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olganol [36]
3 years ago
10

The amount ofcalcium present in milk can be determined by adding oxalate to asample and measuring the massof calcium oxalate pre

cipitated. 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%
Chemistry
1 answer:
Sauron [17]3 years ago
7 0

<u>Answer:</u> The mass percent of calcium in milk is 0.107 %

<u>Explanation:</u>

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

\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}      .....(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:

\text{Moles of calcium oxalate}=\frac{0.429g}{128.1g/mol}=0.0033mol

The given chemical equation follows:

Na_2C_2O_4(aq.)+Ca^{2+}(aq.)\rightarrow CaC_2O_4(s)+2Na^+(aq.)

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 = \frac{1}{1}\times 0.0033=0.0033mol of calcium ions

  • Now, calculating the mass of calcium ions by using equation 1, we get:

Moles of calcium ions = 0.0033 moles  

Molar mass of calcium ions = 40 g/mol

Putting values in equation 1, we get:

0.0033mol=\frac{\text{Mass of calcium ions}}{40g/mol}\\\\\text{Mass of calcium ions}=(0.0033mol\times 40g/mol)=0.132g

  • To calculate the mass percentage of calcium ions in milk, we use the equation:

\text{Mass percent of calcium ions}=\frac{\text{Mass of calcium ions}}{\text{Mass of milk}}\times 100

Mass of milk = 125 g

Mass of calcium ions = 0.132 g

Putting values in above equation, we get:

\text{Mass percent of calcium ions}=\frac{0.132g}{125g}\times 100=0.107\%

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

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