A student needs to determine by titration with NaOH the precise %KHP in an unknown sample that is thought to contain approximately 50%KHP. Approximately what mass of sample should the student use in order to use about 20mL of 0.1005 M NaOH to reach the endpoint of the titration?
please help me.
First, determine the approximate number of grams of KHP.
moles = M x L = 0.1005M x 0.020 L = ?? moles NaOH.
moles KHP = moles NaOH.
grams KHP = moles KHP x molar mass KHP = xx grams KHP.
%KHP = (grams KHP/mass sample)*100 = 50
You know grams from the calculations above, substitute into the percent equation; the only unknown is mass sample. [Note: In the real world, especially where an analyst does many titrations in a day, the mass of sample is actually weighed out (to four places) so that the reading on the buret corresponds to the percent X in the sample (done for other titrations in addition to acidity). Saves a lot of time on calculations. Read the buret and write down the percent in the lab book. This coupled with automatic fill and zero burets saves even more time. And in industry, time is money.]
thank you very much for your help!
0.286
.822
When rearranged, its
.411g KHP x 100
-------------------- = mass
50
Which equals .822
To determine the precise %KHP in the unknown sample through titration, you need to calculate the mass of the sample that should be used. Here's how you can do it:
Step 1: Determine the moles of NaOH used.
Given:
- Volume of NaOH used (V_NaOH) = 20 mL = 0.02 L
- Concentration of NaOH (C_NaOH) = 0.1005 M
Moles of NaOH = Volume (L) x Concentration (M)
Moles of NaOH = 0.02 L x 0.1005 M
Step 2: Determine the initial moles of KHP.
Given:
- Assumed %KHP in the unknown sample = 50%
Assuming 100 g of the sample, the mass of KHP = 50 g (50% of 100 g)
Molar mass of KHP = 204.23 g/mol
Moles of KHP = Mass (g) / Molar mass (g/mol)
Moles of KHP = 50 g / 204.23 g/mol
Step 3: Use the stoichiometry of the balanced equation to relate the moles of KHP to the moles of NaOH.
The balanced equation for the reaction between KHP and NaOH is:
KHC8H4O4 (KHP) + NaOH → KNaC8H4O4 + H2O
From the balanced equation, it can be seen that 1 mole of KHP reacts with 1 mole of NaOH.
Step 4: Determine the moles of KHP that reacted.
Moles of KHP reacted = Moles of NaOH used (from Step 1) x Stoichiometric ratio
Moles of KHP reacted = (0.02 L x 0.1005 M) x 1
Step 5: Calculate the mass of KHP in the unknown sample.
Mass of KHP = Moles of KHP reacted x Molar mass of KHP
Mass of KHP = (0.02 L x 0.1005 M) x 1 x 204.23 g/mol
Step 6: Determine the mass of the sample.
To find the mass of the sample that should be used, you need to rearrange the equation from Step 5 as follows:
Mass of Sample = Mass of KHP / (Assumed %KHP in decimal form)
Mass of Sample = [(0.02 L x 0.1005 M) x 1 x 204.23 g/mol] / 0.50
Now, you can plug in the values into the equation to calculate the mass of the sample.
Note: If the assumed %KHP in the unknown sample is different, make sure to adjust the calculation accordingly.
I hope this helps!