11 multi-part examples, questions only
Pure substance or mixture - 20 single-part examples
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Example #1: Classify each example as either a pure substance (an element or a compound) or mixture (heterogeneous or homogeneous).
(a) table salt (b) aluminum (c) NaCl (d) magnesium (e) powdered orange drink (f) table sugar (g) tap water (h) gold (i) baking soda (j) chocolate chip cookie
(a) table salt
Table salt is 97 to 99% sodium chloride with a variety of other chemicals added in. Here is a brief discussion about chemicals added to table salt.
Be careful: in very rare instances, a teacher may require you to answer that table salt is a pure compound. That individual is operating under the misapprehension that table salt is 100% NaCl. It is not. If it happens to you, go with what the teacher wants.
Pure substance, specifically an element.
By the way, a sample of aluminum, no matter how pure, will always have a tiny bit of non-aluminum impurity. This is ignored when classifying aluminum as a pure substance.
Pure substance, specifically a chemical compound.
By the way, ALL chemical elements and compounds possess very small amounts of impurities. You should NOT use this to claim that there are no true pure substances.
Pure substance, specifically an element (sometimes the term 'chemical element' is used).(e) powdered orange drink
The powdered drink is mostly sugar, with a number of other chemicals for taste and to retard spoilage. Here is an example of the contents of this mixture.
(f) table sugar
Table sugar is about 99.7% sucrose (a chemical compound). I have not been able to find information on the composition of table sugar, so I can't really comment on what the other 0.3% is. I think it might be mostly glucose and/or fructose.
It may be that your teacher insists that table sugar is a pure substance because they believe it to be 100% sucrose (which is a legitimate chemical compound). I advise you to not question them on this point.
(g) tap water
Tap water is not pure water. It may have some residual chlorine from the water treatment plant. Also, tap water is treated so as to produce a pH of about 10. This protects underground water pipes (those made of iron) from corrosion.
Sometimes, tap water that has been improperly treated will have little bits of solid stuff. That makes it a heterogeneous mixture. However, that is fairly rare in these moden times of ours.
Remember, all chemical elements and chemical compounds (when not mixed with anything else) are considered to be pure substances.
(i) baking soda
Baking soda is 100% sodium bicarbonate, a chemical compound.
(j) chocolate chip cookie
Not all areas in the cookie are the same. Break off two different chunks, then compare them. They are different, which is the hallmark of a heterogeneous mixture.
You may eat the cookie now.
Example #2: Which of the following would best be described as a mixture? Is it heterogeneous or homogeneous?
(a) dry ice (b) table sugar (c) diamond (d) marble stone (e) liquid nitrogen (f) carbon
(a) dry ice ---> solid CO2, a chemical compound. It's a pure substance, not a mixture.
(b) table sugar ---> 100% sucrose, a chemical compound. It's a pure substance, not a mixture.
(c) diamond ---> solid carbon, but there are impurities. Heterogeneous mixture.
(d) marble stone ---> this is a mixture, a heterogeneous mixture to be specific.
(e) liquid nitrogen ---> N2 (liquid, gas, or solid) is a chemical element. It's a pure substance, not a mixture.
(f) carbon ---> all chemical compounds are pure substances. (Consider naturally-formed diamond, however, to be a heterogeneous mixture.)
You might think that diamond is a pure substance, but keep in mind that it is a substance formed in nature. During the formation process, impurities are included in random areas of the diamond crystal. Here is some more discussion on this topic.
I might also add that some teachers would consider diamond to be pure carbon, therefore identifying it as a pure substance. This is because ALL samples of elements or compounds contain impurities. As always, if your teacher differs from my answer, go with your teacher's answer.
Example #3: Identify each example as a compound, element, or mixture. For the latter choice, identify as homogeneous or heterogeneous
(a) silver (b) Gatorade (c) lead (d) sugar water (e) potassium iodide (f) tacos (g) apple pie (h) brass (i) bronze (j) hydrogen peroxide
Being that it is a chemical element, pure substance is the correct choice.
