EAPSS Supporting Practical Science, D&T and Art
in schools and colleqes
Testing for carbonyl compounds with Tollen's reagent
Why do this?
Although both aldehydes and ketones contain the carbonyl functional group (-C=0), only aldehydes (or
reducing sugars) give a positive 'silver mirror test result with Tollen's reagent. This smal-scale test is a
useful qualitative analysis technique for detecting the presence of aldehydes (or reducing sugars).
Possible curriculum links: analysis, carbonyl compounds, aldehydes, ketones, sugars, redox.
This Practical Procedure draws on information from the following guidance.
Hozcords: 6, 87, 91A and as appropriate for the aldehyde/ketone or sugar being tested
Recipe Book: 6, 77 and 85
Suitability
Y12
Outline methodwith control measures (including PPE)
Wear eye protection. Ensure no Bunsen flames or other ignition sources (if aldehydes used).
Dispense aldehydes in a fume cupboard. Ensure laboratory is well-ventilated.
Ensure the test tube is scrupulously clean (or use a new one).
Make and use Tollen's reagent in situ only. Do not pre-prepare and store Tollen's reagent. Dispose of all
reaction mixtures immediately after use.
Do not scale up this method. An alternative procedure (involving a reducing sugar such as glucose) is used
for the demonstration-scale production of a silver mirror.
Procedure
1. Place 1 cm of0.1 M silver nitrate(V) solution in a clean test tube.
2. Add one drop of 0.4 M sodium hydroxide. A precipitate will form.
3. Add drops of 1 M ammonia solution until the precipitate just re-dissolves. The test tube now contains
Tollen's reagent. Use or dispose of it immediately.
4. Add 2-3 drops of the suspected aldehyde or a smal quantity of a reducing sugar.
• Use just enough solid sugar to cover the tip of a small spatula (see right).
Alternatively, usea solution of the reducing sugar (add 2-3 drops).
5 Stand the test tube with its contents in a 250 cm beaker that is half-filled with hot
water ( 60-70 °C, no hotter) from a kettle.
. Within a few minutes, asilver 'mirror' should formon the inner surface of the test tube.
6. Dispose of the reaction mixture immediately byrinsing down a foul-water drain.
Disposal Disposal notes:
Rinse the reaction mixture down a foul-wate Allow no longer than 30 minutes after carrying out
drain with a large volume of water. Do not the test before disposing of allreaction mixtures.
dispose of any reaction mixtures in a 'silver Explosive silver compounds form on standing and
residues' bottle. Rinse the test tubes. have been the cause of serious accidents in the
Cleaning the test-tubes (teacher/technician): past (see Bulletin 119).
rinsed tubes can be part-filled with 0.5 M nitric Tospeed up the cleaning process, start by standing
acid and left to stand overnight. Theycan then the test tubes (part-filled with 0.5 M nitric acid) in a
be rinsed out and washed as usual. beaker of hot water.
This docurment is intended to support teachers when planning poctical activities It is not designed as a worksheet for classroo
pp 0012 10/15 OHAPSs, Ihe Gardiner Building, Brunel Science Parh, Kingston lane, Uxbridge UB 3POQ
Page 1 of ? Tel: 01895 251496, Fax: 0189581432:f-nalt: uk;Web site: www.cleapss.org.uk
in schools and colleqes
Testing for carbonyl compounds with Tollen's reagent
Why do this?
Although both aldehydes and ketones contain the carbonyl functional group (-C=0), only aldehydes (or
reducing sugars) give a positive 'silver mirror test result with Tollen's reagent. This smal-scale test is a
useful qualitative analysis technique for detecting the presence of aldehydes (or reducing sugars).
Possible curriculum links: analysis, carbonyl compounds, aldehydes, ketones, sugars, redox.
This Practical Procedure draws on information from the following guidance.
Hozcords: 6, 87, 91A and as appropriate for the aldehyde/ketone or sugar being tested
Recipe Book: 6, 77 and 85
Suitability
Y12
Outline methodwith control measures (including PPE)
Wear eye protection. Ensure no Bunsen flames or other ignition sources (if aldehydes used).
Dispense aldehydes in a fume cupboard. Ensure laboratory is well-ventilated.
Ensure the test tube is scrupulously clean (or use a new one).
Make and use Tollen's reagent in situ only. Do not pre-prepare and store Tollen's reagent. Dispose of all
reaction mixtures immediately after use.
Do not scale up this method. An alternative procedure (involving a reducing sugar such as glucose) is used
for the demonstration-scale production of a silver mirror.
Procedure
1. Place 1 cm of0.1 M silver nitrate(V) solution in a clean test tube.
2. Add one drop of 0.4 M sodium hydroxide. A precipitate will form.
3. Add drops of 1 M ammonia solution until the precipitate just re-dissolves. The test tube now contains
Tollen's reagent. Use or dispose of it immediately.
4. Add 2-3 drops of the suspected aldehyde or a smal quantity of a reducing sugar.
• Use just enough solid sugar to cover the tip of a small spatula (see right).
Alternatively, usea solution of the reducing sugar (add 2-3 drops).
5 Stand the test tube with its contents in a 250 cm beaker that is half-filled with hot
water ( 60-70 °C, no hotter) from a kettle.
. Within a few minutes, asilver 'mirror' should formon the inner surface of the test tube.
6. Dispose of the reaction mixture immediately byrinsing down a foul-water drain.
Disposal Disposal notes:
Rinse the reaction mixture down a foul-wate Allow no longer than 30 minutes after carrying out
drain with a large volume of water. Do not the test before disposing of allreaction mixtures.
dispose of any reaction mixtures in a 'silver Explosive silver compounds form on standing and
residues' bottle. Rinse the test tubes. have been the cause of serious accidents in the
Cleaning the test-tubes (teacher/technician): past (see Bulletin 119).
rinsed tubes can be part-filled with 0.5 M nitric Tospeed up the cleaning process, start by standing
acid and left to stand overnight. Theycan then the test tubes (part-filled with 0.5 M nitric acid) in a
be rinsed out and washed as usual. beaker of hot water.
This docurment is intended to support teachers when planning poctical activities It is not designed as a worksheet for classroo
pp 0012 10/15 OHAPSs, Ihe Gardiner Building, Brunel Science Parh, Kingston lane, Uxbridge UB 3POQ
Page 1 of ? Tel: 01895 251496, Fax: 0189581432:f-nalt: uk;Web site: www.cleapss.org.uk
