To determine the sodium carbonate content & total alkali in NaOH, the following steps were performed:-
1) 2.0g of NaOH was dissolved in 80ml of CO2 free water.
2) 3 drops of phenolphthalein indicator were added and the solution was titrated with 1M HCl. Colour changed from pink to colourless.(V1 ml of HCl used)
3) 3 drops of methyl orange indicator were then added and the titration with 1M HCl was continued. Colour changed from yellow to red.(V2 ml of HCl used)
Calculations:
(%w/w)Na2CO3
= (V2 x 10.6 x 1M) / 2.0g
(%w/w)Total alkali
= ((V1+V2)x 4.0 x 1M) / 2.0g
Please explain how the calculation steps are derived?
Thanks.
Na2CO3 is determined from the second part of the titration. The equation is
NaHCO3 + HCl ==> NaCl + CO2 + H2O
mass Na2CO3 = moles Na2CO3 x molar mass Na2CO3.
moles Na2CO3 = MHCl x LHCl
Therefore, mass Na2CO3 =
MHCl x LHCl x molar mass Na2CO3 and
percent Na2CO3 is (mass Na2CO3*100)/2.0 g.
The second one is similar.
V1 titrates all the OH and 1/2 the carbonate half way (to bicarbonate).
V2 titrates the bicarbonate to carbonate (half way, that is); therefore, V1 + V2 titrates all the oH and all the carbonate.
So we have the same 100/1000 factor (100 converts to percent and 1000 converts from mL of V1+V2 to L of V1 + V2), then 40 (the molar mass NaOH) divided by 10 = 4.0.
What your prof has done is to substitute 1 M HCl for the titrant, mL for L HCl (but note mL must be divided by 1000 to convert to L), then we multiply by 100 to convert to percent. That gives us a 100/1000 factor which is 1/10 and 1/10 x molar mass Na2CO3 (which is 106) gives 10.6.
if i spill a little of sodium carbonate after it is weighed, will it affect my the percentage of sand that i calculate at the end of the experiment
The calculation steps are derived based on the principles of acid-base titration and the reactions involved in the titration process.
Step 1:
In this step, 2.0g of NaOH is dissolved in 80ml of CO2-free water. This step is done to prepare a solution of NaOH for further analysis.
Step 2:
In this step, 3 drops of phenolphthalein indicator are added to the NaOH solution, and the solution is titrated with 1M HCl. The phenolphthalein indicator is colorless in acidic solutions and pink in basic solutions. As NaOH is a strong base, it reacts with HCl to form water and sodium chloride. The reaction can be represented as follows:
NaOH + HCl → NaCl + H2O
The endpoint of the titration is reached when all the NaOH has reacted with the HCl and the solution turns colorless. The volume of HCl (V1 ml) used to reach the endpoint is recorded.
Step 3:
In this step, 3 drops of methyl orange indicator are added to the solution remaining from Step 2, and the titration with 1M HCl is continued. Methyl orange indicator is yellow in acidic solutions and red in basic solutions. The remaining NaOH in the solution reacts with the additional HCl. The reaction can be represented as follows:
NaOH + HCl → NaCl + H2O
The endpoint of the titration is reached when all the remaining NaOH has reacted and the solution turns red. The volume of HCl (V2 ml) used in this second titration step is recorded.
Calculations:
The calculations derive the weight percent of sodium carbonate (%w/w Na2CO3) and the weight percent of total alkali (%w/w Total alkali) in the original 2.0g of NaOH.
For %w/w Na2CO3:
The molar mass of Na2CO3 (sodium carbonate) is 106 g/mol. The equation used for the calculation is:
(%w/w)Na2CO3 = (V2 x 10.6 x 1M) / 2.0g
In this equation, V2 represents the volume of HCl (in mL) used in the second titration step. The factor of 10.6 is derived from the molar mass of Na2CO3 divided by the molar mass of NaOH (40 g/mol / 2 g/mol).
For %w/w Total alkali:
The equation used for the calculation is:
(%w/w)Total alkali = ((V1 + V2) x 4.0 x 1M) / 2.0g
In this equation, V1 represents the volume of HCl (in mL) used in the first titration step. The factor of 4.0 is derived from the molar mass ratio of NaOH to Na2CO3 (4 g/mol NaOH / 106 g/mol Na2CO3).
By plugging in the values for V1 and V2, the weight percent of sodium carbonate and total alkali can be calculated.
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.