Gatorade is mostly water, but also contains sugar, sodium chloride, sodium citrate, and a number of other dissolved chemical compounds.
If what type of homogeneous mixture is asked, Gatorade would be considered a solution.
pure substance, specifically a chemical element.
Remnder: very tiny amounts of naturally-occurring impurities are ignored when making this determination.
(d) sugar water
homogeneous mixture, specifically a solution.
(e) potassium iodide
pure substance, specifically a chemical compound.
(g) apple pie
A very common wrong answer is to say brass is a pure substance. It is not.
A very common wrong answer is to say bronze is a pure substance. It is not.
(j) hydrogen peroxide
H2O2 is a chemical compound.
Example #4: Identify each example as a pure substance (compound or element) or a mixture. For the latter choice, identify as homogeneous or heterogeneous
(a) steam (b) gasoline (c) toothpaste (d) rubbing alcohol (e) pencil lead (f) iron block (g) dry ice (h) graphite (i) baking powder (j) copper wire
Steam is gaseous water and water is a chemical compound, no matter what physical state.
Gasoline is a complex mixture of about 150 chemical compounds. Some of these compounds were never removed in the distillation process to make gasoline, with many more added after distillation was completed.
A fairly large percentage of toothpaste are various insoluble solid compounds in power form. These act as abrasives to help clean the teeth. The presence of those abrasives is what makes toothpaste a heterogeneous mixture.
There are complexities in the formulation for toothpaste. This leads to different answers on the question of toothpaste being homogeneous or heterogeneous. If you wish to study this question more, Here is a search.
As always, go with what your teacher says is the correct answer.
(d) rubbing alcohol
homogeneous mixture. RA is 70% isopropyl alcohol and 30% water. By the way, the specific type of homogeneous mixture is that it is a solution.
(e) pencil lead
heterogeneous mixture of graphite and clay plus some minor ingredients.
Here's a search.
(f) iron block
Iron is a chemical element, so it's a pure substance
(g) dry ice
Dry ice is solid carbon dioxide, a chemical compound. It's a pure substance
Graphite is pure carbon, it is a chemical element. That makes it a pure substance.
By the way, diamond is also pure carbon as is buckminsterfullerene, making both of them also pure substances. However, I am ignoring the existence of color in diamonds, something that is caused by contaminates such as boron or nitrogen. Their presence would make the diamond be a mixture, probably homogeneous, but heterogeneous is also a possibility.
(i) baking powder
It is a mixture of baking soda (sodium hydrogen carbonate, cream of tartar (potassium hydrogen tartrate), and sometimes cornstarch.
Often, baking power and baking soda are called the wrong thing. Be careful on this one!
(j) copper wire
Copper is a chemical element, so pure substance is the correct answer.
It does not matter what the physical state (solid, liquid, gas) is.
Example #5: Identify as element, compound, heterogeneous mixture or homogeneous mixture
(a) unhomogenized whole milk (b) fat-free milk (c) Raisin Bran cereal with milk (d) homogenized whole milk (e) sour milk (f) Raisin Bran cereal without milk
(a) unhomogenized whole milk
Unhomogenized whole milk separates upon standing (which uses only gravity to separate), which is sufficient to identify it as a heterogeneous mixture. Here is some more information.
After most of the fat has separated out, there remains a certain amount of fat that will not separate out by the force of gravity. A centrifuge must be used. Here is a search.
The fact that the centrifuge separates out some solid material shows that the whole milk is still heterogeneous, even after the separation by standing.
(b) fat-free milk
All fat has been removed, leaving dissolved lactose, some protein, a very tiny amount of fat and other minor ingredients.
Fat-free milk does not separate on standing, which helps to show its homogeneous nature. Also, fat-free milk does not produce solid material upon centrifugation. This indicates its homogeneous nature.
