Question

Carl makes the table below to determine the number of atoms of each element in the chemical formula 4Ca(ClO3)2.

A table with 3 columns and 2 rows. The first column labeled element has entries calcium, chlorine, oxygen. The second column labeled calculation has entries 1 times 4 , 1 times 2, 3 times 2. The third column labeled total atoms has entries 4, 2, 6.
What mistake did Carl make?

He did not multiply the calcium atoms by the subscript 2.
He did not add the coefficient 4 to the chlorine and oxygen atoms.
He did not add the subscript 2 to the calcium atoms.
He did not multiply the chlorine and oxygen atoms by the coefficient 4.



Which of these is a compound?

O
CO2
O2
Co



Elena makes the table below to determine the number of atoms of each element in the chemical formula 3(NH4)2SO4.

A table with 3 columns and 4 rows. The first column labeled element has entries nitrogen, hydrogen, sulfur, oxygen. The second column labeled calculation has entries 1 times 2 times 3 , 4 times 2 times 3, 1 times 4 times 3, 4 times 3. The third column labeled total atoms has entries 6, 24, 12, 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.


What does the chemical formula CaCl2 show about the compound it represents?

It is made up of one element.
It is made up of two elements.
It is made up of three elements.
It is made up of four elements.

Answer 1

1) Carl's mistake:
- Answer: He did not multiply the chlorine and oxygen atoms by the coefficient 4.
- Explanation: The coefficient 4 applies to the entire formula 4Ca(ClO3)2, so Cl and O counts inside the parentheses must be multiplied by 4 (Cl: 1×2×4 = 8, O: 3×2×4 = 24).

2) Which is a compound?
- Answer: CO2
- Explanation: CO2 contains two different elements (C and O) chemically bonded. O and O2 are elemental oxygen; Co is the element cobalt.

3) Elena's mistake:
- Answer: She should not have multiplied the sulfur atoms by the subscript 4.
- Explanation: SO4 gives S = 1 and O = 4; sulfur should be 1×3 = 3 (not multiplied by the oxygen subscript).

4) What does CaCl2 show?
- Answer: It is made up of two elements.
- Explanation: CaCl2 contains calcium and chlorine.