The amount ofcalcium present in milk can be determined by adding oxalate to asample and measuring the massof calcium oxalate precipitated. what is the mass percent ofcalcium if 0.429 g of calcium oxalate forms in a125-g sample of milk when excess aqueous sodium oxalate isadded? na2c2o4(aq) +ca2+(aq) → cac2o4(s) +2na+(aq) a. 0.107% b. 0.202% c. 0.343% d. 1.10% e.1.37%

The mass percent of calcium in milk is 0.107 %

Explanation:

To calculate the number of moles, we use the equation:

     .....(1)

Given mass of calcium oxalate = 0.429 g

Molar mass of calcium oxalate = 128.1 g/mol

Putting values in equation 1, we get:

The given chemical equation follows:

Sodium oxalate is present in excess. So, it is considered as an excess reagent. And, calcium ion is a limiting reagent because it limits the formation of product.

By Stoichiometry of the reaction:

1 mole of calcium oxalate is produced from 1 mole of calcium ion

So, 0.0033 moles of calcium oxalate is produced from = of calcium ions

Moles of calcium ions = 0.0033 moles  

Molar mass of calcium ions = 40 g/mol

Putting values in equation 1, we get:

Mass of milk = 125 g

Mass of calcium ions = 0.132 g

Putting values in above equation, we get:

Hence, the mass percent of calcium in milk is 0.107 %

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