Some components of fat-free milk (lactose, for example) form a solution while others (protein is an example) form a colloid.
(c) Raisin Bran cereal with milk
The ChemTeam loves his Raisin Bran for breakfast!
(d) homogenized whole milk
(e) sour milk
Here's the Wiki article on sour milk. You might want to look up buttermilk. It's a heterogeneous mixture too.
(f) Raisin Bran cereal without milk
Example #6: Identify as element, compound, heterogeneous mixture or homogeneous mixture
(a) Dr Pepper (b) neon gas (c) mercury in a barometer (d) vinegar and oil salad dressing (e) caffeine (f) chlorine gas (g) vegetable soup (h) salad (lettuce, tomatoes, croutons, ranch dressing)
(a) Dr Pepper would be considered a homogeneous mixture, if there were no bubbles present (such as the top to the bottle being attached or the drink has all the excess carbonation bubble away. If bubbles are being formed, it would be a heterogeneous mixture.
(b) Neon gas is a chemical element.
(c) Mercury in (or out of) a barometer is a chemical element.
(d) Vinegar and oil salad dressing is a heterogeneous mixture. Note that this salad dressing separates into an oil layer and a vinegar layer. Separation upon standing undisturbed is a characteristic of a heterogeneous mixture.
(e) Caffeine is a chemical compound.
(f) Chlorine gas is a chemical element.
(g) Vegetable soup is a heterogeneous mixture. All common soups would be considered heterogeneous mixtures.
(h) Salad is a heterogeneous mixture. You might want to look up the term 'mechanical mixture.'
Example #7: Identify as element, compound, heterogeneous mixture or homogeneous mixture
(a) rust (b) dirty water (c) blood (d) spaghetti sauce (e) ice (f) sandy water (g) mud (h) 14-karat gold chain (i) the Earth's atmosphere
(a) rust - is a chemical compound of iron and oxygen, named iron(III) oxide. Because of this, the most common answer teacher's accept is that rust is homogenous. However, some teachers will consider rust to be a heterogeneous mixture if it has formed in nature, such as rust on a car. Mixed into the iron(III) oxide are tiny bits of pure iron (and maybe even tiny chips of paint).
(b) dirty water - this is a heterogeneous mixture. When allowed to sit, dirt particles will settle out to the bottom. The remaining water can be centrifuged to move the rest of the dirt to the bottom of the container.
(c) blood is a hetergeneous mixture. The 'formed element' consists of red blood cells, white blood cells, and platlets. An ultracentrifuge is required to separate them from the blood plasma.
By the way, blood plasma is a true homogeneous mixture. It is a solution with several different solutes involved, but is still considered a solution.
(d) spaghetti sauce is a heterogeneous mixture. Try searching for Vince's spaghetti sauce recipe. The ChemTeam has many happy memories of dinners (and lunch) at Vince's Spaghetti in Ontario, CA.
(e) ice is simply water (ignore the tiny amounts of impurities). Pure water is a chemical compound.
(f) sandy water is a heterogeneous mixture and it will settle out upon standing undisturbed.
(g) mud is a heterogeneous mixture. One important point about heterogeneous mixtures is that they can be made in any proportion of the various components. You cannot do this with pure elements or pure compounds.
(h) 14-karat gold chain is a homogeneous mixture referred to an an alloy. The proper amounts of gold and the other components (usually silve) are melted and throughly stirred. The same percentages of god and silve are present no matter which part of the chain you test.
(i) the Earth's atmosphere is a heterogeneous mixture
The atmosphere contains suspended dust particles (generally called particulates) and suspended water (mist, fog, clouds, rain drops, snow). Also, the gases in the atmosphere (nitrogen, oxygen, water vapor, and carbon dioxide being the big 4) vary in composition from bottom to top.
Example #8: Identify the following as properties of mixtures, compounds, or elements.
