learn all about chemistry
Here is a key to the midterm review packet. Hope it helps!
1.Chemistry isthe study of matter and how it behaves.
2. What is a compound, and what are its properties? A compound is a substance that consists of at least two nonidentical atoms. This is a picky definition that means for example that O2 is a molecule but not a compound. Anyhow, compounds are substances, so they have specific properties- unique melting points, boiling points, reactivity, etc.
3. What is and is not matter? Matter is anything that has mass and takes up space. It would be enough to say that matter is anything that has mass were it not for the fact that there may be cases where something could have mass but not space (a black hole). There are lots of things that have neither mass nor space- ideas, motion, emotions, things like that.
4. Which of the following materials is a pure substance? Air, gasoline, steel, silver
air is not a pure substance, since it is a mixture of several substances including nitrogen, oxygen, etc.
gasoline is not a pure substance, since it is a mixture of hexane, octane, and other substances
steel is not a pure substance, since it contains iron, and small amounts of carbon, mangananese, etc
silver is a pure substance, and also an element
5. Compare mass and matter
Anything with mass is defined as matter. The only possible exception is a black hole (see #3). Most would agree that as the amount of mass increases the amount of matter increases, but that is not to say the number of particles increases, since ten hydrogen atoms has a lower mass than one uranium atom.
6. Chemical or physical change: rusting, melting, burning, fermenting, digesting, boiling, eating, dissolving, moving
chemical change: rusting, , burning, fermenting, digesting, , eating. All of these involve the formation of new substances.
physical change: melting, , dissolving, moving. None of these involve a chemical reaction.
7. Which can be decomposed by chemical means: molecules, cars, people, atoms, electrons
All except atoms and electrons can be decomposed chemically, since they contain more than one atom. An atom can be decomposed or “split” , but that is defined as a nuclear, not a chemical, process.
8. Chemical or physical property? rusting, weighing, color, sublimation
Rusting, also known as oxidation, is the only chemical property, though it is better defined as a chemical process. Weighing and subliming are physical processes, since no reaction takes place.Color or the lack of it is a physical property.
9. List some physical and chemical properties of water
Physcially, water boils at one hundred degrees Celsius and melts at zero degrees Celsius as long as the pressure is one atmosphere. It is a clear and colorless liquid, with no odor, and takes large amounts of energy to heat- it has one of the highest specific heats of all substances. Chemically, it can be decomposed into hydrogen and oxygen electrochemically, or catalytically. Water is nonflammable, and can serve as both an oxidizing agent (source of oxygen) and a reducing agent (source of hydrogen) under the right conditions.
10. When water boils, what’s in the bubbles?
Assuming pure water, only water vapor. In the real world, for the first few minutes any dissolved gases will come out first. Water is thermally stable, so any decomposition is unlikely.
11. What happens to matter during a chemical reaction?
The amount of it does not change…”matter is not created or destroyed in a chemical reaction”. New forms of matter, meaning new substances, will form, since that is the definition of a chemical reaction. Note that matter can be converted to energy but only by nuclear, not a chemical, process.
12. What happens when ten pounds of salt is mixed with ten pounds of water? Consider the volume and mass of the resulting solution.
The mass of the resulting mixture will be twenty pounds, regardless of how much of it dissolves. Many factors would come into play when predicting the volume of the resulting solution. Since a pound of water has a mass of 453.6 grams, ten pounds of water has a volume of 4.536 liters at room temperature and atmospheric pressure. Things change when the salt is added. The initial volume of salt is much less due to its relatively high density relative to water (2.16 g/mL). Once it is added, the salt molecules that do dissolve will separate into ions, and those ions may pack well in water, reducing the volume, or poorly, having the opposite effect. It's important to note that most of the salt will not dissolve at all. The solubility of salt in water at room temperature is only about 26%, so most of the salt would settle to the bottom of the solution (making it heterogeneous)…I would guess the volume would be about seven liters or so, but it is one of those things that is easy and precise to perform the experiment, and very iffy to predict.
"When dissolved in water, the sodium chloride framework disintegrates as the Na+ and Cl- ions become surrounded by the polar water molecules...Solutions of sodium chloride have very different properties from pure water. The freezing point is −21.12 °C for 23.31 wt% of salt, and the boiling point of saturated salt solution is near 108.7 °C.
Nothing chemically would happen if you mixed those two substances.Although dissolving might appear to be a chemical process since the ions separate, they recombine when the solute evaporates, so overall nothing changes. And most of it the salt would not even dissolve.
