3. Number of Fe atoms in 100 g Haemoglobin if it contains 0.33% Fe. (Atomic mass of Fe = 56)
(1) 0.035 x 1023
(2) 35
(3) 3.5 x 1023
(4) 7 108
​

(1) 0.035 × 10²³

Explanation:

Step 1: Calculate the mass of Fe in 100 g of Haemoglobin

Haemoglobin contains 0.33% Fe, that is, there are 0.33 g of Fe per 100 grams of Haemoglobin.

100 g Hb × 0.33 g Fe/100 g Hb = 0.33 g Fe

Step 2: Convert 0.33 g of Fe to moles

We will use the molar mass of Fe (55.85 g/mol).

0.33 g × 1 mol/55.85 g = 5.9 × 10⁻³ mol

Step 3: Convert 5.9 × 10⁻³ moles of Fe to atoms

We will use Avogadro's number.

5.9 × 10⁻³ mol × 6.02 × 10²³ atoms/1 mol = 3.5 × 10²¹ atoms (= 0.035 × 10²³)

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"