Start with the recap, study the fully worked examples, then use the practice problems to
check your understanding of Mixture.
This page combines explanation, solved examples, and follow-up practice so you can move
from recognition to confident problem-solving in Chemistry.
Concept Recap
A physical combination of two or more substances that are not chemically bonded, retain their individual properties, exist in variable proportions, and can be separated by physical methods.
Things stirred together but not joined. Each substance keeps its own properties.
Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.
What to Focus On
Core idea:Mixture asks what the sample is, what property is being used, and whether a new substance is formed.
Common stuck point:Students often know a formula related to mixture but skip the recognition step: Am I classifying matter or using properties, state, particle behavior, or mixture evidence to describe a sample? That leads to a correct-looking substitution attached to the wrong chemical model.
Sense of Study hint:Ask: Am I classifying matter or using properties, state, particle behavior, or mixture evidence to describe a sample?
Worked Examples
Example 1
easy
Define a mixture and explain how it differs from a pure substance. Give two examples.Mixture (two species, physically combined) vs. pure substance (one species)
Answer
Mixture: variable composition, physically separable (e.g., salt water, air)
First step
1
A mixture is a combination of two or more substances that are physically combined but not chemically bonded.
Full solution
2
Unlike a pure substance, a mixture has variable composition — the proportions of components can change.
3
Examples: salt water (varying amounts of salt), air (varying amounts of water vapor). Both can be separated by physical methods.
Mixtures retain the properties of their individual components, while pure substances have fixed, characteristic properties. This distinction is fundamental to classifying all forms of matter.
Example 2
medium
A student has a clear, colorless liquid. Describe two experimental tests to determine whether it is a pure substance or a mixture.
Example 3
medium
A solution contains 20g of sugar dissolved in 80g of water. Find the mass percent of sugar and state whether it is a mixture or compound.
Example 4
medium
Show that adding 50g of pure water to 50g of a 10% salt solution still leaves a mixture, and compute the new salt percent.
Example 5
medium
60g of a salt-sand mixture is dissolved in water and filtered. The filtrate is evaporated to leave 24g of salt. What mass of sand remained on the filter, and what is the mass percent of salt in the original mixture?
Example 6
medium
You combine 5.0g of sulfur with 5.0g of iron filings. (a) Before heating, is the result a mixture or compound? (b) After heating until they react to form FeS, is it now a mixture or compound?
Example 7
hard
A 200g sample of brine is 15% salt by mass. You evaporate water until only 80g of solution remains. Assuming all salt stays, find the new percent salt.
Example 8
hard
Two beakers contain colorless liquids. Beaker A is 0.5M NaCl(aq); Beaker B is distilled water. Without tasting, propose two physical tests that distinguish them and justify each.
Example 9
hard
A 250g mixture contains 40g sand and 30g iron filings; the rest is salt. After magnet, dissolution, filtration, and evaporation, what mass should be recovered as salt?
Practice Problems
Try these problems on your own first, then open the solution to compare your method.
Example 1
medium
Explain why mixing iron filings and sulfur powder produces a mixture, but heating them together produces a compound (FeS). How could you distinguish between the two?
Example 2
hard
Seawater contains dissolved salts (∼3.5%), dissolved gases, and suspended particles. Classify seawater as a type of mixture and outline a procedure using at least three separation techniques to isolate the dissolved salt, fresh water, and suspended particles.
Example 3
easy
Is salt water an element, compound, or mixture?Salt water: two types of particles freely mixed — a mixture, not a compound
Example 4
easy
Can a mixture be separated by physical means? Give one example method.
Example 5
easy
Is a sample of pure copper (Cu) a mixture?
Example 6
easy
Do the substances in a mixture keep their own properties?
Example 7
easy
Is a mixture's composition fixed or variable?
Example 8
easy
Classify trail mix (nuts, raisins, chocolate) as a substance type.
Example 9
easy
Is air (nitrogen, oxygen, argon, etc.) a mixture?Air: multiple gas species sparsely mixed — a homogeneous gaseous mixture
Example 10
easy
Is salt water homogeneous or heterogeneous?
Example 11
medium
Both salt water and pure water look like clear liquids. How can you tell the mixture from the compound?
An alloy like bronze has a specific copper-tin proportion. Why is it still a mixture, not a compound?
Example 14
medium
How does separating a mixture differ from decomposing a compound, in terms of energy and method?
Example 15
medium
Sugar dissolves fully in water with no new substance formed. Mixture or compound, and which type?
Example 16
medium
Iron filings and sulfur powder are stirred together. Then the same amounts are heated until they react. Compound or mixture in each case?
Example 17
medium
Why can the components of a mixture be present in any ratio, unlike a compound?
Example 18
medium
Why does muddy water count as a heterogeneous mixture rather than homogeneous?Heterogeneous (muddy water, uneven) vs. homogeneous (salt water, uniform) liquid mixture
Example 19
medium
You have iron filings, salt, and sand mixed together. Outline a physical sequence to separate all three.
Example 20
challenge
A clear liquid is tested: it has a constant boiling point and cannot be separated by distillation into other liquids. Is it more likely a pure substance (element/compound) or a mixture?
Example 21
challenge
100 g of a homogeneous mixture is 30 g salt and 70 g water. After adding 30 g more water, what percent salt remains?
Example 22
challenge
Classify and order by separation difficulty: a sand-iron mixture, salt water, and water (a compound).
Example 23
easy
Classify a cup of black coffee (water with dissolved coffee solids) as element, compound, or mixture.
Example 24
easy
Is granite, which shows visible grains of quartz, feldspar, and mica, a homogeneous or heterogeneous mixture?
Example 25
easy
Classify fog (tiny water droplets suspended in air).
Example 26
easy
Steel is iron mixed with about 1% carbon. Is the iron's magnetic property preserved?
Example 27
medium
You need to separate a powder containing salt, sawdust, and iron filings. Outline a step-by-step physical procedure.
Example 28
medium
A clear liquid boils sharply at exactly 100∘C at 1atm and leaves no residue when evaporated. Mixture or pure substance?
Example 29
medium
You stir oil and vinegar together. The liquids form layers after standing. What kind of mixture is this?
Example 30
medium
A chemist wants the salt out of seawater but also wants to collect the fresh water. Which technique works best?
Example 31
medium
In ink chromatography, different colored dyes travel different distances on the paper. What property of mixtures does this demonstrate?
Example 32
hard
An unknown clear liquid is heated and the temperature is recorded as it boils. The temperature rises steadily from 78∘C to 100∘C as the liquid evaporates. Is it a pure substance or a mixture? Briefly justify.
Example 33
hard
A bottle of vinegar is labeled "5% acetic acid". Classify the contents and explain why the label states a percent rather than a chemical formula.
Example 34
hard
Air at sea level is roughly 78%N2, 21%O2, 0.9% Ar, and 0.04%CO2 by volume. Explain why this is a mixture and what would change if it were a compound instead.
Example 35
hard
A sealed tube containing NO2 and N2O4 in equilibrium looks brown. Is the visible content a mixture or compound, and why is the distinction subtle?
Example 36
hard
You add 5.0g of sand to 50g of water. Is the result a solution, suspension, or colloid? Justify briefly.
Example 37
challenge
A 500g alloy is 60% Cu, 30% Zn, 10% Sn by mass. You melt and add 200g more pure tin. Compute the new mass percent of each metal. Explain why this is still a mixture.