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A compound has the formula Mg3X2. If 1.87 g of X combines with 4.86 g of magnesium, what is the atomic weight of X?
A) 7.0
B) 14.0
C) 21.0
D) 28.0
E) 32.0
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I'm having a really rough time with this one. It seems the total weight is 6.73 g, and that 27.79% of the compound is X2 and 72.71% is Mg3. 4.86 g is also 0.20 mol of Mg3 I think (4.86 g / 24.31 g/mol = 0.20 mol) (or is it 4.86 g / 3 = 1.62 g, then 1.62 g / 24.31 g/mol = 0.067 mol ? Not sure.). Beyond that, I'm really lost as to what to do.
Thanks to anyone who can help.
I think you are on the verge but just need a push. Try this. Isn't 1.87 g X2 = 0.0667 mol X2? Isn't 6.73 g (0.0667 mol) Mg3X2? Check my thinking.
I wrote 3Mg + X2 ==> Mg3X2.
So if we have 0.2 mol Mg, then 1/3 of that is 0.0667 mol X2 as well as 1/3 of that for mol Mg3X2.
thanks i got b!!!!!
I did, too. Could that be N2?
To find the atomic weight of X, we first need to find the number of moles of X and magnesium in the compound.
Let's start by calculating the number of moles of magnesium (Mg). We can use the molar mass of magnesium (24.31 g/mol) to convert the mass of magnesium (4.86 g) to moles:
Number of moles of Mg = Mass of Mg / Molar mass of Mg
= 4.86 g / 24.31 g/mol
≈ 0.20 mol (rounded to two decimal places)
Now, let's determine the number of moles of X. We know that a total of 1.87 g of X and 4.86 g of Mg combine to form the compound Mg3X2. Therefore, the mass of X in the compound can be calculated by subtracting the mass of Mg from the total compound mass:
Mass of X = Total compound mass - Mass of Mg
= 1.87 g - 4.86 g
= -2.99 g (negative value indicates an error)
It seems there may be a calculation mistake, as the resulting mass of X is negative. It's essential to double-check the calculations or clarify the given values to proceed with the problem.