Stoichiometry HELP!

Cyclohexane (C6H14) can be manufactured from hexane (C6H12) and hydrogen gas. Calculate the mass of cyclohexane that can be made from 258g of hexane.

Firstly, you have the chemical formulas mixed up. Hexane is a 6 carbon chain alkane and the general formula of an alkane is CnH2n+2, so the formula for hexane is C6H14. Cyclic alkanes have 2 less hydrogen atoms than a chain alkane so the formula of cyclohexane is C6H12.

Firstly you need to write a balanced symbol equation for the reaction:
C6H12 + H2 ----> C6H14

Then calculate the number of moles of hexane using mass/Mr:
258g/86.0 = 3 moles

From the balanced equation we can see there is a 1:1 ratio between hexane and cyclohexane in this reaction. This means 3 moles of cyclohexane can be made from 258g of hexane.

Now you need to calculate the mass of cyclohexane, which can be done by multiplying the Mr by the number of moles:
3 x 84.0 = 232g

232g of cyclohexane can be produced from 258g of hexane.