Trying to find milligrams

Question

How how many milligrams of calcium are in 1.37g of calcium carbonate

Answer 1

The easiest way to solve this problem is to convert 1.37 g of CaCO3 to moles, then to moles of Ca ion and then to grams/mg of Ca ion.

molar mass CaCO3 = 100 g/mol

1.37 g CaCO3 x 1 mol/100 g = 0.0137 moles CaCO3

moles Ca = 0.0137 moles CaCO3 x 1 mol Ca/mol CaCO3 = 0.0137 moles Ca

mass Ca = 0.0137 g Ca x 40.1 g Ca/mol Ca x 1000 mg/g = 549 mg Ca (to 3 sig. figs.)

Answer 2

Hi Joshua,

Grams and milligrams are both SI units for mass and follow standard conventions for prefixes of SI units. Commonly used prefixes for mass are:

Mega- (Metric Ton) - 1,000,000 grams

Kilo- 1000 grams

Milli- 1/1000 grams

To convert from one unit of mass to another, you will need to refer to their prefixes to find the correct conversion factor. Keep in mind the unit you're converting to should be on the top of the unit conversion fraction, with the unit converted from on the bottom so they cancel out. In your example, a gram is 1000 milligrams, so our unit conversion would be as follows:

1.37 g CaCO3 * 1000 mg/1 g = 1,370 mg CaCO3

We then need to take into account how much mass calcium has is in proportion to calcium carbonate. The chemical formula for calcium carbonate is CaCO3 which indicates there is 1 calcium per molecule of calcium carbonate. According to the periodic table, the mass of calcium is 40.078 g/mol, carbon is 12.011 g/mol, and 3 oxygens are 3*15.999 = 47.996 g/mol. Therefore, the percent mass of calcium in calcium carbonate would be the mass of calcium divided by the total mass:

40.078 g/mol calcium / (40.078 g/mol calcium + 12.011 g/mol carbon + 47.996 g/mol oxygen) = 0.40043962631 *100 = 40.043962631% calcium

Finally, we can multiply the percent calcium by our mass of CaCO3 in milligrams to find our answer.

40.043962631% of 1,370 mg CaCO3 = 548.602288055 mg Ca

I would also take into account the lowest significant figures used in our calculations (3 significant figures in 1.37 g) to end up with a final answer of:

549 mg Ca