You are baking a cake for your friend\'s birthday and lost part of the recipe. Y

Question

You are baking a cake for your friend's birthday and lost part of the recipe. Your recipe calls for baking soda (NaHCO_3) and sour milk. Knowing that baking soda reacts with the lactic acid (CH_3CH(OH)COOH) write down the neutralization reaction that occurs. Assuming that you need half a teaspoon of baking soda (1tsp = 4.93cm^3) and enough sour milk to neutralize all the baking soda. The concentration of lactic acid in sour milk is 0.268 mol/L and the density of baking soda is 2.16 g/cm^3. How many cups of sour milk (1 cup = 236.6 mL) will you need to make your cake?

Explanation / Answer

The balanced equation is given below , baking soda is NaHCO3

a) CH3CH(OH)COOH (aq) + NaHCO3 (aq) ---> CH3CH(OH)COONa(aq) + H2O (l) + CO2 (g)

b) 1 tsp = 4.93 cm3

baking soda we have is 1/2 tsp = 4.93/2 = 2.465 cm3

Mass of baking soda = volume x density = 2.465 cm3 x 2.16 g/cm3

                    = 5.3244 g

Moles of NaHCO3 = mass/ Molar mass of NaHCO3

            = 5.3244 / 84 = 0.063386          ( 84g/mol is NahCO3 molar mass)

Now as per reaction lactic acid moles needed to neutralise all basking soda = 0.063386 moles

( since acid and baking soda react in 1:1 ratio)

given concetration of acid = 0.268 mol/L

Volume needed to get 0.063386 moles is given by moles/ Concentration

= 0.063386moles / 0.268 mol/L

= 0.2366 L = 236.6 ml

Thus we need 1 cup or milk   since 1 cup is 236.6 ml which is equal to our lactic acid solution volume

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