[iceboy99]

I just had my final exam for chemistry and I really messed up this one question. This is the first chemistry class I've ever taken so obviously I'm not an expert on the subject. The equation I had to balance was Barium nitrate  added to Iron(III)  Sulfate. Heres how I wrote it. Ba(NO3)2 + Fe2(SO4)3 ---> BaSO4 + FeNO3 . and for the life of my I couldn't balance it. So I just got home and I input the equation into an online balancer to find the equation should've came out to be   
Ba(NO3)2 + Fe2(SO4)3 ----> BaSO4 + Fe(NO3)3. I got the whole question wrong because I didn't give the Iron a 3+ charge on the products side of the reaction. The rest of the problem involving moles and limiting reactants, which I know how to do. This question was worth nearly 40 points and I got a 0. I'm taking chemistry next semester and I just want to know how I can prevent this from ever happening again. Thanks

[Borek]

To be honest - I have no idea what to tell you. There is no other way of preventing things like that than solving problems so that you get fluent.

There was already Fe(III) on the left hand side of the equation, this is not a redox reaction so there is no way for Fe to change the oxidation state. Iron nitrate written as you did it is wrong at the first sight, there is simply not such compound, NO₃^- has a single negative charge, salt must be neutral, so the XNO₃ needs o single positive charge cation X⁺, iron in salts is typically either Fe²⁺ or Fe³⁺.

[MNIO]

you should think about the possible reactions that might occur
   (1).. A + B ----> AB.. ... ... ... ... ... .. . synthesis
   (2).. AB ----> A + B.. .. ... . .. ... .. .. decomposition
   (3).. AB + C ---> AC + B.. ... ... ... ... .single displacement
   (4).. AB + CD ---> AD + CB.. .. ... .. ..double displacement
   (5).. CxHy + O2 ---> CO2 + H2O.. . ..combustion
   (6).. HX + YOH ---> H2O + YX.. .. . . neutralization

and of course.. REDOX.

without more information other than Ba(NO3)2 + Fe2(SO4)3 --> what? and balance it.. you should start by thinking this.
   (1) it would be very difficult to predict the products of a REDOX reaction without more info
   (2) simple is usually better
   (3) precipitates will drive the reaction forward.

and then try one of those reaction types... like #4 in this case.. double replacement
  __ Ba(NO3)2 + __ Fe2(SO4)3 ----> __ BaSO4(s) + __ Fe(NO3)3

and barium sulfate is insoluble in water.  The rest is simple

[Fish200398]

how we known inorganic compound soluble in water or not?

[AWK]

Someone checked it once and it created a set of several rules that are worth remembering.
https://scienceprojectideasforkids.com/general-solubility-rules/
There are sometimes exceptions to the rules!

https://wiki2.org/en/Solubility_table

[hypervalent_iodine]

This is a little off topic, but I find it unfortunate you didn't get marked correct on the subsequent limiting reagent etc. questions (assuming you got them right based on your faulty first answer). Where I am, we make a point of not double penalising students for wrong answers. If, like you, they got the first answer of a series of questions wrong, but every subsequent answer was correct based on the first wrong answer, then they would get full marks for those answers and only lose marks for the first one. After all, we are trying to assess your understanding of the content. If you have correctly applied the course content and demonstrated you understand what you're doing, there's no reason you should be marked down (IMO).

As to your issue, there are just some things you have to know how to do and the only way is to practice and practice and then practice some more until you can answer the questions in your sleep.