Tartaric Acid Formula – Structure, Properties, Uses, Sample Questions

Tartaric acid comprises carbon, hydrogen, and oxygen with a molecular formula of C₄H₆O₆. The structure consists of two -COOH and two hydroxy groups. Tartaric acid is a naturally occurring diprotic, alpha hydroxycarboxylic acid found in citrus, bananas, tamarind, and especially grapes. It exists in 3 stereoisomeric forms meso tartaric acid, D-(-)-tartaric acid, and L-(+)-tartaric acid. It played an important role in bringing the concept of chirality into the light. Pasteur was the first one who modernized the concept of stereoisomerism in producing pure Levo tartaric acid through manual sorting of sodium ammonium tartrate crystals whereas, whereas Jean Baptiste Biot noticed the ability of tartaric acid in rotating the plane-polarized light. Its naturally occurring form is used as raw material in many organic syntheses. It is otherwise called as 2,3-Dihyroxysuccinic acid or dihydroxybutanedioic acid. Important derivatives of tartaric acid-like Rochelle salt are used as a mild laxative and diisopropyl tartarate a diester of tartaric acid as a catalyst in asymmetric synthesis.

Tartaric Acid Formula 

Tartaric acid is found naturally occurring in fruits. It is a white, crystalline organic acid. The formula for tartaric acid is C₄H₆O₆. Lets now understand how the structure looks like, the properties and uses of tartaric acid.

Structure of Tartaric Acid

Physical Properties of Tartaric Acid

Molar mass	150.08 g/mol
Physical appearance	white crystalline powder
Density	1.79 g/cm3
Solubility in water	0.21 kg/L
Melting point	206°C

Chemical Properties of Tartaric Acid

• Tartaric acid upon mild oxidation produces tartonic acid and when oxidized using a strong oxidizing agent gives oxalic acid.

• Reduction of tartaric acid with 2moles of HI yields succinic acid as a product

• Upon strong heating tartaric acid decomposes to form pyruvic acid with the evolution of CO₂

Uses of Tartaric Acid

• It plays a profuse role in the field of pharmaceutics
• It acts as a chelating agent with metals like magnesium and calcium
• Tartaric acid improves the taste of oral medication in combination with citric acid
• Used as a chelating agent in farming as it complexes with micronutrients in fertilizers used in soil
• It is used for cleaning metal surfaces
• It plays a vital role in wine fermentation in lowering the pH
• Its derivatives of it are also used in cough syrups
• Salt of tartaric acid-like potassium bitartrate is used in the fermentation process
• It also acts as an antioxidant
• Sodium bicarbonate in combination with tartaric acid is used as a leavening agent
• It is also used as a dye fixative, tanning leather, and in silvering mirrors

Sample Questions 

Question 1: Which stereoisomer of tartaric acid is optically inactive?

Answer:

Meso form is optically inactive since it possesses a plane of symmetry, due to internal compensation one half of the molecule was mutually canceled by the other half.

Question 2: In a racemic mixture of 50:50 D-(-) and L-(+) forms the optical rotation is 0°, Explain?

Answer:

D isomer rotates the plane polarised light towards the right, whereas L isomer towards left. Hence due to external compensation, there will be a mutual cancellation effect of two enantiomers making optical rotation zero.

Question 3: What is the role of tartaric acid in cake making?

Answer: 

Baking powder is a constituent of sodium bicarbonate and tartaric acid. On heating sodium bicarbonate forms sodium carbonate which reacts with tartaric acid to form sodium tartrate. So, in the absence of tartaric acid, the formed sodium carbonate adds a bitter taste to the cake.

Question 4: Tartaric acid reacts with NaOH in the following way

C₄H₆O₆ + 2 NaOH ⇢ Na₂C₄H₆O₆  + H₂O

Find the mass of tartaric acid in gm required for 33.32ml of 2N NaOH for titration to equivalence point?

Answer:

Mass of tartaric acid = 2 × 33.32 × 150.08 / 1000 × 2 

= 5 gm 

Question 5: How many stereoisomeric forms are possible for tartaric acid?

Answer:

The number of stereoisomers is calculated using the formula 2ⁿ, where n = no of chiral centers. In tartaric acid, as we have 2 chiral centers the possible stereoisomers are 4. Out of four, two stereoisomers are identical since they possess a plane of symmetry. Hence the possible stereoisomers are three.

Question 6: What happens if tartaric acid reacts with Fenton’s reagent?

Answer:

L-(+)tartaric acid can take part in various reactions. If L-(+)tartaric acid is treated with H₂O₂ in presence of ferrous salt i.e., Fenton’s reagent the acid undergoes oxidation to form dihydroxy maleic acid.

Question 7: What is Fenton’s reagent?

Answer:

It is a solution of hydrogen peroxide and ferrous salt generally FeSO₄. It is used as an analytical reagent, and catalyst in the oxidation of wastewater and contaminants. It can also be used to shatter certain organic compounds like tetra and trichloro ethylene.