Questions

[Hye]

Hey. need help on these questions.

1.A commercial pest stripe uses a pesticide called dimethyl dichlowovinyl phosphate (DDVP) that has a molar mass of 221. Each pest strip weighs 29.0g and contains 18.6% by mass of DDVP
What mass of pest strip would have to be swallowed by a 10kg dog to receive a lethal amount? (Lethal amount for a dog is 30mg of DDVP per kg of dog weight)

2.When 50mL of 0.2M HCl and 50mL of 0.2M Ba(OH)2 are mixed, what will the pH of the resulting solution be?

3.
2NaHCO3 -> Na2CO3 + CO2 +H2O
One cake requires 4.0g of NaHCO3. The cake is to be baked in an oven at 200 C. What is the volume in litresof the CO2 that would be released? Assume pressure is 104kPa

I got 0.90 as the volume, can someone confirm this.

The indicator chosen forthis titration is methyl orange, which changes colour from yellow to pink when all of the carbonate ions havebeen converted to carbon dioxide. This will occur when the number of
A.   H+ ions just exceeds the number of CO32- ions present originally
B.   H+ ions added just equals the number of CO32- ions present originally

Which one do you guys think?

[simonhu81292]

1.
so lethal amount for the 10KG dog would be 30mg X 10 = 300mg..
300mg equals 0.3g... ..
therefore 18.6%of x ... x is the mass of pest strip .  18.6% of x =0.3g
0.3 divide ( 18.6/100) gives you the answer... 1.61g  


yeah Q3.. the answer is 0.9L

[physics]

EWWWW pH that stuff is AOS2 i think...in AOS1 they mentioned something about the pH but it was like a small paragraph and i totally forgot it all :"(

[simonhu81292]

i think it would be A for you question 4 ...
i did try question 2 ... i am not 100% sure ...
but it might be pH of 7..
do you have the answer to that ques?

[Hye]

Why would you say it's A?

Apparently the answer is 13.0

mmm

[vexx]

2.When 50mL of 0.2M HCl and 50mL of 0.2M Ba(OH)2 are mixed, what will the pH of the resulting solution be?

calculate moles of both
0.01 mol of HCL and 0.01 mol of Ba(OH)2
2:1 ratio
so 0.01 mol of HCl reacts with 0.005 mol of Ba(OH)2
this means only half of the Ba(OH)2 was neutralised, so there is 0.005mol left over in excess, and this excess determines the pH of the solution
c(Ba(OH)2)=0.005mol/0.050L
= 0.1
then -log(.1)=1
and since we are looking for the concentration of (OH-) we do 14-1 = 13.0 pH

[simonhu81292]

okay for ques 2 ...i think you find the
pH of the 2 separately and then combine them
so pH of the HCl is around 0.7
and the pH of the Ba(OH)2 is around 13.6
thuse by adding them together
13.6 - 0.7 = 12.9
which is around 13
and yeah ..is A right?
because when they say equal.. i think of the equivalence point
and exceed the end point .. that's when the colours change ..

[vexx]

okay for ques 2 ...i think you find the
pH of the 2 separately and then combine them
so pH of the HCl is around 0.7
and the pH of the Ba(OH)2 is around 13.6
thuse by adding them together
13.6 - 0.7 = 12.9
which is around 13
and yeah ..is A right?
because when they say equal.. i think of the equivalence point
and exceed the end point .. that's when the colours change ..

haha too late soz i already answered:(

[Hye]

Thanks

This is a similar question
if 150mL of 0.10M NaOH is mixed with 50mL of 0.30M HCl, then the pH of the resultant solution is closest to?

A.7 B.1 C.13 D.2

it's one to one, how would we go about this?

Ty

[vexx]

Thanks

This is a similar question
if 150mL of 0.10M NaOH is mixed with 50mL of 0.30M HCl, then the pH of the resultant solution is closest to?

A.7 B.1 C.13 D.2

it's one to one, how would we go about this?

Ty

it's the same hye:)
just find the amount in excess and then use that to determine the concentration of that substance.

so 0.015mol NaOH + 0.015mol HCl
1:1 ratio, all reacted in same proportions.

Therefore pH=7

Pretty sure that's right:)