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Warmup 2/13/14

Warmup 2/13/14. If you have 10 moles of a strong acid, how many moles of strong base do you need to cancel it out?. Objective Tonight’s Homework. To learn how we can measure the concentration of an acid or base through experimentation. be ready to run your lab tomorrow. Notes on Titration.

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Warmup 2/13/14

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  1. Warmup2/13/14 If you have 10 moles of a strong acid, how many moles of strong base do you need to cancel it out? Objective Tonight’s Homework To learn how we can measure the concentration of an acid or base through experimentation be ready to run your lab tomorrow

  2. Notes on Titration Let’s say we have a solution that we know is acidic, but we don’t know its pH. How can we find it?

  3. Notes on Titration Let’s say we have a solution that we know is acidic, but we don’t know its pH. How can we find it? Scientists determine this with an experiment called a titration. Titrations involve 2 additional things: 1) A base of known concentration (preferably a strong base that ionizes completely) 2) A pH indicator solution that will change color at a known pH.

  4. Notes on Titration In our unknown acid, we have the following: ?? moles H+ ____ known number of liters If we can find how many moles of H+ we have, we can get the pH. So how do we get this?

  5. Notes on Titration In our unknown acid, we have the following: ?? moles H+ ____ known number of liters If we can find how many moles of H+ we have, we can get the pH. So how do we get this? We find this out by adding a base to our solution until it’s neutral. If we know how many moles of OH- this takes, we can find how many moles of H+ we started with. Essentially: Moles of OH- used = moles of H+ originally there

  6. Notes on Titration To find how many moles of OH- it takes to neutralize the solution, we usually add our strong base one drop at a time to the acid until our indicator changes color, showing us that the solution is now neutral.

  7. Notes on Titration Let’s go into more depth with an example: An unknown acid is in solution in 3 L of water. A student adds 2 M NaOH 1 drop at a time until the solution neutralizes. If each drop is 0.3 mL and it takes 144 drops to neutralize, what was the pH of the original acid?

  8. Notes on Titration Let’s go into more depth with an example: An unknown acid is in solution in 3 L of water. A student adds 2 M NaOH 1 drop at a time until the solution neutralizes. If each drop is 0.3 mL and it takes 144 drops to neutralize, what was the pH of the original acid? Our NaOH is a strong base, so every OH- should separate. So moles NaOH = moles OH-. So… moles OH- = [NaOH] • liters NaOH = 2 • (0.3mL • 144) • = 0.0864 mol OH- 1 L _ 1000 mL

  9. Notes on Titration If we used 0.0864 mol OH-, it means we also had 0.0864 moles H+ since we neutralized them. We have just one last step: [H+] = [H+] = [H+] = 0.0288 We can then get pH from this: pH = -log[H+] pH = 1.54 moles H+ liters H+ 0.0864 moles H+ 3 liters

  10. Practice Let’s take a look at problems 24, 25, and 26 on page 619.

  11. Titration Lab Tomorrow, we’re going to do a lab on titration. Your job today is to find the volume of 1 drop from our titration setups. We need to know this so we can calculate volumes precisely.

  12. Exit Question #20 How many mL of 1 M NaOH do we need to cancel out 1 L of 1 M HF? a) 1 b) 10 c) 100 d) 1000 e) Not enough information f) None of the above

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