Mr Study's 3/4 Questions

[BoredSatan]

the dot doesnt really mean anything.. but i think it means that when this compound is heated, the h20 would be lost.. so it would depend if the question is asking for the mole of hydrated iron nitrate or just iron nitrate

[Mr. Study]

Ahh! I get what your saying. Thanks.

[Mr. Study]

Quick question regardng balancing equations.

Is it alright if we use a fraction (1.5, 2.5...) to balance an equation out? Or do we have to use only whole numbers?

Thank you.

[Phy124]

Quick question regardng balancing equations.

Is it alright if we use a fraction (1.5, 2.5...) to balance an equation out? Or do we have to use only whole numbers?

Thank you.

Occasionally I see people use fractions, but I think it's better to use whole numbers. I believe it can also decrease the chances of making a mistake when doing the ratios in conversion.

[Shenz0r]

Use whole numbers, definitely. Fractions in balanced equations are a big no no. Multiply everything by a certain number to ensure that you don't get left with fractions in your balanced equation.

[Mr. Study]

Regarding sig figs, would we consider the sig figs of temperature, if it were given in the question?

Example: Find the number of moles of 500.4 ml, 101.3 kPa, 20 degrees.

mole = pV/RT = 101.3 X 0.5004/8.31 X 20 = 0.30499 = 0.3049 mol or would it be 0.30 as the 20 degrees is the least accurate amount, given in the question?

Thank you.

[watto_22]

Regarding sig figs, would we consider the sig figs of temperature, if it were given in the question?

Example: Find the number of moles of 500.4 ml, 101.3 kPa, 20 degrees.

mole = pV/RT = 101.3 X 0.5004/8.31 X 20 = 0.30499 = 0.3049 mol or would it be 0.30 as the 20 degrees is the least accurate amount, given in the question?
Thank you.

You would have to say 0.30 since the 20 degrees is only two sig figures

[Somye]

is the degrees kelvin or Celsius? because if it was celsius, your value would be 293 and hence your significant figures would be 3..... but you would also ave to adjust your calculations accordingly

[Shenz0r]

If you use the equation PV = nRT you MUST, MUST use kelvins because the constant R is 8.31 joules per mol per kelvin.

[Mr. Study]

^ Thanks for that. I forgot to change to kelvins damn it!! 

Just a quick question. Is there any quicker way of identifying how many isomers are possible with an alkene?

Such as C₅H₁₀?

[Somye]

If it's just an alkene without functional groups, a simple way is to simply halve the amount of carbons, which in this case leaves you with 2.5. Then round down to the nearest whole number to give you 2!

For example hexene has 3 structural isomers...

[Shenz0r]

If it's just an alkene without functional groups, a simple way is to simply halve the amount of carbons, which in this case leaves you with 2.5. Then round down to the nearest whole number to give you 2!

Pentane actually has three isomers: your normal pentane, 2-metylbutane and 2,2-dimethylpropane.

[pi]

If it's just an alkene without functional groups, a simple way is to simply halve the amount of carbons, which in this case leaves you with 2.5. Then round down to the nearest whole number to give you 2!

Pentane actually has three isomers: your normal pentane, 2-metylbutane and 2,2-dimethylpropane.

He's referring to Alkenes, his method works for alkenes

[Shenz0r]

My bad, it's easy to mistake the -ene for an -ane

[Phy124]

My bad, it's easy to mistake the -ene for an -ane

Just don't mistake them in an Exam!