Chemistry and Chemical Reactivity (9th Edition)

Number of moles of the base: $0.513\ M\times 29.1\ mL=14.93\ mmol$ If it's tartaric, number of moles: $0.956\ g\div 150.09\ g/mol=6.37\ mmol$ Ratio: $2.34$ If it's citric, number of moles: $0.956\ g\div 192.12\ g/mol=4.98\ mmol$ Ratio: $3.00$ Since the ratio is closer to the stoichiometric coefficient, it's citric acid.