7/22/2019 Determination of Ca and Mg in Limestone

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Determination of Ca and Mg in Limestone

Reagents required: KOH 5% solution, Buffer 10 for Mg, 0.01 M EDTA, Murexide Indicator,Solochrome Black

Spl prep:

1. Weigh 0.5 g of sample (Wt sample, W)

2. Add 10 ml of HCl (1+1)

3. Evaporate to dryness on a hotplate

4. Cool. Dissolve residue with 25 ml HCl (1+9), dilute to about 100ml and digest at low heat for15 mins.

5. Cool and make up to 250 ml in a volumetric flask. Let it settle or filter.

6. Suck up 25 ml aliquots for titrations.

CaO determination:

1. Add 4-5 ml of KOH 5%. Must be alkaline for color change, around 10-11 pH

2. Use Murexide as indicator.

3. Titrate against 0.01 EDTA. End point is purple.

Calc:

Avg Volume used, A ml.

Wt Ca in spl, C= A x 0.4008 x 250/25

% Ca in spl= C/W x 100%

% CaO in spl= %Ca x 56.08/40.08

% CaCO3 in spl= %Ca x 100.09/40.08

MgO determination:

1. Add 30 ml Buffer 10.

2. Use Solochrome black as indicator.

3. Titrate against 0.01 EDTA. End point is dark blue.

7/22/2019 Determination of Ca and Mg in Limestone

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Calc:

Avg Volume used, B ml.

Wt Mg in spl, D= B x 0.2431 x 250/25

% Mg in spl= D/W x 100%

% MgO in spl= %Mg x 40.32/24.32

% MgCO3 in spl= %Mg x 84.32/24.32

Note: CaCO3 +MgCO3 = around 99%