Question

The nitrates of beryllium, calcium, magnesium, and strontium all decompose in the same way
when heated. When 2.00 g of one of these anhydrous nitrates is decomposed, 1.32 g of gas is
produced.
What is the nitrate?
A beryllium nitrate
B calcium nitrate
C magnesium nitrate
D strontium nitrate

Answer 1

These are all group 2 elements. Their nitrates will decompose to the oxide, nitrogen dioxide and oxygen

This will happen: (replace the X with Be, Ca, Mg, Sr)
\(\large\sf 2X(NO_3)_2(s)\to 2XO(s)+4NO_2(g)+O_2(g)\)

So for beryllium:
\(\to\sf 2Be(NO_3)_2 ~\to 2BeO ~+ 4NO_2 + O_2\)
Calcium:
\(\to\sf 2Ca(NO_3)_2 ~\to 2CaO ~+ 4NO_2 + O_2\)
Magnesium:
\(\to\sf 2Mg(NO_3)_2 \to 2MgO + 4NO_2 + O_2\)
Strontium:
\(\to\sf 2Sr(NO_3)_2 ~~\to 2SrO ~~+ 4NO_2 + O_2\)

I'll give you an example (it's not the correct answer but a way you can get to the answer)
Magnesiumnitrate has a molecular weight of 148.30 g/mol. You can use the ratio to calculate the amount of gas produced. 2 moles of \(\sf 2Mg(NO_3)_2\) will produce 4 moles \(\sf NO_2\) and 1 mole \(\sf O_2\).

So you have 2 grams of berylliumnitrate.
First thing you do is calculate how many moles that is. To do that you divide by molecular weight. So \(\sf \frac{2}{148.3}\) =0.01348 moles of magnesiumnitrate.

So the ratio is 2 \(\to\) 4 :1
when 2 = 0.01348, you double that to get the 4, so you have 0.02697 mol \(\sf NO_2\).
To get the 1 you halve it. so 0.0067425g \(\sf O_2\)

The molecular weight of \(\sf NO_2\) = 46 g/mol
MW of \(\sf O_2\) is 32 g/mool
To get the grams you multiply with the amount of moles.
So for \(\sf NO_2 \to\) 0.02697*46= 1.24062 gram nitrogen dioxide
for \(\sf O_2\) 0.0067425*32 = 0.21576 gram oxygen

Together thats 1.24062+0.21576 = 1.45638 gram gas

So now you know that C is not the answer.
Do this for A, B & D and you'll find out the correct answer
(you can find molecular weights on http://ptable.com)

\(\overline{\underline{\LARGE{\color{gold}{\star~}}\Large\tt\color{green}{I\;Hope\;this\;Helps!}\LARGE{\color{gold}{~\star}}}}\)

Answer 2

link: http://ptable.com (other one has a parenthesis included :P)

Answer 3

And sorry i said berylliumnitrate in the 5th part. supposed to be magnesiumnitrate \(\Huge\ddot\smile\)

Answer 4

thankyou :)