chemistry final exam
CocoA886
chemistry2bfinal2bexam2bv2d.docxChemistry Final Exam Version 4/7/15
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Directions: It is important that you provide answers in your own words. Please focus only on information from the text/eBook to create your own solutions. Please do not use direct information from an outside source (especially copying and pasting from an “answer” website). Use of direct information from an outside source is against school policy. All answers will be checked for plagiarism. Instances of plagiarism can result in probation or possible dismissal from the school.
Please be sure to follow all guidelines (number of sentences/showing all calculations) and to provide the correct metric units of measure. All questions are 5 points (1 point for sentence number /units).
1. A student collected the following data for a fixed volume of gas:
|
Temperature (⁰C) |
Pressure (mm of Hg) |
|
10 |
726 |
|
750 |
|
|
40 |
800 |
|
70 |
880 |
|
100 |
960 |
|
150 |
??? |
Fill in the missing data point. Show all calculations leading to an answer.
From the chart, we can find if the temperature raised the fixed volume of gas increased.
Set the pressure (mm of Hg) as “Y” the temperature (℃) as X; we may have the binary quadratic equations as Y = aX2 +bX +c;
Use the related data in the form, we may have the formula as:
· 726=100a+10b+c
· 750=400a+20b+c
· 800=1600a+40b+c
2. You are given a clear solution of KNO3. Using 3 – 4 sentences (in your own words) explain how you would determine if the solution is unsaturated, saturated or supersaturated.
· Continue to increase KNO3, if it dissolve, unsaturated. If insoluble, saturated or supersaturated
· Supersaturated is not a stable state, shake it vessel or change a little environment, if you find white solid, it is supersaturated. If not, saturated.
3. Explain why gasoline will not dissolve in water.
According to the principle of "similarity", "similar" means that the solute and solvent are similar in structure or polarity, so the type and size of the molecule is similar. The molecular weight of gasoline is greater than that of water，so it cannot dissolve in water.
4. Explain in 3 – 4 sentences (in your own words) how perspiration helps keep you cool on a hot day.
Perspiration throughout from the skin and take away part of the body heat makes you cool on a hot day.
5. You have two sealed jars of water at the same temperature. In the first jar there is a large amount of water. In the second jar there is a small amount of water. Using 3 -4 sentences explain how the vapor pressure of water in the first jar compares with the vapor pressure of water in the second jar.
M = 1 kg, t = 100 degrees Celsius, t = t + 273 = 373 Kelvin, v = 1 cubic meter, gas universal constant R = 8.28 joules / (Kelvin * mol)
Because the molar mass of water is 18 grams, so the mole number of 1 kg of water vapor is n = 1000 / 18 = 500 / 9 mol
By claperon equation
PV = nRT
P = nRT = V = (n/ 18) *8.28*373 / 1 = 171.58nPa
So,Set the weight of the water in the first jar as n1 the weight of the water in the second jar as n2,
We may know that the vapor pressure of the water in the first jar compares with the vapor pressure of water in the second jar is just n1/n2; Only the weight ratio.
Only need to weighted and calculate the pressure.
6. Using 3 – 4 sentences explain (in your own words) why water expands when it freezes?
H2O(s)→H2O(l) is an endothermic process, The density of water in the solid state is lower than that in the liquid form.
Because Density↑ = mass（unchanged） * Volume↑
Expand.
7. Using your knowledge of colligative properties explain whether sodium chloride or calcium chloride would be a more effective substance to melt the ice on a slick sidewalk. Use 3 – 4 sentences in your explanation.
Sodium chloride, calcium chloride to chloride snow-melting agent, they dissolve in water (snow), containing salt snow freezing point below 0°, the road area of snow to ice, such as calcium chloride dissolved in water after coagulation in minus 20 ° for about
8. When a 2.5 mol of sugar (C12H22O11) are added to a certain amount of water the boiling point is raised by 1 Celsius degree. If 2.5 mol of aluminum nitrate is added to the same amount of water, by how much will the boiling point be changed? Show all calculations leading to your answer OR use 3 – 4 sentences to explain your answer.
b(C12H22O11)=2.5mol/m(water)
b(Al(NO3)39H2O)=2.5mol/m(water) the answer is 1°
If you add 2.5g sugar and the same weight of aluminum nitrate , the answer is not easy.
