<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:
.....(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](https://tex.z-dn.net/?f=%5Ctext%7BMoles%20of%20calcium%20oxalate%7D%3D%5Cfrac%7B0.429g%7D%7B128.1g%2Fmol%7D%3D0.0033mol)
The given chemical equation follows:
![Na_2C_2O_4(aq.)+Ca^{2+}(aq.)\rightarrow CaC_2O_4(s)+2Na^+(aq.)](https://tex.z-dn.net/?f=Na_2C_2O_4%28aq.%29%2BCa%5E%7B2%2B%7D%28aq.%29%5Crightarrow%20CaC_2O_4%28s%29%2B2Na%5E%2B%28aq.%29)
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
- 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](https://tex.z-dn.net/?f=0.0033mol%3D%5Cfrac%7B%5Ctext%7BMass%20of%20calcium%20ions%7D%7D%7B40g%2Fmol%7D%5C%5C%5C%5C%5Ctext%7BMass%20of%20calcium%20ions%7D%3D%280.0033mol%5Ctimes%2040g%2Fmol%29%3D0.132g)
- 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](https://tex.z-dn.net/?f=%5Ctext%7BMass%20percent%20of%20calcium%20ions%7D%3D%5Cfrac%7B%5Ctext%7BMass%20of%20calcium%20ions%7D%7D%7B%5Ctext%7BMass%20of%20milk%7D%7D%5Ctimes%20100)
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\%](https://tex.z-dn.net/?f=%5Ctext%7BMass%20percent%20of%20calcium%20ions%7D%3D%5Cfrac%7B0.132g%7D%7B125g%7D%5Ctimes%20100%3D0.107%5C%25)
Hence, the mass percent of calcium in milk is 0.107 %