Sample of fish canned good " Sprat in tomato sauce " put in glass, weigh on technical weights to accuracy 0,01g, carry out it and wash off by hot distil water through a funnel, in measuring flask by capacity 250 sm3. Pour hot distil water up to 3/4 flask volume, well stir up and leave to stand on 30 mines. From time to time stir up the flask. After the expiration of the specified time cool flask under the crane with cold water, pour distil water up to a mark, close by a fuse and well mix contents of flask. Filter a liquid through the dry filter in a dry glass or flask.
Select by pipette 50 sm3 of filtrate in conic flask by capacity 200-250 sm3, add 3-5 drops 1% solution of phenolphthalein and titrate by a solution of caustic alkali of concentration 0,1 mol/ dm3.
For the painted solutions the end titration establish on the universal indicator.
Processing of results. Total acidity (.) considering on the appropriate acid, calculate under the formula:
Where V, - volume of a solution of alkali of concentration 0,1 mol/ dm3, spent on titrating, sm3;
- factor of recalculation in the appropriate acid:
For an apple acid - 0,0067;
For a citric acid - 0,064;
For an acetic acid - 0,0060;
For a dairy acid - 0,0090;
For a wine acid - 0,0075;
V - volume of filtrate taken for titrating (), sm3;
V - total volume of water in conic flask, poured to sample a fish, sm3;
m - weight of sample,g,.
Compare the received results to the requirements of the standard, make the conclusion about quality of canned good.
Test questions
- How is total acidity in canned goods with sour fillings normed?
- At what temperature is refraction coefficient for naphthalene monobromate defined?
- What is factor of recalculation for an apple acid?
Laboratory work #10.
Definition of calcium content in food products. Calcium and its compounds are constant components of mineral substances of meat and meat foods. Content of calcium and its compounds in meat depend on tissue structure of last. At that above 98% of its common content falls at lot bony tissue. Calcium is defined after dry or wet combustion by complex- metric titration using trilon and method, based on subsidence of calcium by ammonium oxalate.
Purpose of work: define calcium content in food products. In alkaline medium trilon forms with ions of calcium stable complex due to presence in own composition two free carboxyl groups. At titration of alkaline solution, containing ions of calcium, by solution oftrilonend point of titration fix by dint of metallochrome indicator Pointed indicators form complex with ions of calcium. Complexing is followed by decolorization of indicator. Addition to sample of versene leads to displacement of indicator from complex and decolorization of solution.
Method is founded on organic-matter degradation, solubilizing of mineralized substance in salt acid followed by volumetric determination of calcium by titration with versene in alkaline medium in the presence of metal indicator.
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Order of work.
Facility and ware: 1. crucible; 2. electric fire; 3. muffle furnace; 4. measuring flask on 50 ml; 5. pipettes on 5ml; 6. indicator paper; 7. cone flask on 100ml; 8. burette; 9. azotic acid high concent.., 25% salt acid, 2M sodium hydroxide, 0,01M trilon (versene), murexide, 0,01 M calcium nitrate.
Shot of researched product place in crucible, sample preliminary chark, heating it on a electric stove. After charring crucible place in muffle furnace and content burn by slow raise of temperature to 450-5000C till constant weight. Then crucible with white chark place on boiling water bath and for dissolution of chark bring in 5ml 25% spirit of salt. Gotten solution filter through ash-free filter in measuring flask capacity 50ml. Crucible and filter 2- 3 times wash by redistilled or deionized water, join rinse waters to filtrate. Contents of flask bring up mark by distilled water.
Aliquot part of chark solution place in cone flask capacity 100 ml and neutralize by indicator paper congo, adding drop by drop 2M solution of sodium hydroxide to pink coloration. Then in flask bring in on end of spatula indicator murexide, stick 2 ml 2M solution of sodium hydroxide and at once titrate by solution of versene to passage color indicator from pink to violet.
For improvement of versene concentration conduct control titration using 0,01 M nitrate solutions of calcium, derived from ficanal. To this in cone flask on 100 ml select 10 ml 0,01 M nitrate solutions of calcium and neutralize it by indicator paper congo, adding drop by drop 2M solution of sodium hydroxide and titrate by 0,01 M versene to passage pink coloration in violet.
Correction coefficient to solution of versene account by formula: K=V1/ V2, where: K- correction coefficient to solution of versene; V1-volume 0,01 M nitrate solutions of calcium, ml; V2-volume 0,01 M solution of versene, used on titration, ml. Calcium content determine by formula:=0,0004 V150100/mV2, where: Calcium content, %;
0,0004 Calcium quantity, equivalence to 1 ml 0,01 solution of versene, g;
Correction coefficient to solution of versene;
V1 volume of 0,01 versene, used to titrate, ml;
50 total volume of researched solution, ml;
m shot of product, g; V2 volume of solution, given for titration, ml
Test questions
- What does content of calcium and its compounds in meat depend on?
- Wh y does in alkaline medium trilon form with ions of calcium stable complex?
- What is thismethod founded on?
Rules of safety measures
On first practicum student must be acquainted with safety arrangements and running regime. In service in laboratory it is necessary to carry out follow:
- put on dressing grown
- control, all of necessary items are in place
- during runtime practicum it needs to observe silence
- avoid excessive walking, opening and closing of door
- in laboratory no smoke or meal
- shouldn't take out outside of chair, some kinds of materials (test-tubes, reagents)
- individual things it is necessary to head up assigned for that place
Every laboratory work takes shape in the form of report with short description of theoretic information, method of procedure, experimental results and conclusion. At the end of lessons student must set in order desk top, rub and take away apparatus, carefully wash hands and lay off dressing grown.
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Literature
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