(a) the components maintain their own properties (b) is difficult to separate (c) the smallest particle is called an atom (d) an example is osmium (e) the smallest particle is called a molecule (f) an example is water (g) can be homogeneous or heterogeneous (h) can be made in any proportion
(a) mixture. The components of a mixture are simply near each other. They are not chemically bonded as in, say, hydrogen and oxygen being chemically bonded in water.
(b) chemical compounds are diffcult to separate. The elements are chemically bonded to each other and require more energy to separate that do the components of a mixture. This search has a variety of answers that compare compounds and mixtures. (Your teacher may consider 'element' to be the correct answer. This gets into a discussion about the separation using chemical means or nuclear means. The ChemTeam will stop the discussion at this point.)
(c) "atom" is the term used for the smallest chemical component of an element.
(d) osmium is a chemical element.
(e) "molecule" is the term used for the smallest identifiable part of a chemical compound that reproduces the composition represented by the molecular formula.
(f) water is a chemical compound.
(g) mixture. Pure substances (element or compound) do not use the terms heterogeneous or homogeneous.
(h) mixture. Elements and compounds are characterized by the "Law of Definite Composition." For example, water is always H2O no matter where you find it or what source it come from.
Example #9: Identify as a homogeneous mixture, a heterogeneous mixture, or neither.
(a) glucose dissolved in water (b) coffee (c) salt water (d) brass (Cu + Zn) (e) oil and water mixture (f) book (g) argon gas (h) liquid mercury (i) hydrogen gas (j) tree (k) sawdust (ℓ) pure carbon
(a) glucose dissolved in water forms a homogeneous mixture called a solution.
(b) coffee is a homogeneous mixture called a solution. This assumes no coffee grounds floating about or foam on top of the coffee.
(c) salt water is also a solution. This assumes no particulate matter floating (or swimming!) in the salt water
(d) brass is a homogeneous mixture called an alloy. It is considered homogeneous because the solid copper and solid zinc have been melted and, in the liquid state, the two metals have been throughly mixed.
(e) oil and water is a heterogeneous mixture. Even when mixed, the water and the oil separate out into their own layers.
(f) a book is a heterogeneous mixture (mostly of paper and ink).
(g) chemical elements, such as argon, are not mixtures. Neither is the answer.
(h) chemical elements, such as mercury, are not mixtures. Neither is the answer.
(i) chemical elements, such as hydrogen, are not mixtures. Neither is the answer.
(j) a tree is a heterogeneous mixture.
(k) sawdust is a heterogeneous mixture.
(ℓ) chemical elements, such as pure carbon, are not mixtures. Neither is the answer.
Example #10: Identify each of these:
(a) vinegar and water (b) milk (c) oil and vinegar (d) gasoline (e) concrete (f) iron filings (g) blood (h) plastic wrap (i) sugar (j) pickle relish (k) fruit cocktail (ℓ) steel (m) granola bar (n) Jell-O® (o) chocolate chip cookie dough
as one (or more) of these:
(1) pure substance (2) mixture (3) compound (4) elements (5) atom (6) molecule
Also, identify any mixtures as homogeneous or heterogeneous.
(a) vinegar and water
Vinegar is, itself, a mixture of acetic acid and water. Mixing vinegar with water produces a homogeneous mixture called a solution.
We will assume homogenized milk is being considered. The answer is complex because milk is a mixture of at least two different types.
(i) Milk sugar (scientific name is lactose) is dissolved in the water that forms most of the milk, forming a homogeneous mixture called a solution.
(ii) the protein and fat in milk do not dissolve in the water. Instead, they form as tiny globules that are evenly dispersed throughout the water and (this is important) the globules do not settle out upon standing. What has been formed is a homogeneous mixture called a colloid. (III) You can follow up on milk via this search. (iv) The answer would be different if we assumed unhomogenized milk was present.
