Calculate the mass of CaO:

The mass of CaO (m₃) created could be calculated using following Eq. (10.8)

m₃ = 1.27 (m₁ - m₂)   ... (10.8)

This equation can be acquired as follows:

The CaO is formed through the evolution of CO₂ on the decomposition of CaCO₃,

CaCO₃ (s) → CaO (s) + CO₂ (g)

M_r   100.1       56.1                 44

From the above equation 1mole of CaCO₃ gives 1 mole of CO₂ and 1mole of CaO. Thus, moles of CO₂ in the given examples = (m₁ - m₂ )/ M _r (CO ₂ ) and this is equivalent to moles of CaO formed

Therefore the amount of CaO must be, m₃ = (m₁ - m₂  )/ 44 × M _r (CaO)

where, M_r(CaO) is the associative molar mass of CaO.

m₃ = (m₁ - m₂ ) /44 × 56.1g

m₃ = 1.27(m₁ - m₂) g

We know the mass of residue left, i.e., m₂, the mass of MgO (m₄) can be calculated.

m₄ = m₂ - m₃

Here m₃ is the mass of CaO formed that is equal to 1.27 (m₁ - m₂). Thus

m₄ = m₂ - 1.27 (m₁ - m₂)

Mass of the Ca (m_ca) in the original sample can also be related to m₁ and m₂ by the following formula

m_ca = 0.91 (m₁ - m₂) This can be obtained as follows:

You know amount of Ca in CaCO₃ and CaO will be equal in moles, thus amount of Ca in

m_Ca =  m₃ ×Ar(Ca)/Mr(CaO) = 1.27 (m₁- m₂ ) ×Ar(Ca)/Mr(CaO)

where, Ar(Ca) and Mr (CaO) are the associative atomic mass and relative molar mass of Ca and CaO, respectively. Therefore,

= 1.27 (m₁ - m₂) × 40/56 = 0.91 (m₁ - m₂)

Similarly, mass of magnesium in the original sample can be related to m₁ and m₂:

Thus, the mass of Mg in original sample (mMg)

= (mass of residue - mass of CaO)× Ar (Mg)/M r (MgO)

m_Mg =(m₂  - m₃ ) × Ar (Mg)/ M r (MgO) =   (m₂ - m₃ ) 24.3/40.3

m_Mg  =  0.60 (m₂ - m₃)