Question

Calculate the number of moles in 17g of MgSO4​

Answer 1

Step-by-step explanation:

Number of moles = mass/molar mass

molar mass of MgSO4 = 24 +32+16(4)

= 120g/mol

number of moles=17/120

=0.141 moles

Answer 2

`\boxed {\boxed {\sf 0.14 \ mol \ MgSO_4}}`

Step-by-step explanation:

We are asked to find the number of moles in 17 grams of magnesium sulfate or MgSO₄.

We convert grams to moles using the molar mass. This is the mass of 1 mole of a substance. The values are found on the Periodic Table because they are equal to the atomic masses, but the units are grams per mole instead of atomic mass units.

Look up the molar masses of the individual elements: magnesium, sulfur, and oxygen.

• Mg: 24.305 g/mol
• S: 32.07 g/mol
• O: 15.999 g/mol

Notice the formula contains a subscript of 4 after the symbol O. There are 4 moles of oxygen in 1 mole of magnesium sulfate. We must multiply oxygen's molar mass by 4 before adding the other molar masses.

• O₄: 15.999 * 4 =63.996 g/mol
• MgSO₄: 24.305 + 32.07 + 63.996 = 120.371 g/mol

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

`\frac {120.371 \ g \ MgSO_4}{ 1 \ mol \ MgSO_4}`

We are converting 17 grams of magnesium sulfate to moles, so we multiply the ratio by this value.

`17 \ g \ MgSO_4 *\frac {120.371 \ g \ MgSO_4}{ 1 \ mol \ MgSO_4}`

Flip the ratio so the units of grams of magnesium sulfate cancel.

`17 \ g \ MgSO_4 *\frac{ 1 \ mol \ MgSO_4} {120.371 \ g \ MgSO_4}`

`17 *\frac{ 1 \ mol \ MgSO_4} {120.371 }`

`\frac{17} {120.371 } \ mol \ MgSO_4`

`0.1412300305 \ mol \ MgSO_4`

The original measurement of grams (17) has 2 significant figures, so our answer must have the same. For the number we calculated, that is the hundredth place. The 1 in the thousandth place tells us to leave the 4 in the hundredth place.

`0.14 \ mol \ MgSO_4`

17 grams of magnesium sulfate are equal to 0.14 moles of magnesium sulfate.