Question #121594

a mixture of 75 cm3of oxygen and 12.5 cm3 of a gaseous hydrocarbon h were exploded in an eudiometer. after cooling to room temperature, 50 cm3 of gas was left and when this was shaken with koh solution, 12.5 cm3 of oxygen remained. given that all the volumes were measured at same temperature and pressure, calculate the molar mass of the hydrocarbon h.

Expert's answer

2C_{n}H_{2n+2}+3n+1 O2= 2n CO_{2}+2n+2H_{2}O

**1.**we find the amount of oxygen that reacts

75-12.5=62.5sm^{3 }

**2.**we can determine the proportion of hydrocarbons

2mol hydrocarbons 3n+1 oxygen

12.5sm^{3 }hydrocarbons 62.5sm^{3} oxygen

we get the value of n from the proportion

3n+1=62.5*2/12.5

3n+1=10

3n=9

n=3

hence the formula of the hydrocarbon is C_{3}H_{8}

**3.**we calculate the molar mass of C_{3}H_{8}

12*3+1*8=44g/mol

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