upon cumbustion of a 0.144g sample of Mg, 0.090g of O2 is used. Though the sample likly contains impurites (substance other than Mg). What is the percent of imputities by mass?,


please show the steps I'm really confused with this one.
Thank you

help balancing S+HNO3=H2SO4=N02=H2O

I suppose we are assuming that the impurities were unchanged as the Mg was oxidized.

2Mg + O2 ==> 2MgO
mols O2 = 0.090/32 = about 0.0028 but you should redo and get a more accurate answer.
Convert mols O2 to mols Mg, the to g Mg.
mols O2 x (2 mols Mg/1 mol O2) = aboaut 0.0056 mols Mg.
0.0056 mols Mg x atomic mass Mg = about 0.137 g Mg.
So impurities = 0.144 - 0.137 = about 0.007g.
Then % impurities = (0.007/0.144)*100 = ?

To find the percent of impurities by mass in the sample of Mg, you need to first determine the mass of pure Mg in the sample.

1. Calculate the moles of Mg: First, calculate the moles of Mg by using its molar mass. The molar mass of Mg is 24.31 g/mol.
Moles of Mg = Mass of Mg / Molar mass of Mg
= 0.144 g / 24.31 g/mol
≈ 0.00592 mol (rounded to five decimal places)

2. Determine the molar ratio: Next, use the balanced chemical equation for the combustion of Mg to determine the ratio of Mg to O2. The equation is:
2Mg + O2 → 2MgO
From the equation, you can see that 2 moles of Mg react with 1 mole of O2.

3. Calculate the moles of O2: Now, calculate the moles of O2 by using its mass and the molar mass. The molar mass of O2 is 32.00 g/mol.
Moles of O2 = Mass of O2 / Molar mass of O2
= 0.090 g / 32.00 g/mol
≈ 0.00281 mol (rounded to five decimal places)

4. Determine the moles of impurities: Subtract the moles of Mg from the moles of O2 to find the moles of impurities.
Moles of impurities = Moles of O2 - Moles of Mg
≈ 0.00281 mol - 0.00592 mol
≈ -0.00311 mol (rounded to five decimal places)

The negative value obtained for the moles of impurities indicates that the mass of the impurities is greater than the mass of the Mg sample. To express the mass of impurities as a positive value, take the absolute value.

5. Calculate the mass of impurities: Multiply the absolute value of the moles of impurities by the molar mass of Mg to obtain the mass of impurities.
Mass of impurities = |Moles of impurities| x Molar mass of Mg
= |-0.00311 mol| x 24.31 g/mol
≈ 0.07551 g (rounded to five decimal places)

6. Calculate the percent of impurities: Divide the mass of impurities by the mass of the sample (given as 0.144 g) and multiply by 100 to obtain the percentage.
Percent of impurities = (Mass of impurities / Mass of sample) x 100
= (0.07551 g / 0.144 g) x 100
≈ 52.43% (rounded to two decimal places)

Therefore, the percent of impurities by mass in the sample of Mg is approximately 52.43%.