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# Hard chemistry question AS

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1. The equation for the hydrogenation of ethyne is C2H2 + 2H2 --> C2H6.
The experimental yield is 65%.
What is the mass I'm grads of ethane that can be produced from 16.20g of hydrogen.

2. hi
Experimental yield =(theoretical number of moles)/(actual number of moles) * 100...equation 1

from the equation n(H2) : n(C2H6)
2;1

n(H2) = 16.2/2
=8.1 moles

n(C2H6) = 1/2 * n(H2
= 1/2 * 8.1
= 4.05 moles

let the theoretical number of moles be x

from equation one
Experimental yield = 65
actual number of moles of C2H6 = 4.05 moles
theoretical number of moles of C2H6= x moles

therefore 65 = x/4.05 *100
65/100 = x/4.05
0.65 * 4.05 = x
2.6325 moles = x

mass (C2H6) = Mr(C2H6) * n(C2H6)
= 30 * 2.6325
=78.975 g
oops ours answers are slightly different but give it a check in the working

anywhere check this one out

Calculating Experimental Yields
1. Ensure you have a correctly balanced equation for the reaction performed.
2. Determine how many moles of each species were used in the reaction.
3. Determine which species is the limiting reagent, remembering to use the reaction stoichiometry.
4. From the weight of product obtained, determine how many moles of product this corresponds to.
5. Taking into account the stoichiometry, determine what % this is compared to what you could have obtained by 100 * [moles product obtained]/[ maximum moles product possible]

For example: 8.21g of cyclohexene was reacted with 17.5g of bromine in chloroform, giving 20g of trans-1,2-dibromocyclohexane.

Stoichiometry of this reaction is 1:1
Moles of each species involved:
cyclohexene = 0.10 mol, Br2= 0.11 mol, dibromocyclohexane = 0.083 mol.
Limiting reagent is therefore the cyclohexene.
Theoretical yield of dibromocyclohexane is 0.10 mol., therefore, experimental yield = 0.083./0.10 = 83 %

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