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Biomolecules CHM040 > Tests for Carbohydrates > Flashcards

Tests for Carbohydrates Flashcards

1
Q

The chemical tests employed to detect carbohydrates and to distinguish among them may be divided into two broad categories:

A
  1. tests based on production of furfural or a substituted furfural
  2. tests based on the reducing property of sugars
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2
Q

is a general test for carbohydrates

A

Molisch’s Test

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3
Q

In Molisch’s Test, compounds that are dehydrated by __ to form __ or __ will react with __ (in the Molisch’s reagent) to yield a __ condensation product. Although not a specific test for carbohydrates, a negative result is good evidence of the absence of carbohydrates.

A
  • concentrated H₂SO₄ (sulfuric acid)
  • furfural; hydroxymethyl furfural
  • alpha-naphthol
  • purple
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4
Q

a specific test for reducing sugars or the presence of free or potential aldehydes.

A

Benedict’s Test

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5
Q

In Benedict’s Test, a positive test is the appearance of a __ of __. However, the size of the particles may make it appear too __, __, or even __ if there is much deep blue cupric ion unreacted.

A
  • red-orange precipitate
  • Cu₂O (Copper(I) oxide)
  • orange; yellow; green
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6
Q

a test used to distinguish between monosaccharides and disaccharides

A

Barfoed’s Test

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7
Q

In Barfoed’s Test, a positive reaction may be only a little __ in the bottom of the test tube. If this appears within 2-3 minutes, it indicates a __; if it does not appear or show after 10 minutes, a __ is indicated.

A
  • dark red precipitate
  • monosaccharide
  • disaccharide
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8
Q

a specific test for ketoses

A

Selivanoff’s Test

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9
Q

This test is useful for distinguishing fructose (a ketohexose) from glucose, mannose, and galactose.

A

Seliwanoff’s Test

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10
Q

In Seliwanoff’s Test, the dehydration of __ with hot __ occurs much faster than the dehydration of the corresponding __. During the same time interval in which the dehydrated __ reacts with the __ (in Selivanoff’s reagent) to form a condensation product, the __ yields only a pale pink coloration.

A
  • ketohexoses
  • HCl
  • aldohexoses
  • ketohexose
  • resorcinol
  • aldohexose
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11
Q

a test for pentoses and nucleotides that contain the pentose sugar.

A

Bial’s Test

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12
Q

In Bial’s Test, it is based on the observation that __, which is formed from pentoses, yields a __ compound when treated with __ in the presence of __ (in the Bial’s reagent).

A
  • furfural
  • blue-green
  • orcinol
  • ferric ions
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13
Q

Bial’s Test is not specific for pentoses since other compounds such as __, __, and certain __ will produce blue or green products. __ (formed from hexoses) will give a yellow-brown coloration product.

A
  • hexoses
  • uronic acids
  • heptoses
  • Hydroxymethyl furfural
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14
Q

This test is positive with glucose and sucrose and negative for galactose and lactose. The most obvious sign of fermentation is the production of carbon dioxide.

A

Fermentation by Yeast

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15
Q

The most obvious sign of fermentation is the production of __.

A

carbon dioxide

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16
Q

Starch gives a blue color with iodine, and glycogen gives a reddish color with iodine. What test?

A

Iodine Test for Starch and Glycogen

17
Q

In the Iodine Test for Starch and Glycogen, starch gives a __ color with iodine, and glycogen gives a __ color with iodine.

A
  • blue
  • reddish
18
Q

Test solutions for tests for carbohydrates

A

1% glucose (dextrose)
1% sucrose
1% fructose
1% galactose
1% lactose
1% ribose
1%starch solution

19
Q

Test reagents for tests for carbohydrates

A
  • Molisch’s Reagent
  • Benidict’s Reagentt
  • Barfoed’s Reagent
  • Seliwanoff’s Reagent
  • Bial’s Reagent
  • Yeast
  • I2 and KI solution
  • Pentanol
20
Q

Procedure: Molisch’s Test

a. Place 2 mL portions of test solutions in separate test tubes.
b. Add 2 drops of __ into each and mix thoroughly.
c. Incline the tube and carefully add down the side of the tube 1 mL of __. A __ color should develop at the interface if carbohydrate-containing material is present.

A
  • Molisch’s reagent
  • concentrated H₂SO₄
  • purple
21
Q

Procedure: Benedict’s Test

a. Place 1 mL portions of the test solutions in separate test tubes.
b. Add 3 drops of __ into each and mix by swirling
c. Put all the test tubes simultaneously into a beaker half full of boiling water. Note which solution reacts __.

A
  • Benedict’s solution
  • first
22
Q

Procedure: Barfoed’s Test

a. Place 1 mL portions of test solutions in separate test tubes.
b. Add 3 mL __, mix, and place in a __ bath simultaneously for up to 10 minutes. Note which gives a __ first and record the time taken for the precipitate to form.

A
  • Barfoed’s reagent
  • boiling water
  • dark red precipitate
23
Q

Procedure: Saliwanoff’s Test

a. Place 2 mL portions of test solutions in separate test tubes.
b. Add 3 mL __ and place in a __ bath at the same time.
c. Record the time when a __ color appears in the clear solution (no precipitate). Compare colors at the same time. A __ or __ color is not a positive test.

A
  • Seliwanoff’s reagent
  • boiling water
  • dark red-brown
  • yellowish; apricot
24
Q

Procedure: Bial’s Test

a. Place 1 mL portions of test solutions in separate test tubes and add 3 mL of __.
b. Carefully heat the mixture until it boils, then let it cool. A __ color is a positive test for a pentose. If not easily recognized, add 1 mL of __ and shake. The green color will be extracted by the alcohol if a pentose is present. Note: Fructose and sucrose interfere in the test tube since they produce a __.

A
  • Bial’s reagent
  • bright
  • pentanol
  • brown color
25
Q

Procedure: Fermentation by Yeast

a. Weigh 0.2 g of __ and place it in a small test tube.
b. Half fill with test solution, close the end with a finger, and shake well.
c. When the solution and the yeast are well mixed, fill the test tube to the brim with test solution and cap it with a paper circle. It will be held by the pressure. Place the beaker on a water bath or in a warm place.

A
  • dry yeast
26
Q

Procedure: Iodine Test for start and glycogen

a. Place 1 mL of 1N __ and __ in separate test tubes.
b. Add a drop or two of __ in KI. Note the color produced. For better results with glycogen, place test tubes in __.

A
  • starch solution; glycogen
  • iodine
  • ice water

Biomolecules CHM040 (12 decks)

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