Calculating Moles & Molarity of KHP & NaOH

In summary, the student put 0.737 grams of potassium biphthalate into a flask, then added 25 mL of distilled water, and titrated 34.06 mL of sodium hydroxide into it to reach an equilibrium point. To find the moles of the KHP, they divided the mass by the molar mass. They also calculated the number of moles of KHP based on this assumption. Finally, they asked the student for the molar mass of KHP, and explained that this number is not always consistent with the molecular mass of KHP.
  • #1
Prone17
7
0
what i did:

1) i put 0.737 g of KHP in a flask
2) then added ~25 mL of distilled water
3) and then titrated 34.06 mL of NaOH into it to get its equilibrium point,

how would i find: 1. the moles of KHP, and 2. the molarity of NaOH? and would the molar mass have any significance?

1. the moles of KHP
i thought i would turn .737 g into moles by dividing by the masses given in the periodic table (K=39.1g, H=1.01g, P=30.9g) = 71.08g in total

which gives 0.0104 moles of KHP

2. the molarity of NaOH

since I am pretty sure the mole ratio of NaOH and KHP is 1:1, i used 0.0104 moles of NaOH

M=moles/L
M= 0.0104/.03406
M= .305 M

is all this correct? and if so, why did they ask me for the molar mass of KHP (which i googled to be 204.22 g/mol) ? how is this even significant?

also, when doing the molarity part, would i have to take into consideration the 25mL of distilled water i added at the beginning of the experiment, or just the amount of NaOH i added?
 
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  • #2
Prone17 said:
what i did:

1) i put 0.737 g of KHP in a flask
2) then added ~25 mL of distilled water
3) and then titrated 34.06 mL of NaOH into it to get its equilibrium point,

how would i find: 1. the moles of KHP, and 2. the molarity of NaOH? and would the molar mass have any significance?

1. the moles of KHP
i thought i would turn .737 g into moles by dividing by the masses given in the periodic table (K=39.1g, H=1.01g, P=30.9g) = 71.08g in total

which gives 0.0104 moles of KHP

2. the molarity of NaOH

since I am pretty sure the mole ratio of NaOH and KHP is 1:1, i used 0.0104 moles of NaOH

M=moles/L
M= 0.0104/.03406
M= .305 M

is all this correct? and if so, why did they ask me for the molar mass of KHP (which i googled to be 204.22 g/mol) ? how is this even significant?

also, when doing the molarity part, would i have to take into consideration the 25mL of distilled water i added at the beginning of the experiment, or just the amount of NaOH i added?

I don't think the KHP you're using here has any phosphorus in it, rather it's an acid salt as you later discover
 
  • #3
sjb-2812 said:
I don't think the KHP you're using here has any phosphorus in it, rather it's an acid salt as you later discover

i'm not sure what that means. I'm just going by my lab book. i just know that the experiment was to titrate NaOH into KHP, and as far as i know, this was not a trick question. the bottle i took the KHP from said "KHP" on it.
 
  • #4
When you calculated the number of moles of KHP in
1. the moles of KHP
i thought i would turn .737 g into moles by dividing by the masses given in the periodic table (K=39.1g, H=1.01g, P=30.9g) = 71.08g in total

you made an assumption that the compound in question was literally KHP (one atom of potassium, one of hydrogen, and one of phosphorus). However, the molecular mass you got from google is not consistent with this. KHP can mean different things, and it's not totally your fault. It seems to me you are doing something similar to http://www.google.co.uk/search?q=ktp+standardization+naoh
 
  • #5
sjb-2812 said:
When you calculated the number of moles of KHP in


you made an assumption that the compound in question was literally KHP (one atom of potassium, one of hydrogen, and one of phosphorus). However, the molecular mass you got from google is not consistent with this. KHP can mean different things, and it's not totally your fault. It seems to me you are doing something similar to http://www.google.co.uk/search?q=ktp+standardization+naoh

yes i did assume that. but then i realized that to find the moles of KHP (part 1 of my question), i would divide the mass of KHP (0.737 g) by the molar mass of KHP (204.22 g/mol). is this correct? and yes, that link is exactly what i did in the experiment.
 
  • #7
Just a guess: Are you abbreviating Potassium Biphthalate with "KHP"?
 

FAQ: Calculating Moles & Molarity of KHP & NaOH

What is the purpose of calculating moles and molarity in the KHP and NaOH experiment?

The purpose of calculating moles and molarity is to determine the concentration of a solution and the number of moles of a substance present in a given volume of the solution. This is important in the KHP and NaOH experiment because it allows us to accurately measure and control the amount of reactants used in the reaction.

How do you calculate the number of moles of KHP in a given sample?

The number of moles of KHP (potassium hydrogen phthalate) can be calculated by dividing the mass of the sample by its molar mass. The formula for this calculation is: moles of KHP = mass of sample (g) / molar mass of KHP (g/mol).

3. What is the formula for calculating the molarity of a solution?

The formula for calculating molarity is: molarity (M) = moles of solute / volume of solution (L). In the KHP and NaOH experiment, the moles of the solute (KHP) can be calculated as described in question 2, and the volume of the solution can be measured using a graduated cylinder or burette.

4. How do you determine the concentration of NaOH using the molarity of KHP?

In the KHP and NaOH experiment, the molarity of NaOH can be determined by using the molarity of KHP and the balanced chemical equation for the reaction. Since the reaction between KHP and NaOH is 1:1, the moles of NaOH will be equal to the moles of KHP used. Therefore, we can use the molarity of KHP to calculate the molarity of NaOH.

5. Why is it important to perform multiple trials when calculating moles and molarity in the KHP and NaOH experiment?

Performing multiple trials allows for more accurate and reliable results. Due to potential errors in measurement and human error, the results from a single trial may not be precise. By performing multiple trials and calculating an average, we can reduce the impact of these errors and obtain more accurate data.

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