- #1
TripleS
- 22
- 0
Question 1:
In the early years of the nineteenth century, John published a list of atomic masses. One experiment on which it was based involved measuring the composition by mass of ammonia. By assigning hydrogen a mass of 1 unit and using the chemical formula for ammonia, he could deduce the atomic mass of nitrogen.
Unfortunately, he incorrectly believed that the formula for ammonia was NH. What atomic
mass did he propose for nitrogen on the basis of this formula?
None?
Molar Mass of NH3 = 17
Thinking H is 1, and the formula is NH then
N = 16? (Except this is wrong...)
Question 2
A brown-black compound of thallium was found to contain 89.5% Tl and 10.5% O. What is
the oxidation number of thallium in this compound?
None again?
204.4 / 89.5 = 2.28
16 / 10.5 = 1.52
2.28 x 2 = 4.5 ish
1.52 x 3 = 4.5 ish
so 3 oxygens to 2 thalliums...so 3+
but I am pretty sure that's not how you do it...its the right answer though...
Question 3
A sample of phosphorus pentachloride is placed in a sealed container, where it decomposes into phosphorus trichloride and chlorine gas.
Once the mixture is at equilibrium, a small quantity of helium gas is added, at constant pressure and temperature, and the mixture is allowed to return to equilibrium. Which of the following best describes the second equilibrium position with respect to the first?
A - The second equilibrium position is the same as the first, because helium is much
lighter than any of the other molecules in the container and will have a negligible
effect on the reaction.
B - The second equilibrium position is the same as the first, because helium does not
react with any of the other molecules in the container.
C - The second equilibrium position has more PCl3 than the first.
D - The second equilibrium position has more PCl5 than the first.
E - It is impossible to tell what will happen without knowing the equilibrium constant
for this reaction.
PCl5 (g) <---> PCl3 (g) + Cl2 (g)
Addition of helium would increase the number of gas particles and the system would then react to the left in order to decrease the increased pressure.
So I would choose D, except the answer was C
Question 4:
Q14 An unknown compound was discovered to have molecular formula C10H20O2. To which of the following classes of compounds could this unknown not belong?
A - alkynes
B - alkenes
C - alcohols
D - esters
E - ethers
Alkynes = CnH2n-2
Alkenes = CnH2n
It could be a decene-diol, so A and C would work.
And i wasn't sure about the rest (I wasn't sure what a ester or ether was ><)
Homework Statement
In the early years of the nineteenth century, John published a list of atomic masses. One experiment on which it was based involved measuring the composition by mass of ammonia. By assigning hydrogen a mass of 1 unit and using the chemical formula for ammonia, he could deduce the atomic mass of nitrogen.
Unfortunately, he incorrectly believed that the formula for ammonia was NH. What atomic
mass did he propose for nitrogen on the basis of this formula?
Homework Equations
None?
The Attempt at a Solution
Molar Mass of NH3 = 17
Thinking H is 1, and the formula is NH then
N = 16? (Except this is wrong...)
Question 2
Homework Statement
A brown-black compound of thallium was found to contain 89.5% Tl and 10.5% O. What is
the oxidation number of thallium in this compound?
Homework Equations
None again?
The Attempt at a Solution
204.4 / 89.5 = 2.28
16 / 10.5 = 1.52
2.28 x 2 = 4.5 ish
1.52 x 3 = 4.5 ish
so 3 oxygens to 2 thalliums...so 3+
but I am pretty sure that's not how you do it...its the right answer though...
Question 3
Homework Statement
A sample of phosphorus pentachloride is placed in a sealed container, where it decomposes into phosphorus trichloride and chlorine gas.
Once the mixture is at equilibrium, a small quantity of helium gas is added, at constant pressure and temperature, and the mixture is allowed to return to equilibrium. Which of the following best describes the second equilibrium position with respect to the first?
A - The second equilibrium position is the same as the first, because helium is much
lighter than any of the other molecules in the container and will have a negligible
effect on the reaction.
B - The second equilibrium position is the same as the first, because helium does not
react with any of the other molecules in the container.
C - The second equilibrium position has more PCl3 than the first.
D - The second equilibrium position has more PCl5 than the first.
E - It is impossible to tell what will happen without knowing the equilibrium constant
for this reaction.
Homework Equations
PCl5 (g) <---> PCl3 (g) + Cl2 (g)
The Attempt at a Solution
Addition of helium would increase the number of gas particles and the system would then react to the left in order to decrease the increased pressure.
So I would choose D, except the answer was C
Question 4:
Homework Statement
Q14 An unknown compound was discovered to have molecular formula C10H20O2. To which of the following classes of compounds could this unknown not belong?
A - alkynes
B - alkenes
C - alcohols
D - esters
E - ethers
Homework Equations
Alkynes = CnH2n-2
Alkenes = CnH2n
The Attempt at a Solution
It could be a decene-diol, so A and C would work.
And i wasn't sure about the rest (I wasn't sure what a ester or ether was ><)