Question

How many moles of potassium are contained in 449 g of
potassium?
pls help im so lost

Answer 1

449 (g K) / 39.1 (g/mol K) = 11.5 mol K

Step-by-step explanation:

Potassium has atomic number 39.1

amount of K in 449g sample = 449/39.1 = 11.5 mol

Answer 2

`\boxed {\boxed {\sf 11.5 \ mol \ K}}`

Step-by-step 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.

• K: 39.0983 g/mol

We will convert using dimensional analysis, so we set up a ratio using the molar mass.

`\frac { 39.0983 \ g \ K }{ 1 \ mol \ K}`

We are converting 449 grams of potassium to moles, so we multiply by this value.

`449 \ g \ K *\frac { 39.0983 \ g \ K }{ 1 \ mol \ K}`

Flip the ratio. It is still the same value, but the units of grams of potassium cancel.

`449 \ g \ K *\frac {1 \ mol \ K}{ 39.0983 \ g \ K }`

`449 *\frac {1 \ mol \ K}{ 39.0983}`

`\frac {449}{ 39.0983} \ mol \ K`

`11.48387526 \ mol \ K`

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.

`11.5 \ mol \ K`

449 grams of potassium contains approximately 11.5 moles of potassium