School and Work

What is the total pressure in mmHg of a gas mixture containing argon gas at 0.40 atm, helium gas at 395 mmHg, and nitrogen gas at 340 torr??

Question 2:
A gas mixture contains oxygen and argon at partial pressures of 0.60 atm and 375 mmHg....If nitrogen gas added to the sample increases the total pressure to 1280 torr, what is the partial pressure in torr of the nitrogen added?

Question 3:
Aluminum oxide can be formed from its elements. 4Al(s)+3O2(g)--->2Al2O3(s)
Part A
What volume of oxygen is needed at STP to completely react 5.0 g of aluminum?

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A 0.11 gram sample of pure barium was added to 100cm^3 of water.

Ba + H20 ---> Ba(OH)2 + H2

Calculate the concentration, in moldm^-3, of the Ba(OH)2 solution formed.

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I am clueless. Please show working, I don't even know where to begin.

The answer is 8 x10^-3 by the way. (In given answers)

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