Answer to Question #182762 in General Chemistry for Zane okon

Question

1. Give reasons why the compound 3-bromo-3ethyl heptane gives no reaction with potassium hydroxide but bromo-propane does?
2. A 3.1 sample of an unknown organic gas molecules composed of carbon, hydrogen and oxygen undergoes complete combustion to produce 4.4g CO2 and 2.7g H20. Calculate the empirical and molecular formular of the gas molecule if the molar mass is 62g/mol
3. Nitrogen in organic compound is tested by the addition of few drops of saturated iron (III) sulphate solution to a small portion of sodium fusion filtrate. Dilute hydrogen tetraoxosulphate(Vl) is then added to the later solution leading to the formation of a Prussian blue colour or ppt. signaling the presence of nitrogen. Show these steps using equations and nameyour final product.

Answer 1

1. When ethyl bromide reacts with aqueous KOH, it undergoes hydrolysis.The lone pair on O in OH attracts the hydrogen on the beta carbon( the carbon next to the carbon which has the bromide group) and the potasssium cation attracts the bromide group. The product is ethene and the by products are water and KBr.

2. Amounts of CO₂ and H₂O in moles are:

$n(CO_2)=\frac{4.4g}{44g/mol}=0.1mol$

$n(H_2O)=\frac{2.7g}{18g/mol}=0.15mol$

The mass of O₂ can also be determined directly since the total mass of reactants is always equal to the total mass of products:

$m(O_2)=4.4+2.7-3.1=4.0g$

The amount of O₂ in moles:

$n(O_2)=\frac{4.0g}{32g/mol}=0.125mol$

Therefore, the O₂ : CO₂ : H₂O molar ratio is 0.125 : 0.1 : 0.15, which equals 5 : 4 : 6 as the lowest whole number ratio.

Now the overall equation can be written:

nC_xH_yO_z + 5O₂ --> 4CO₂ + 6H₂O

For the equation to become balanced, there should be 4 carbon atoms, 12 hydrogen atoms, and 4 oxygen atoms on the left side, in other words, x : y : z = 4 : 12 : 4. The lowest whole number ratio of this (1 : 3 : 1) determines the empirical formula, which is CH₃O. To calculate the molecular formula, the molar masses of the empirical formula unit and the unknown compound should be compared:

$M(CH_3O)=12+3\times1+16=31g/mol$ , which is 2 times less than the actual molar mass (62 g/mol). Therefore, the subscripts of the empirical formula should be multiplied by 2 giving C₂H₆O₂.

Answer:

Empirical formula CH₃O

Molecular formula C₂H₆O₂

3. A prussian blue colouration indicates the presence of nitrogen in the compound. If nitrogen is present in the compound, the sodium extract would contain sodium cyanide formed during fusion. On adding the required reagents, sodium cyanide reacts to form ferric-ferrocyanide which has prussian blue colour.