# In 1814, Sir Humphrey Davy and Michael Faraday collected samples of a flammable gas, A,from the ground near Florence in Italy.They analysed A which…

In 1814, Sir Humphrey Davy and Michael Faraday collected samples of a flammable gas, A,from the ground near Florence in Italy.They analysed A which they found to be a hydrocarbon. Further experiments were thencarried out to determine the molecular formula of A.

(a) What is meant by the term molecular formula? ………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………… ……………………………………………………………………………………………………………………..[2]

Davy and Faraday deduced the formula of A by exploding it with an excess of oxygen and analysing the products of combustion.

(b) Complete and balance the following equation for the complete combustion of ahydrocarbon with the formula CxHy

.CxHy + (x + y4)O2 ………………………….. + …………………………..[2]

(c) When 10 cm3 of A was mixed at room temperature with 50 cm3 of oxygen (an excess)and exploded, 40 cm3 of gas remained after cooling the apparatus to room temperatureand pressure.

When this 40 cm3 of gas was shaken with an excess of aqueous potassium hydroxide,KOH, 30 cm3 of gas still remained.

(i) What is the identity of the 30 cm3 of gas that remained at the end of the experiment? ……………………………………………

(ii) The combustion of A produced a gas that reacted with the KOH (aq). What is the identity of this gas? ……………………………………………

(iii) What volume of the gas you have identified in (ii) was produced by the combustion of A? ………………………….cm3

(iv) What volume of oxygen was used up in the combustion of A? ………………………….cm3 [4]

(d) Use your equation in (b) and your results from (c)(iii) and (c)(iv) to calculate the molecular formula of A.

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