Question

elena makes the table below to determine the number of atoms of each element in the chemical formula 3(nh₄)₂so₄.
element calculation total atoms
nitrogen 1×2×3 6
hydrogen 4×2×3 24
sulfur 1×4×3 12
oxygen 4×3 12
what mistake did elena make?
she should not have multiplied the sulfur atoms by the subscript 4.
she should not have multiplied the nitrogen atoms by the subscript 2.
she should not have multiplied the oxygen atoms by the coefficient 3.
she should not have multiplied the hydrogen atoms by the coefficient 3.

Explanation:

Step1: Analyze the chemical formula $3(NH_4)_2SO_4$

In a chemical formula, the sub - scripts inside parentheses are multiplied by the sub - script outside the parentheses, and then by the coefficient in front of the parentheses.

Step2: Analyze nitrogen atoms

There is 1 nitrogen atom in $NH_4$, and since there is a sub - script 2 outside the parentheses and a coefficient 3 in front, the number of nitrogen atoms is $1\times2\times3 = 6$, which is correct.

Step3: Analyze hydrogen atoms

There are 4 hydrogen atoms in $NH_4$, with a sub - script 2 outside the parentheses and a coefficient 3 in front, so the number of hydrogen atoms is $4\times2\times3=24$, which is correct.

Step4: Analyze sulfur atoms

In the formula $3(NH_4)_2SO_4$, there is 1 sulfur atom in $SO_4$. The correct calculation for the number of sulfur atoms should be $1\times3$ (only multiplied by the coefficient 3 in front of the whole formula), not $1\times4\times3$. The 4 is the sub - script of oxygen and has nothing to do with sulfur atom count.

Step5: Analyze oxygen atoms

There are 4 oxygen atoms in $SO_4$, and with a coefficient 3 in front of the formula, the number of oxygen atoms is $4\times3 = 12$, which is correct.

Answer:

She should not have multiplied the sulfur atoms by the subscript 4.