AcidsandBases

Acids and bases in the real world. Batteries Pools Household cleaners Milk Sharpies Stomach acid/blood(base)

What are acids and bases? Brnsted-Lowry acids and bases

Acids donate H+ ions to another ion or molecule, which acts as a base.

Bases accept H+ ions from acid compounds.

So what does this look like in equation form?

HCl + NaOH ---> H2O+ NaCl Acid Base water Salt

pH and what it means. A rating of 0 on the pH scale indicates a

substance that is virtually pure acid, while a 14 rating represents a nearly pure base. A rating of 7 indicates a neutral substance.

pH just defines the concentrations of Hydrogen ions(H+) and hydroxide(OH-).

Aqueous Solutions An aqueous solution is a acid or base in

water. For example HCl poured into water.

What happens to the HCl?

Does the water affect the pH?

Aqueous Solutions cont.The chemical formula for water isH+ + OH- H2O

Does water affect any acids or bases when mixed?

So lets take a look at acids and bases. Activity 1

Color Changes with Acids and Bases You will be given three solutions

Sodium Hydroxide Vinegar Cream of Tartar

Cont. You will also be given two indicators.

BBT indicator Is naturally blue and when mixed with an

acid it will turn yellow Phenolphthalein

Is naturally clear and when mixed with a base it will turn pink.

Procedure 1. Label 4 empty clear plastic punch

cups cream of tartar, detergent, vinegar, and control.

2. Carefully pour 2 tablespoons of indicator solution into the control cup and fill with water.

3. Place the four labeled cups on a white piece of paper and fill with two spoons full of Lake Michigan Water.

Procedure cont. Students add acids and bases to the cups Cream of tartar

Use the scoop end of the straw to scoop up a small amount of cream of tartar.

Add the cream of tartar to the cream of tartar cup. Gently swirl to mix.

Sodium Hydroxide Use a dropper and drop 3 or 4 drops of sodium

hydroxide into the cup. Add the Sodium Hydroxide to the NaOH cup.

Gently swirl to mix. Vinegar

Use a dropper to add 2 or 3 drops of vinegar to the vinegar cup.

Gently swirl to mix.

Procedure cont. 5. Students add the phenolphthalein

indicator to each cup. Only one cup should change color.

6. Now add the excess control indicator to the remaining mixtures that did not change change.

So what were the acids and bases?

Can you think of a way to return the Yellow indicator solution from Activity 1 back to blue?

Activity 2: Neutralization what they might do to return the pink

indicator solution from Activity 1 back to clear?

Neutralization What should you add to the yellow cream

of tartar solution to change the color back to blue like the control?

What should you add to the pink Sodium Hydroxide solution to change the color back to clear?

Should you add a little bit of Sodium Hydroxide or cream of tartar, or a lot at once?

What will you do if the color does not quite change back to the original color after mixing the powder into the indicator solution?

How will you know when the solution has been neutralized?

Neutralization cont. Neutralize the cream of tartar solution

and the Sodium Hydroxide solution. Use a clean dropper to add a small amount

of Sodium Hydroxide to the cream of tartar and swirl. Observe the color. If needed, continue this process until the solution returns to blue.

Use a different clean toothpick/dropper to add a small amount of cream of tartar/vinegar to the Sodium Hydroxide solution and swirl. Observe the color. If needed, continue this process until the solution returns to clear/pink.

Disscussion Were you able to return the yellow and

pink indicator solutions back to their original colors?

What could you have done if the yellow indicator turned pink instead of blue?

What could you have done if the pink indicator turned yellow instead of clear?

How would you neutralize the vinegar solution?

Can a base neutralize an acid? Can an acid neutralize a base?

YesterdaySo the day before we looked at

neutralizing acids and bases with each other correct?

So today we are going to look at precise amounts of acid and base to neutralize the reaction.

So what I would like you to do today is to pick either the vinegar or the Sodium hydroxide to neutralize.

Remember which indicator you need to use.

If you choose vinegar what indicator do you need to use?

If you choose Sodium hydroxide what do indicator do you need?

Now choose one to start with before we continue.

Vinegar Sodium Hydroxide

Colors?

What color will you start and end with for vinegar?

What color will you start and end with for Sodium Hydroxide?

ProcedureVinegar Do two or three

trials ranging from 2 to 10 drops of vinegar. Then neutralize with Sodium Hydroxide.

Keep track of the drops you use.

Sodium Hydroxide

Do two or three trials ranging from 15 to 30 drops of sodium hydroxide. Then neutralize with vinegar.

Keep track of the drops you use.

Discussion What is the relationship between

the amount of acid in the solution and the number of drops of base it takes to return the solution back to neutral?

ResultsThe results come out to be for

every about every three drops of vinegar you need about 10 drops of Sodium Hydroxide.