(c) oil and vinegar
A mixture. Specifically, a heterogeneous mixture.
Gasoline is mostly octane (C8H18), but there are present other chemicals.
These chemicals are dissolved in the octane, forming a homogeneous mixture called a solution.
Dry concrete is a mixture of Portland cement (itself a mixture), sand (also a mixture), and aggregate (crushed rock, also a mixture by itself).
Portland cement, sand, and aggregate are each heterogeneous mixtures. The dry concrete a heterogeneous mixture. Concrete which has had water added and then cured to hardness forms discrete mineral phases, making it also a heterogeneous mixture.
There is material online about wet Portland cement being a colloid. The ChemTeam advises that you check with your teacher as to the answer they feel is most correct.
(f) iron filings
Iron is an element, which is considered to be a pure substance. So, (1) and (4) from the list above.
Also, (5) should be included. An atom is the smallest bit of an element just as a molecule is the smallest division of a chemical compound.
Blood, like milk, is a complex of more than one type of mixture.
The formed element (red blood cells, white blood cells, and platlets) for a heterogeneous mixture with the blood plasma.
The blood plasma has stuff dissolved in it, forming a homogeneous mixture. Some of the stuff forms a solution and some (specifically, proteins) form a colloid.
(h) plastic wrap
Plastic wrap is a chemical compound, so (1), (3), and (6) apply. More information about the chemical composition of plastic wrap can be found here.
All sugars are chemical conpounds, so (1), (3), and (6) apply. The most common sugar is sucrose.
(j) pickle relish
Ketchup, mustard, onions, and pickle relish on a hot dog? Yes, please.
(k) fruit cocktail
Steel is a homogeneous mixture called an alloy. It is considered to be homogeneous because the various ingredients are all melted and then the mixture is thoroughly stirred before being allowed to harden.
Do NOT call steel a pure substance. While steel is mostly iron (with is a true pure substance), it has significant amounts of other substances (examples include carbon, manganese, and boron).
(m) granola bar
When Jell-O® is dry, it is a heterogeneous mixture of gelatin, sweetener (usually sugar), and food coloring.
When the Jell-O® is added to hot water, the Jell-O® dissolves and forms a type of colloid called a sol. When the Jell-O® cools and hardens, it forms a colloid called a gel. Sols and gels are both considered to be homogeneous mixtures.
Here are some additional answers about Jell-O®. The linked answers provide more detail than my answer.
(o) chocolate chip cookie dough
Example #11: Classify the following as solution, colloid or suspension.
(a) Glue (b) Milk (c) Mayonnaise (d) Fish sauce (e) Paint (f) Syrup (g) Blueberry jam (h) Rubbing alcohol
Glue is a colloid. Here is a search to help in pursuing more information.
Before formatting this question, the ChemTeam was not aware that glue was considered to be a colloid.
Some components of milk (lactose is one) are present as a solution, some (fats are proteins) are present as a colloid.
By the way, my answer just above is based on homogenized milk. If the milk was not homogenized, then it would be a solution (the lactose) and a suspension (chunks of butterfat in the unhomogenized milk).
Colloid. Here's some more information about this answer.
(d) Fish sauce
Fish sauce is a solution, with everything dissolved in water. A bit more fish sauce on my Pad Thai? Yes, please.
Paint is a suspension. Upon standing, the suspended solid settles out, which is why paint must be stirred before usage.
All syrups are solutions. By the way, you can understand syrup two ways: (1) what you put on your pancakes and (2) what you swallow for medicine.
Here's a search.
(g) Blueberry jam
Blueberry jam is a colloid, specifically a gel. All jams would be considered colloids.
Here is a search on this topic.
(h) Rubbing alcohol
Rubbing alcohol is a solution. It is 70% isopropyl alcohol and 30% water.
By the way, isopropyl alcohol and water are both compounds, so they would be pure substances.
Pure substance or mixture - 20 single-part examples
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