A 0.244 g sample of a compound of phosphorus and bromine, when dissolved in water, reacted to give a solution containing phosphorous acid and bromide ion. Addit

mass of sample : 0,244 g
(sample contains P and Br)
mass of AgBr : 0,508 g
The chemical formula of sample : .............. ?

Answered

Step 1
Make a reaction first between Br- and AgNO3.

Reaction
Br- + AgNO3 ------> AgBr + NO3-

Step 2
Determine the number of mole of AgBr

mole of AgBr : mass of AgBr / Mr AgBr
: 0,508 g / 188 g/mole
: 0,0027 mole

Step 3
Determine the number of mole of Br-. By using the coefficient of reaction Br- toward the coefficient of reaction AgBr.

mole of Br- : (c. Br- / c. AgBr) x mole of AgBr
: (1/1) x 0,0027 mole
: 0,0027 mole

Step 4
Determine mass of Br

mole of Br- equals mole of Br

mole of Br : mass Br / Ar Br
0,0027 mole : mass of Br / 80 g/mole
mass of Br : 0,0027 mole x 80 g/mole
: 0,216

Step 4
Determine mass of P in sample

mass of sample : m. P + m. Br
0,244 g : m. P + 0,216 g
mass of P : (0,244 - 0,216) g
: 0,028 g

Step 5
Determine mole of P

mole of P : mass P / Ar P
: 0,028 g / 31 g/mole
: 0,0009 mole

Step 6
Compared the number of mole of P toward mole of Br. So we are going to find the formula chemical of sample.

mole P : mole Br
0,0009 mole : 0,0027 mole
0,0009 : 0,0027
------------------------ / 0,0009
1 : 3

So, the formula chemical of sample is PBr3.

We want to know that PBr3 is a polar or a nonpolar. We can use electronegativity value of element. If the difference in electronegativity for the atoms in a bond is greater than 0.4. We consinder the bond polar.

In PBr3,
electronegativity value of P is 2.8
electronegativity value of Br is 2.16
E. value of PBr3 : 2.8 - 2.16
: 0.6
So, we can conclusion that PBr3 is a polar because PBr3 have electronegativity is greater than 0.4.

Source : wikipedia.com

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