Sure! Let's go through the calculation steps one by one:
1) To determine the sodium carbonate content, we start by dissolving 2.0g of NaOH in 80ml of CO2-free water.
2) Next, we add 3 drops of phenolphthalein indicator to the solution. Phenolphthalein is a pH indicator that is colorless in acidic solutions and pink in basic solutions. We then titrate the solution with 1M HCl (hydrochloric acid) until the color changes from pink to colorless. The volume of HCl used in this step is recorded as V1 ml.
3) After the color change, we add 3 drops of methyl orange indicator to the solution. Methyl orange is another pH indicator that is yellow in acidic solutions and red in basic solutions. We continue the titration with 1M HCl until the color changes from yellow to red. The volume of HCl used in this step is recorded as V2 ml.
Now, let's move on to the calculations:
(%w/w)Na2CO3:
To calculate the percentage by weight of sodium carbonate (Na2CO3), we use the following formula:
(%w/w)Na2CO3 = (V2 x 10.6 x 1M) / 2.0g
Here, V2 represents the volume of 1M HCl used in the second titration with methyl orange indicator. We multiply V2 by 10.6 because sodium carbonate (Na2CO3) reacts with 1 mole of HCl to produce carbon dioxide (CO2), and the molar mass ratio between Na2CO3 and CO2 is 10.6.
We divide the product of V2 x 10.6 x 1M by 2.0g, which is the mass of NaOH used, to obtain the percentage by weight of sodium carbonate present in the NaOH sample.
(%w/w)Total alkali:
To calculate the percentage by weight of total alkali, we use the following formula:
(%w/w)Total alkali = ((V1+V2) x 4.0 x 1M) / 2.0g
Here, (V1+V2) represents the total volume of 1M HCl used in both titrations. We multiply (V1+V2) by 4.0 because NaOH reacts with 1 mole of HCl to produce 4 moles of total alkali (NaOH + Na2CO3).
Again, we divide the product of ((V1+V2) x 4.0 x 1M) by 2.0g to obtain the percentage by weight of total alkali present in the NaOH sample.
By following these calculations, you can determine the sodium carbonate content and total alkali in NaOH based on the volumes of HCl used in the titrations.