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katrin2010 [14]
3 years ago
10

Why glucose does not give positive result with iodine test but not starch?

Chemistry
2 answers:
kolbaska11 [484]3 years ago
5 0

Answer:

This is a physical test. A chemical test for starch is to add iodine solution (yellow/brown) and look for a colour change. In the presence of starch, iodine turns a blue/black colour. ... Benedict's reagent will give a positive test result for glucose but not for starch.

Explanation:

please give me brainlist and follow

Burka [1]3 years ago
5 0

Answer:Amylose in starch is responsible for the formation of a deep blue color in the presence of iodine. The iodine molecule slips inside of the amylose coil.

Explanation:This makes a linear triiodide ion complex with is soluble that slips into the coil of the starch causing an intense blue-black colo

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Zinc metal is added to a flask containing aqueous hydrochloric acid. The flask contains 0.400 mole of HCl. How much hydrogen gas
dusya [7]

Answer:

0.4 g of hydrogen gas would be produced.

1. 0.48 mole of HCl is needed to react completely with 15.5 g of zinc.

2. HCl is the limiting reactant.

3. 2.61 g of zinc is in excess

Explanation:

From the balanced equation of reaction:

Zn(s)+ 2HCl(aq) --> H_2(g) + ZnCl_2(aq)

1 mole of Zn requires 2 moles of HCl to produce 1 mole of hydrogen gas.

15.5 g of zinc = 15.5/65.3 = 0.24 moles of zinc.

0.24 moles Zn is supposed to require 0.24 x 2 moles HCl which is equivalent to 0.48 moles HCl.

But only 0.400 mole of HCl is present. <u>Hence, HCl is the limiting reagent</u>. <u>For complete reaction with 15.5 g of Zinc, 0.48 mole HCl would be needed.</u>

0.400 mole of HCl will require 0.2 mole of Zn for complete reaction. <u>This thus means that 0.24 - 02 = 0.04 mole of Zn is in excess.</u>

0.04 mole Zn = 0.04 x 65.3 = 2.61 g excess Zn.

Now, since HCl is the limiting reagent;

2 moles of HCl is required to produce 1 mole of H2 according to the equation.

0.400 mole HCl will therefore yield 0.400 x 1/2 = 0.2 mole H2

0.2 mole H2 = 2 x 0.2 = 0.4 g H2

<em>Hence, </em><em>0.4 g</em><em> of hydrogen gas would be produced.</em>

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Answer: 39.948 grams

Explanation:

The SI base unit for amount of substance is the mole. 1 mole is equal to 1 moles Argon, or 39.948 grams

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