Answer: The correct answer is (D).
Explanation:
Space photography help astronomers:
- To visualize and observe the position and appearance of celestial objects like: path of orbiting planets ,dim stars which invisible to naked eyes ,far away galaxies etc.
- To observe any phenomena which is occurring at macro level for example: collision of steroids and meteors etc.
Answer:
7.82 g of Cu
Explanation:
2 moles of Al react to 3 moles of copper sulfate in order to produce 3 moles of copper and 1 mol of aluminum sulfate.
Firstly we determine the moles of reactant.
As copper sulfate is in excess, Al is the limiting.
2.75 g . 1mol /26.98g = 0.102 moles
Ratio is 2:3. 2 moles of Al, can produce 3 moles of Cu
So the 0.102 moles of Al will produce(0.102 . 3) /2 = 0.153 moles.
We convert moles to mass: 0.153 mol . 63.5g /mol = 9.71 g
That's the theoretical yield (100 % yield reaction)
We know that: (yield produced / theoretical yield) . 100 = percent yield
We replace:
(Yield produced / 9.71g) . 100 = 80.5 %
(Yield produced / 9.71g) = 0.805
Yield produced = 0.805 . 9.71g = 7.82 g
You can do this by dividing by the molar mass of Zn:
Explanation:
For all of the questions, do the following calculation

As an example, I'll do question 1

Explanation:
It is known that rate of effusion of gases are inversely proportional to the square root of their molar masses.
And, half of the helium (1.5 L) effused in 24 hour. So, the rate of effusion of He gas is calculated as follows.
= 0.0625 L/hr
As, molar mass of He is 4 g/mol and molar mass of
is 32 g/ mol.
Now,

= 2.83
or, rate of
= 
Rate of
= 0.022 L/hr.
This means that 0.022 L of
gas effuses in 1 hr
So, time taken for the effusion of 1.5 L of
gas is calculated as follows.
= 68.18 hour
Thus, we can conclude that 68.18 hours will it take for half of the oxygen to effuse through the membrane.