Practice Molecule in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The smallest unit of a covalent substance, consisting of two or more atoms held together by chemical bonds (typically covalent), acting as a single distinct unit.

Atoms stuck together. Water (H2O\text{H}_2\text{O}) is one molecule with 3 atoms.

Showing a random 20 of 50 problems.

Example 1

easy
Does NaCl\text{NaCl} exist as discrete molecules?

Example 2

easy
Sucrose has the formula C12H22O11\text{C}_{12}\text{H}_{22}\text{O}_{11}. How many atoms are in one molecule of sucrose?

Example 3

easy
Is argon (Ar) found in air a molecule or a single atom?

Example 4

hard
Compare diamond and a sample of CO2\text{CO}_2. Both contain carbon. Which sample is composed of molecules?

Example 5

medium
A student sees P4\text{P}_4 as a label for white phosphorus. Is P4\text{P}_4 a molecule? Explain.

Example 6

easy
Define a molecule and explain the difference between a molecule of an element and a molecule of a compound.

Example 7

medium
Explain why O2\text{O}_2 and O3\text{O}_3 (ozone) are both molecules of the same element but have different properties.

Example 8

medium
How many atoms are in one molecule of C6H12O6\text{C}_6\text{H}_{12}\text{O}_6 (glucose)? How many molecules are in 1 mole of glucose?

Example 9

medium
Ammonia is NH3\text{NH}_3. How many atoms are in 3 molecules of ammonia?

Example 10

hard
A sample contains 1.20×10241.20 \times 10^{24} molecules of H2O\text{H}_2\text{O}. How many moles of water and how many total atoms are in the sample?

Example 11

hard
A label says 'one molecule of KOH\text{KOH}.' Is the label scientifically accurate? Justify.

Example 12

easy
What type of bond typically holds the atoms in a molecule together?

Example 13

challenge
Classify each sample as (i) a discrete molecule, (ii) a noble-gas atom, (iii) an ionic formula unit, or (iv) a network solid: S8\text{S}_8, CaF2\text{CaF}_2, SiO2\text{SiO}_2 (quartz), Kr.

Example 14

hard
Ethylene glycol is C2H6O2\text{C}_2\text{H}_6\text{O}_2. What is the total number of atoms in 0.400.40 mol of ethylene glycol?

Example 15

easy
How many atoms are in one molecule of carbon dioxide, CO2\text{CO}_2?

Example 16

medium
How many molecules are in 0.250.25 mol of CO2\text{CO}_2?

Example 17

medium
How many hydrogen atoms are in 5 molecules of ammonia, NH3\text{NH}_3?

Example 18

hard
A molecule of aspirin has the formula C9H8O4\text{C}_9\text{H}_8\text{O}_4. Calculate the total number of atoms in one molecule, the molar mass, and the number of hydrogen atoms in 0.500.50 mol of aspirin.

Example 19

easy
Is O2\text{O}_2 (oxygen gas) a molecule? Explain in one line.

Example 20

challenge
Classify each as molecular element, molecular compound, or neither: O2\text{O}_2, CO2\text{CO}_2, Ne, NaCl\text{NaCl}.
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