13. Be sure you are familiar with Material Safety Data Sheets.
There are some in my room- have a look. The idea is to “provide workers and emergency personnel with procedures for handling or working with that substance in a safe manner”, and to provide some chemical and physical property information. They are required in most situations where people need to know something about a chemical and quick
14. Why does it make sense to pour acid into water, rather than the reverse?
Short answer: acid into water creates an initially safe, dilute solution that can yhen be made more concentrated; and the water is an ideal heat sink. Adding water to acid does the opposite, with no effective way to absorb the energy produced in that violently exothermic reaction. Well, it was supposed to be a short answer...
Imagine one drop of water entering a beaker of concentrated sulfuric acid. There is no water in the acid to absorb the heat of that exothermic reaction, and the drop water, along with some of the acid, will boil almost instantly, with a tendency to spatter and to spray around anyone near…not good. When the first drop of acid hits a beaker of water, the amount of dilution is huge- you aren’t making a strong solution instantly. So there is plenty of water to absorb the heat produced. In summary, the dilution factors and solvent available both favor adding acid to water, rather than the reverse.
15. In what section of the laboratory report would you record all the measurements that you make?
I would put that in the data section. Now it’s boring if it is just a list or a table, so I would used those measurments to create a graph, so that the results can be interpolated (you can predict between data points) and extrapolated (one can predict beyond data points). I would be sure to include my units for these graphs.
16.In chemistry, it is usually not enough just to write the number that answers a question…what is missing?
The units are what make numbers meaningful.
16. How do you record the volume of a graduated cylinder precisely?
By estimating between the graduations. If the graduations show milliliters, for example, a resulting measurement should be say 26.4 mL- note how it is one level more precise than the graduations.
17. Which numbers are significant?
A mathematician would say all numbers matter, but for significant figures we can say that if it is not zero it is significant, and if it is “sandwiched” (between nonzero numbers), or if it iz a zero after a decimal place.
18. The number of significant figures in the measurement 170.0400 km
That would be all of them (7)
19. To two significant figures, the measurement 0.025g should be reported as
Well it would be ok to leave it just the way it is since it only has 2 sig figs, but you could also write it as 2.5 x 10-2 to emphasize it.
21.Three samples of 0.12g, 1.8g, and 0.56234g are mixed together. What is the total mass?
When you add them up you get 2.48234, and the rule for adding numbers is to report your answer with the same number of decimal places as the least precise answer. Since 1.8 is only accurate to the tenth, the answer is 2.5g; note that we had to round up.
- Using significant figures, what is the average of 3.00 + 2.00 + 4.00 + 7.00
Once again we are only adding. In this case every answer is accurate to the hundredth of a unit (and the units aren’t specified), so the answ.er is 16.00/4 = 4.00
- The dimensions of a rectangular solid are measured to be 1.27cm, 1.3cm, and 2.5cm.What is the volume?
I hope you know that the area is length x width x height. So we are multiplying, which means we report the answer using the fewest significant figures provided in the data, which is 2. The “raw answer” is 4.1275 cm3, so we round down to get our answer of 4.1 cm3.
- What is the density of 37.72g of matter whose volume is 7.80cm3?
Density = m/v, and we are given both. The density is 37.72g/7.80 cm3 = 4.84 g/cm3; note how we rounded up when providing the answer to three significant figures. Note how the units are worked out mathematically- grams divided by cubic centimeters = g/cm3.
- What are the resulting UNITS for the calculation (19.3g/cm3)x10 cm3x(1mole/196.97g) ?
- How do you measure the slope of a line?
divide how much it rose by how far it went; if “downhill” it is negative. In other words, slope = rise/run
- What is the difference between an atom and an ion?Give an example of an atom , an ion,a cation,an anion, a polyatomic anion, a polyatomic cation, and a polyatomic anion.
atoms such as carbon (C) are uncharged. Ions such as Na+ are charged (negative for an anion, positive for a cation). If the ion is one atom only like P it is monatomic. If it has more than one atom like CO32- it is polyatomic.
- What is the difference between an atom and a molecule?
A molecule is two or more atoms bonded together.
- Compare the Fe (II) ion and the Fe (III) ion.
Well, the big difference is that the III ion has lost one more electron. The Fe (II) ion, also known as the ferrous ion, has a charge of +2. The Fe (III) ion, also known as the ferric ion, has a +3 charge. Either can form under the right conditions, this is a good example of a polyvalent ion.
- What is the ratio of anions to cations in chromium(III) oxide?
The formula is Cr2O3, so the ratio is two cations for every three anions. That way the charges total 6 for each.
- Tell me about monovalent metals
They only have one charge. They are mostly groups one and two. A couple from group 3.
