07/27/18

Calculate ΔH for the overall reaction in units of joules
A styrofoam cup calorimeter is used to determine ΔH for the acid-base reaction: CH3COOH (aq) + NaOH (aq) ⇔ NaCH3COO (aq) + H2O (l)   when 25.00mL of 0.500M NaOH at 23.00°C is added to 25.00mL of... more
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07/16/18

Effective buffer range?
The Ka for a hypothetical weak acid HX is 3.1 x 10-5. Buffer solutions containing HX and NaX could be prepared to make a range of pH values. What would be the lower and upper pH values of the... more
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07/09/18

How to determine the temperature range at which carbon can reduce iron (III) oxide to iron?
3 Fe2O3 (s) + 3 C (s) --> 4 Fe (s) + 3 CO2 (g)   Is there a certain equation that is used to determine the temperature range? I have calculated the ΔHrxnº, ΔSrxnº, ΔGrxnº I'm not sure if... more
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07/09/18

Heat capacity of the coffee cup calorimeter?
A reaction known to release 1.78kJ of heat took place in a coffee cup calorimeter containing 0.100L of solution where the temp rose by 3.65 deg. C.   In a second experiment, when 50.0mL of 0.20M... more
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06/28/18

Aspirin Synthesis Lab - What chemicals are present in each step?
Aspirin is prepared from salicylic acid via an esterification reaction, which involves forming an ester (ASA) from an alcohol (salicylic acid) and carboxylic acid derivative (acetic anhydride), in... more
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06/21/18

Why is the pH of the first equivalence point, of a titration of polyprotic acid, not equal to7?
A titration of phosphoric acid with sodium hydroxide. The first equivalence point has a pH of about 5.    My thoughts are that because it is only the first equivalence point, only one H+ has been... more
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06/20/18

Calculate the Ka of a weak acid?
A sample of a certain monoprotic weak acid was dissolved in water and titrated with 16.00mL of 0.125M NaOH to reach the equivalence point. During the titration, the pH after adding 2.00mL of NaOH... more
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06/19/18

Calculate pH
[NH4Br](aq) = 0.020M , pKa of NH4+= 9.24   Given that the question is asking for pH, I know I need to find the [H3O+], so I've set up the reaction to look like this: NH4Br (aq) + H2O ⇌ H3O+ +... more
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06/13/18

Using mole ratio to determine concentration of a reactant?
S2O82- + 2 I- --> 2 SO42- + I2   (reaction 1)       [I-]=0.20M, [S2O82-]=0.10M      2 S2O32- + I2 --> S4O62- + 2 I-  (reaction 2)      [S2O32-]= 0.0050M   I need to determine the... more
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06/07/18

What is the concentration of each gas once equilibrium is reached?
Can someone please let me know if I did this right?    1.800 mole of N2O4(g) is injected into a closed 1.00L container. Kc=4.66 x 10-3 at 298K   N2O4 (g) ⇌ 2NO2 (g)   what is the... more
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05/30/18

Is the reaction rate dependent on the concentration of the excess reagent?
If a higher concentration means a higher rate of reaction because of more collisions, then does the reaction rate depend on the concentration of the excess reagent? 
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05/25/18

Calculate the total gas pressure after one half-life?
Decomposition of N2O to N2 and O2 is a first order reaction. At 730 deg. C the half life of the reaction is 3.58 x 103 min. If the initial pressure of N2O is 2.10 atm at 730 deg. C,    a.... more
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05/25/18

How long will it take the reaction to go to 95% completion?
rate constant of second order reaction is 0.80 M^-1 s^-1 Given an initial concentration of 0.086M, how long will it take for the reaction to go to 95% completion?  
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03/20/18

Mass of Aspirin in a tablet
In a lab determining the mass of acetylsalicylic acid in an aspirin tablet, I'm having trouble with the dilution part of my calculation.   An unknown solution was made by placing an aspirin... more
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03/15/18

Do both flasks contain the same number of atoms?
If two identical sealed flasks, one containing He and one containing Ne, are at the same temperature (298 K) but the pressure of He is 1atm and the pressure of Ne is 0.5 atm, will both flasks... more
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03/14/18

Use this information to calculate the molecule formula for the compound
Nicotine is composed of carbon, hydrogen and nitrogen and its molar mass is about 160g/mol. When 4.38mg of the compound burns completely in oxygen, the reaction produces 11.9mg of gaseous... more
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03/06/18

Do moles change with volume?
Does increasing or decreasing volume change the moles in a solution, or does that just affect the concentration?   If I have 0.035711 moles in 100mL and I'm asked how many moles in 5mL of this... more
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03/05/18

Electron Configuration of Cr0
What does the superscript 0 mean?   The question asks for the electron configuration of Cr0 I know if its plus or minus you subtract or add electrons based on that number but what do you do when... more
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03/05/18

How do I use the ideal gas relationship to determine the experimental volume of CO2 at STP?
Average volume of CO2 in the experiment was 37.68mL. water temp 20.08 C vapour pressure of water 17.7 mmHg Barometric pressure 758.3mmHg   P1V1/T1  = P2V2/T2   I know I have to rearrange the... more
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03/01/18

Relative error to absolute error?
I'm asked to use the relative error to find the absolute error of [Na2S2O3]I've calculated these amounts in previous questions:[Na2S2O3] = 0.01001MRelative error: 0.3%is there other information I... more
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02/28/18

C-C bond length in 1, 3-butadiene?
Why is the bond length between the two central carbon atoms 146 pm instead of 154 pm?
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02/23/18

Arrange in the order of increasing percent ionic character
Did I do this correctly?   in increasing order of percent ionic character: N-N, S-O, Cl-F, K-O, Li-F
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02/12/18

Explain on the basis of electronic configuration:
The electron affinity of S is +200kJxmol-1 and of Cl is +348kJxmol-1    
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02/09/18

If l=0, the only possible value for ml would also be 0, right?
I have a question asking the number of electrons in an atom with the following quantum numbers:   n=2  l=0 ml=+1 ms= -1/2   since l=0 the only possible value for ml would also be 0, wouldn't... more
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02/07/18

Orbital Designation?
n=7 l=5 ml=-4 ms=-1/2
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