Counting Atoms Practice

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What is a chemical formula?

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A chemical formula is a way of expressing the composition of a substance using symbols for its constituent elements and numbers to indicate the quantity of each element.

Front

What does a subscript in a chemical formula indicate?

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A subscript indicates the number of atoms of the element that are present in a molecule. For example, in H2O, the '2' indicates there are 2 hydrogen atoms.

Front

What is a coefficient in a chemical formula?

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A coefficient is a number placed in front of a chemical formula to indicate how many molecules or moles of that substance are present. For example, in 2H2O, the '2' indicates there are 2 molecules of water.

Front

How many total atoms are in a molecule of C6H12O6?

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There are 24 total atoms in a molecule of C6H12O6 (6 Carbon + 12 Hydrogen + 6 Oxygen = 24).

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What is the difference between an element and a compound?

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An element is a pure substance made of only one type of atom, while a compound is a substance formed when two or more different types of atoms bond together.

Front

How many different elements are in the compound NaCl?

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There are 2 different elements in NaCl: Sodium (Na) and Chlorine (Cl).

Front

What is the significance of parentheses in a chemical formula?

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Parentheses in a chemical formula indicate that the atoms inside the parentheses are grouped together and may be multiplied by a subscript outside the parentheses. For example, in Ca(OH)2, the '2' applies to both O and H.

Front

How many oxygen atoms are in the formula 3Ca(OH)2?

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There are 6 oxygen atoms in 3Ca(OH)2 (3 x 2 = 6).

Front

What is the total number of potassium atoms in K2SO4?

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There are 2 potassium atoms in K2SO4.

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How do you determine the number of atoms of an element in a compound?

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To determine the number of atoms of an element in a compound, look at the subscripts in the chemical formula. If there is no subscript, it is understood to be 1.