Compound X contains the same functional groups as citric acid. [Figure showing the skeletal structure of citric acid] The table describes some of the similarities and differences between citric acid and compound X. [Table with properties: chiral centre, reaction with Na, reaction with H+/Cr2O72- for citric acid and X]

1. (a)Complete the equation to show the reaction of excess sodium with citric acid. Show the skeletal structure of the product. [Equation with citric acid + ......Na → product][3]
2. (b)(i)Use the information in the table to deduce the skeletal formula of X, C3H6O3. Draw the skeletal formula of X in the box. Label the chiral centre of compound X with an asterisk (*).[2]
3. (b)(ii)Explain why compound X reacts with acidified Cr2O72– but citric acid does not.[2]
4. (c)Compound X is one of a pair of stereoisomers. Stereoisomerism occurs when a molecule has at least one of two key features. State the two key features that give rise to stereoisomerism. 1 2[2]
5. (d)A structural isomer of compound X does not fizz when added to sodium. Explain what is meant by structural isomer.[1]

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