Answer:
[tex]\boxed {\boxed {\sf 11.5 \ mol \ K}}[/tex]
Explanation:
We are asked to find how many moles of potassium are in 449 grams of potassium.
We will convert grams to moles using the molar mass. This is the mass of 1 mole of a substance. These values are found on the Periodic Table because they are the same as the atomic masses, but the units are grams per mole (g/mol) instead of atomic mass units (amu).
Look up potassium's molar mass.
We will convert using dimensional analysis, so we set up a ratio using the molar mass.
[tex]\frac { 39.0983 \ g \ K }{ 1 \ mol \ K}[/tex]
We are converting 449 grams of potassium to moles, so we multiply by this value.
[tex]449 \ g \ K *\frac { 39.0983 \ g \ K }{ 1 \ mol \ K}[/tex]
Flip the ratio. It is still the same value, but the units of grams of potassium cancel.
[tex]449 \ g \ K *\frac {1 \ mol \ K}{ 39.0983 \ g \ K }[/tex]
[tex]449 *\frac {1 \ mol \ K}{ 39.0983}[/tex]
[tex]\frac {449}{ 39.0983} \ mol \ K[/tex]
[tex]11.48387526 \ mol \ K[/tex]
The original measurement of grams (449) has 3 significant figures, so our answer must have the same. For the number we found, that is the tenths place. The 8 in the hundredth place tells us to round the 4 in the tenths place up to a 5.
[tex]11.5 \ mol \ K[/tex]
449 grams of potassium contains approximately 11.5 moles of potassium
