Question

a sample of ethanol was prepared by reacting 9.2cubic centimetres of ethanol(density 0.8grams/cubic centimetre)with an acidified solution containing 11grams of sodium dichromate(Na2 Cr2 O7)
the reaction is represented by the following equation:
C2 H5 OH+K2 Cr2 O7+H2SO4=CH3 CHO+Cr2(SO4)3+H2O +K2SO4

1. Balance the equation
2.determine the limiting reagent
3.calculate the percentage yield

Answer 1

Surely you didn't mean that ethanol was used to prepare ethanol. I suspect you meant ethanol was used to prepre ethanAl (acetaldehyde).
3C2H5OH + K2Cr2O7 + 4H2SO4 => 3CH3CHO + Cr2(SO4)3 + 7H2O + K2SO4

You should be able to guess correctly that ethanol is the limiting reagent (LR). Calculate it to confirm.

grams ethanol = volume x density. You know volume and you know density from the problem.
Convert grams ethanol to mols. mol = g/molar mass = ?

Using the coefficients in the balanced equation, convert mols ethanol to mols ethanal. I see a 1:1 to mols ethanol will be the same as mols ethanal.

Convert mols ethanal to grams (if that's what you want) by g = mols x molar mass and that gives you the grams for 100% yield

You can't calculate percent yield because you don't list the mass of ethanal prepared.

Post your work if you get stuck.