[Lachln]

Also, if you would feel like helping me again, I'm confused about the logic behind the following question:

"Nitric oxide reacts with oxygen to form nitrogen dioxide. 75mL nitric oxide and 50mL oxygen, both at 101.3kPa and 19°C, were mixed. What will the final volume (at the same temperature and pressure) after complete reaction? Calculate the partial pressures in the final gas mixture. Calculate the mass of nitrogen dioxide formed."

So the balanced equation is 2NO + O₂ --> 2NO₂
75×2/2=75mL
50×2/1=100mL
75+100=175mL
175/2=87.5mL

Is that the correct thinking? The answers I have agree with those calculations.

I don't get the second part. The answers say O₂=14.5kPa and NO₂=86.8kPa and the mass of NO₂produced is 0.144g; however, I don't really trust the answers.

[mjc123]

So the balanced equation is 2NO + O2 --> 2NO2
75×2/2=75mL
50×2/1=100mL
75+100=175mL
175/2=87.5mL

Is that the correct thinking? The answers I have agree with those calculations

The answer happens to be right; I have no idea what your thinking was. Why do you multiply 50 by 2 and add to 75?
75 mL of NO (the limiting reagent) react with 37.5 mL O₂ to give 75 mL NO₂, with 12.5 mL O₂ unreacted. Total vol = 75 + 12.5 = 87.5 mL.

I don't get the second part. The answers say O2=14.5kPa and NO2=86.8kPa and the mass of NO2produced is 0.144g; however, I don't really trust the answers.

Why don't you trust the answers? They're right. What intuition suggests to you they might be wrong?
There is a way of talking about gas mixtures that can be confusing; talking as if each gas occupied a certain volume at the total pressure. That happens to be the easiest way of answering the first question, but of course it isn't really like that. The gases are mixed, and each occupies the whole volume, with a partial pressure proportional to its mole fraction. So rather than saying we have 12.5 mL of oxygen at 101.3 kPa, we actually have 87.5 mL of oxygen at a partial pressure of 101.3 * 12.5/87.5 = 14.5 kPa.

[Borek]

Why don't you trust the answers?

Please remember it all started with a problem that was worded in such way it was impossible to solve (here). I am not surprised OP doesn't trust questions not answers now.