An organic compound is found to contain 58.8% carbon, 9.8% hydrogen and 31.4% ox

Question

An organic compound is found to contain 58.8% carbon, 9.8% hydrogen and 31.4% oxygen by weight. Find the empirical formula.

(ii) The relative molecular mass of the organic compound in parent

(i) is 102 amu, find the molecular formula from the empirical formula.

(iii) Explain what is a hydrogen bond or hydrogen bonding, and state which elements undergo hydrogen bonding with H.

(iv) Write a chemical formula for the named chemicals (a)-(d). In each case also show the charge on the cation and anion. For the chemical formulas (e)-(h) write the name of the compound

(a) Calcium oxide (e) AlCl3 (

b) Lithium Bromide (f) Ca3(PO4)2

(c) Sodium Sulfate (g) MgCl2

(d) Sodium hydroxide (h) KI

If anyone can give proper well worked out, easy to understand solutions than that would be muchly appriciated!

Thanks

Explanation / Answer

Answering (i) and (ii)

Moles of carbon atom = 58.8/12 = 4.9 = ~5 (rounding to the nearest integer)

Moles of hydrogen atom = 9.8/1 = 9.8 = ~10 (rounding to the nearest integer)

Moles of oxygen atom = 31.4/16 = 1.96 =~ 2 (rounding to the nearest integer)

Empirical formula = C5H10O2

Now the empirical formula gets you a molecular mass of = 12 x 5 + 1 x 10 + 16 x 2 = 102 amu

Therefore, in this case, empirical formula = molecular formula = C5H10O2

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Answering (iii)

Hydrogen bonding occurs when hydrogen attached to an elctronegative atom involves in electrostatic interaction with an electronegative atom having lone pairs.

For example: H2O has two hydrogen atoms bound to an oxygen atom which is highly electronegative. The electrons involve in the O-H bond stays close to oxygen due to its high electronegativity. Thus the H atoms get partial positive charge. These partial positively charged hydrogen on one H2O molecule interacts with the lone pairs of oxygen on other H2O molecules. The lone pairs can be thought of as negatively charged electron cloud.

The elements that are known to undergo hydrogen bonding with hydrogen are : F (fluorine), O (oxygen) and N (nitrogen).   Cl (chlorine) and S (sulfur) can also form H-bonds to some extent.

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Answering (iv)

(a) Calcium oxide = CaO = Ca2+ O2-

(b) Lithium bromide = LiBr =Li+1 Br -1

(c) Sodium sulfate = Na2SO4 = Na2+1 SO42-

(d) Sodium hydroxide = NaOH = Na+1 OH-1

(e) AlCl3 = Aluminium chloride

(f) Ca3(PO4)2 = Calcium phosphate

(g) MgCl2 = Magnesium chloride

(h) KI = Potassium iodide

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