Solve Backtitration Problem: Find mL of NaOH Used

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In summary, the conversation discusses finding the amount of NaOH used in a back titration, starting with a 0.6000 g sample of K2CO3 dissolved in solution A. A 20.00 mL aliquot of solution A is mixed with 20.00 mL of 0.1700 M HCl, and the resulting solution is titrated with 0.1048 M NaOH. The excess HCl amount from the first reaction is needed to solve the equation.
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orchidee7
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Please post homework and homework like problems in the homework forum
I'm stuck on how to find how many ml of NaOH were used in a back titration.

A 0.6000 g sample of K2CO3 (138.2055 g/mol) is dissolved in enough water to make 200.0 mL of solution A. A 20.00 mL aliquot of solution A is taken and put into an Erlenmeyer flask. To the flask is added 20.00 mL of 0.1700 M HCl:

K2CO3(aq) + 2HCl(aq)2KCl(aq) + H2O(l) + CO2(g)

The resulting solution is then titrated with 0.1048 M NaOH.

NaOH(aq) + HCl(aq) → H2O(l) + NaCl(aq)

How many mL of NaOH are used? (24.16)

I have:
0.6000gK2CO3 x (1/138.2055gK2CO3) x (1/.200ml) = 0.021707 M K2CO3.
0.170M HCl x (1/0.04ml) = 0.0034 mol HCl and 0.0034 mol NaOH (1:1 ratio)

From here I don't know what to do to find the ml of NaOH required to solve the equation. Could anybody show me how or give me some hints? Thank you.
 
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  • #2
What was the amount of the excess HCl (first reaction)?
 

What is a back titration?

A back titration is a type of titration used in analytical chemistry to determine the concentration of an unknown substance by reacting it with an excess of a known reagent. This excess is then titrated with a second reagent to determine the amount of excess reagent and, subsequently, the amount of the unknown substance.

How do you solve a back titration problem?

To solve a back titration problem, you will need to follow these steps:1. Determine the initial amount of the unknown substance.2. React the unknown substance with an excess of a known reagent.3. Titrate the remaining excess reagent with a second reagent.4. Use the results of the titration to calculate the amount of excess reagent.5. Subtract the amount of excess reagent from the initial amount to determine the amount of unknown substance.

Why is back titration used?

Back titration is used when the reaction between the unknown substance and the known reagent is slow or difficult to detect. It is also used when the unknown substance is present in a small amount or when it is insoluble in the solvent used for the titration. Back titration allows for more accurate and precise results in these situations.

What is the purpose of finding the mL of NaOH used?

The purpose of finding the mL of NaOH used in a back titration problem is to determine the concentration of the unknown substance. By knowing the amount of NaOH used, you can calculate the amount of excess reagent and, subsequently, the amount of the unknown substance present in the sample.

What are some common sources of error in a back titration?

Some common sources of error in a back titration include inaccuracies in measuring the volume of the reagents, impurities in the reagents, incomplete reaction between the unknown substance and the excess reagent, and human error in reading the titration endpoint. It is important to minimize these errors to obtain accurate results.

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