A student added $10$ m/- $12$ m/ of Conc $H_{2} S O_{4}$ in a test tube containing $5$ g- $6$ g of sugar crystals and warmed it gently. He noticed that white crystals slowly turned brown and became a black mass. What happened in this change?

H_{2} S O_{4}

turned black but no change took place

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Sugar got charred by the action of hot. conc.

H_{2} S O_{4}

and a chemical change took place

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It is only a physical change

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It is an irreversible physical change

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Solution

The correct option is A $H_{2} S O_{4}$ turned black but no change took place
When the student added $10 - 12 m l$ of concentrated $H_{2} S O_{4}$ in the test but a tube of $5 - 6 g$ of sugar crystals and warms it gently, then the white crystals slowly turned brown and became a black mass. This is because concentrated $H_{2} S O_{4}$ acts as a dehydrating agent, so it removes water from sugar. Chemical formula of sugar is $C_{12} H_{22} O_{11}$ . So after dehydration from $H_{2} S O_{4}$ , only carbon is left behind, which gives it an appearance of a black mass

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Paheli’s mother made a concentrated sugar syrup by dissolving sugar in hot water. On cooling, crystals of sugar got separated. This indicates a:
(a) physical change that can be reversed
(b) chemical change that can be reversed
(c) physical change that cannot be reversed
(d) chemical change that cannot be reversed

Question 10

Two drops of dilute sulphuric acid were added to 1 g of copper sulphate powder and then small amount of hot water was added to dissolve it (step I). On cooling, beautiful blue coloured crystals got separated (step II). Step I and step II are:
(a) physical and chemical changes respectively
(b) chemical and physical changes respectively
(c) both physical change
(d) both chemical change

Q. Why sugar turns black in presence of conc.

H_{2} S O_{4} ?

Q. Sugar turns black on addition of conc.

H_{2} S O_{4}

. Why?

Q. Conc.

H_{2} S O_{4}

is added to a crystal of hydrated copper sulphate what happened?

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A student added 10m/-12m/ of Conc H2SO4 in a test tube containing 5g-6g of sugar crystals and warmed it gently. He noticed that white crystals slowly turned brown and became a black mass. What happened in this change?

A student added $10$ m/- $12$ m/ of Conc $H_{2} S O_{4}$ in a test tube containing $5$ g- $6$ g of sugar crystals and warmed it gently. He noticed that white crystals slowly turned brown and became a black mass. What happened in this change?