If the prescribed dosage of milk of magnesia Mg(OH)2 is 3.5 moles, how many grams
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Answer:
Explanation:
To convert form grams to moles, the molar mass must be used. This is the mass (in grams) in 1 mole of a substance.
We can use the values on the Periodic Table. First, find the molar masses of the individual elements: carbon and oxygen.
- C: 12.011 g/mol
- O: 15.999 g/mol
Check for subscripts. The subscript of 2 after O means there are 2 oxygen atoms, so we have to multiply oxygen's molar mass by 2 before adding.
- O₂: 2* (15.999 g/mol)=31.998 g/mol
- CO₂: 12.011 g/mol + 31.998 g/mol =40.009 g/mol
Use the molar mass as a ratio.
Multiply by the given number of grams.
Flip the fraction so the grams of carbon dioxide cancel.
The original measurement of grams has 2 significant figures, so our answer must have the same. For the number we calculated, that is the thousandth place.
The ten thousandth place has a 5, so we round the 4 to a 5.
2.4 grams of carbon dioxide is about 0.055 moles.