of HCl to Na2CO3 in test tube

2. use delivery tube to transfer gas produced into a second test tube containing small volume of Ca(OH)2, aka limewater

3. put stopper into test tube containing limewater and shake

4. limewater will go cloudy if present as CO2 is produced

whys a bung used

prevents product loss

equations

test for SO42-

1. add equal volume of dilute HCl to BaCl2

2. BaSO4 formed (white ppt)

3. add small volume dilute HCl

4. as ppt does not dissolve, SO42- or HSO4- are present

equation

safety precautions

BaCl2 is harmful so wear gloves and lab coat

test for halide solutions

1. add small volume of HNO3 to KCl solution

2. add 2cm AgNO3 and record observations

3. swirl tubes and divide contents in half

4. one half - add XS dilute aq ammonia solution and record observations

5. one half - in fume cupboard add XS conc ammonia solution. record observations

6. repeat with KBr and KI in new test tubes

what does HNO3 (step 1) do

remove ions which may form different ppts

what does swirling do

ensures the ppt formed are evenly distributed

why is the solution separated into halves

allows further identification tests and initial ppts can be hard to distinguish

safety

• conc ammonia is corrosive - eye protection, gloves

• fume cupboard

• dilute HNO3 is an irritant

why does AGI not react with NH3

its too insoluble

group 7 results

test for halide ions (solid salts)

1. place small spatula of solid KCl in test tube in test tube rack

2. work in fume cupboard and add few drops conc H2SO4. record observations

3. test any gas evolved with moist blue litmus paper or universal indicator paper

4. repeat with solid KBr and KI recording observations

results

safety

• conc H2SO4 is corrosive

• gas produced are toxic and corrosive - carry out in a fume cupboard using small quantities of chemicals

• wear chemical splash proof eye protection and nitrile gloves

whys it not standard practice to react calcium and the higher group 2 metals with HCl

reaction would be too violent and dangerous