Ar(C12H22O11)=342.3 Ar(Al(NO3)39H2O)=375.13 Ar(Al(NO3)39H2O)/Ar(C12H22O11)=1.09
b(C12H22O11)=2.5g/342.3/m(water)
b(Al(NO3)39H2O)=2.5g/375.13/m(water)
9. If 5.40 kcal of heat is added to 1.00 kg of water at 100⁰C, how much steam at 100⁰C is produced? Show all calculations leading to an answer.
1KG 100° water need 539Cal to produce 1KG steam.
1Cal=1000cal 539Cal=539000cal
So the answer is 5400cal/539000cal*1kg=0.01kg steam
10. The freezing of water at 0⁰C can be represented as follows:
H2O (l) ↔ H2O(s)
The density of liquid water is 1.00 g/cm3. The density of ice is 0.92 g/cm3. In 3 – 4 sentences explain why applying pressure causes ice to melt.
P = nRT
P ↑= n（unchanged)R(unchanged)T↑
So applying pressure causes ice to melt because applying pressure equals increase temperature
11. The Kw of water varies with temperature. Calculate the pH of water at 46⁰C with a Kw = 1.219 x 10-14. Show all calculations leading to an answer.
PH=-lg[H+]=-lg[1.1041 x 10-7] =6.96
12 Calculate the hydroxide ion concentration of a solution with pH = 3.25. Show all calculations
PH=3.25 POH=10.75 c(OH-)=1.0*10-10.75 c(H+)=1.0*10-3.25 kw=5.62*10-4
13. What salt results from the neutralization of phosphoric acid with potassium hydroxide?
H3PO4 + KOH = KH2PO4 + H2O KH2PO4 + KOH = K2HPO4 + H2O K2HPO4 + KOH = K3PO4 + H2O
account the acidity and alkalinity, you will have three salt.
12. What is the oxidation number of chlorine in Al(ClO4)3?
AL(OH)3+3HCLO4=3H2O+AL(CLO4)3
The answer is 0
13. Which element is oxidized in the following reaction:
CuO(s) + H2 (g) Cu(s) + H2O (l)
H2 CuO(s)→Cu(s) out of O H2(g)→H2O（l) get O and change shape
14. Why must the number of electrons lost equal the number of electrons gained in every redox reaction? Use 3 – 4 sentences in your own words to address this question.
In the process of chemical reaction, the type of atom before and after the reaction has not changed, the number of atoms has not increased or decreased, and the quality of the atom has not changed, so the total quantity of the material before and after the chemical reaction must be equal.
Chemical change in the "certain": the atomic species, the number of atoms, atomic weight, element type, the quality of the elements and the total mass of the material before and after the reaction must be constant;
The "change" in the chemical change; the molecular species and the species of the material must be changed;
The chemical changes in the "change": the number of molecules may change, valence
15. The following unbalanced equation describes the reaction that can occur when lead (II) sulfide reacts with oxygen gas to produce lead (II) oxide and sulfur dioxide gas:
PbS + O2 PbO + SO2
Balance the equation and describe in words the electron transfer(s) that takes place.
+2-2 0 +2-2 +4-2 -2 +4
PbS + O2 → PbO + SO2 S →S get 6 electron and O lose 2electron per atom
16. What type of radiation is emitted when chromium-51 decays into manganese-51? Show the nuclear equation that leads you to this answer.
17. A radioactive nucleus alpha decays to yield a sodium-24 nucleus in 14.8 hours. What was the identity of the original nucleus? Show the nuclear equation that leads you to this answer.
10n+2713AL→2411Na+42He α nucleus
18. Iron-59 has a half-life of 45.1 days. How old is an iron nail if the Fe-59 content is 25% that of a new sample of iron? Show all calculations leading to a solution.
Half-life of 45.1 days 100%-50%-25% 2cycles 45.1*2=90.2days.
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