Calculate the concentration of buffer components present in 295.00 mL of a buffer solution that contains 0.390 M NH4Cl and 0.390 M NH3 immediately after the addition of 1.40 mL of 6.00 M HNO3.

Explanation:

The acid HNO₃ will react with the base NH₃ in the buffer to produce NH₄⁺, changing the concentrations of both NH₃ and NH₄⁺ in the buffer.

Therefore, this question is solved by performing stoichiometric calculations based on those reactions:

HNO₃       +      NH₃     ⇒        NH₄⁺

Vol HNO₃ = 1.40 mL x 1L / 1000 mL = 1.4 x 10⁻³ L

# mol HNO₃ = 1.4 x 10⁻³ L x 6.00 mol/L =  8.4 x 10⁻³ mol HNO₃

Since the reaction occurs in 1:1 ratio, 8.4 x 10⁻³ mol NH₃ will be consumed and 8.4 x 10⁻³ mol of NH₄⁺ will be produced.

Initially we had

# mol NH₄⁺ = 0.295 L x 0.390 mol/L =  0.115 mol

# mol NH₃ = 0.115

After reaction we will have

# mol NH₄⁺  = 0.115 mol + 8.4 x 10⁻³ mol = 0.123 mol

# mol NH₃ = 0.115 mol - 8.4 x 10⁻³ mol = 0.107 mol

Therefore, their new concentrations will be

Volume after reaction = 0.295 L +0 .0014 L = 0.296 L

[NH₄⁺] = 0.123 mol / 0.296 L = 0.416 M

[NH₃] = 0.107 mol / 0.296 L = 0.361 M

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.

може ли да зареждате повече информация, моля