a) What is carbohydrate?<br>b) How atmospheric $$\text{CO}_2$$ is transformed into carbohydrate in green plants? Indicate through chemical equation?<br>c) What is Tollen's test?<br>d) What is significance of Tollen's test in carbohydrates?<br>e) What chemical changes takes place during the test?<br>f) Glucose gives Tollen's test but not sucrose why?<br>g) What is oxidant in this reaction?<br>h) What is the formula of the red precipitate formed in Benedict's test conducted on carbohydrates?

PLACEHOLDER ANSWER - the question has eight written parts. a) Carbohydrates are polyhydroxy aldehydes or ketones, or compounds that give them on hydrolysis, often written $$\text{C}_x(\text{H}_2\text{O})_y$$. b) By photosynthesis in the presence of sunlight and chlorophyll, $$6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$$. c) Warming a compound with Tollens' reagent (ammoniacal silver nitrate) gives a silver mirror if the compound is a reducing agent such as an aldehyde. d) It distinguishes reducing sugars from non-reducing sugars. e) The sugar's aldehyde group is oxidised to a carboxylate and $$\text{Ag}^+$$ is reduced to silver, $$\text{RCHO} + 2[\text{Ag(NH}_3)_2]^+ + 3\text{OH}^- \rightarrow \text{RCOO}^- + 2\text{Ag} + 4\text{NH}_3 + 2\text{H}_2\text{O}$$. f) Glucose has a free aldehyde group (through its open-chain form), but in sucrose the glucose and fructose units are joined through both anomeric carbons, so no free aldehyde or ketone group is left. g) The oxidant is the diamminesilver(I) ion, $$[\text{Ag(NH}_3)_2]^+$$. h) The red precipitate is copper(I) oxide, $$\text{Cu}_2\text{O}$$.