32. List some monatomic and polyatomic ions
Monatomic means one atom, Na+, Li+, Cl-, Ca2+, Al3+for example. Polyatomic ions have more than one atom to form an ion, like a carbonate (CO32-) for example.There are lots more at the bottom of the class periodic table.
33. List one polyatomic cation
The only one on our list is NH4+, also known as the ammonium cation
- List the charges of the metallic ions in aluminum oxide, and MnCO3.
aluminum is +3 always, oxide is -2 always, The carbonate is always -2, and manganese is polyvalent but since there is one carbonate it must be +2.
- What is the typical electronic behavior of metals, nonmetals, and noble gases?
Metals lose electrons. Some such as gold do so reluctantly. Non metals gain electrons or and can do so by taking them, or sharing them. And the noble gases don’t do anything at all.
- Which are multivalent: Cr, Fe, Mg, O?
Chromium and iron; they are in the “roman numeral region”
- How many atoms of fluorine are in the molecule carbon tetrafluoride, CF4?
a.1c.4that was pretty easy…
- What is the formula for a compound formed by aluminum and the sulfate ion, SO4-2?
since aluminum forms a +3 cation we get Al2(SO4)3
- What is the formula for the compound formed by Iron(II) ions and chromate ions, CrO4-2?
They offset nicely: FeCrO4
- The formula for dinitrogen heptoxide is N2O7
- The formula for magnesium oxide is MgO
- What is the formula for the compound formed by the barium ion and the phosphate ion?
- Name the compound W3(PO4)2.
that would be tungsten (II)phosphate
44.Name the compound KClO2.
I name thee potassium chlorite.
45. Name the compound Fe2O.
I hereby christen thee Iron (I)oxide
46. The symbol used in a chemical reaction to indicated that some substance is dissolved in water is (aq) for aqueous
47. The symbol used in a chemical reaction to indicate that some material is boiled is (g) for gas
48. Tell me about an opaque solution.
The fact that it is opaque means it is homogeneous, as long as it is uniformly opaque. That's based on the idea that if only one thing is visible for a solution we call it homogeneous. The fact that it is a solution means that it is a mixture…I’d say we got ourselves a heterogeneous mixture.
49. In a reaction, the ions of two compounds exchange places in aqueous solution to form two new compounds. This reaction is called a omit!...though later we will call it a double replacement reaction
50. The solid compound formed in a double-displacement reaction is called a omit!
51.Describe a synthesis reaction, and a decomposition reaction, and a single replacement reaction, and a combustion reaction
omit this too!
52. Balance the following chemical reaction:
4 Al + 3O2à2 Al2O3
53. What is the total number of molecules , and atoms represented by the following equation?
33 molecules, …28 + 26 +24 + 30 = 108 atoms
54. Write a balanced chemical equation for the synthesis of carbon dioxide from the elements.
C + O2à CO2
56.Sulfur can exist as S8. Use it to create a balanced chemical equation for the synthesis of sulfur tetrachloride.
S8 + 16Cl2à 8SCl4
- Why don’t chemists count atoms and molecules directly?
Well they could try, but there are justtoomany
- An Avogadro’s number of any element is equivalent to
a.the atomic number of the element
b.6.022 x 1023 particles
c.the mass number of that element
d.12 g of that element
and it is worth noting that molar mass, as the name implies, would be the mass of those 602 septillion particles.
59. Which substances can not be decomposed by chemical means?
atoms; they can be decomposed but its called a nuclear process
60. Examples of data with high and low precision, accuracy
For precision you need repeatable numbers, like 3, 2.99, 3.01. For accuracy one needs an accurate number to compare it to: If it is 3:00 pm and your watch says 3:01 that’s fairly accurate.
61. Lewis dots are electron dots. Do aluminum, and iodine and the nitrogen trianion.
Aluminum has three spread out, iodine has seven consisting of three lone pairs and a single bonding electron, and N3- has all 8 electrons, in 4 pairs.
62. Electron configuration and orbital notation…what’s the difference? Do a fairly big one like tin.
Tin ends with with 5p2…hope that’s enough for most of you. Here is an even bigger one: seaborgium:
63. Write out the seven units we covered. Come up with a diagram that shows how they relate, at least to you.
you are on your own for this but it is very helpful for organizing your mind.
64. What is everything made out of?Write a paragraph that summarizes you current thinking.
Please do on your own.
5t. The electron test review
5t1 questions 1-3(sharper )5t2 questions 4-6(sharper)
5t3 questions 7-10 (sharper) 5t4 questions 11-12
5t5 questions 13-14(sharper)5t6 questions 15-16(sharper)
5t7 questions17(sharper)5t8 questions 18-19(sharper)
5t10 question 20(sharper) 5t21 question 21 (sharper)