Chemistry Spring 2013
Name: ______Per: ______
Unit 10 Homework and Lab Packet
Acids and Bases (Ch. 19)
Acids-Bases I / Acids-Bases II / Acids-Bases III / Acids-Bases IV / Identifying Acids and Bases“Acids and Bases” song / Making Soap / Comparing Antacids / Household Acids and Bases
Unit 9 Homework Grade ______
Overall Objective: Understand the purpose of acids and bases in chemistry and in everyday life.
At the end of the unit you should be able to:
· List the general properties of acids and bases
· Understand the Arrhenius definition of an acid and base
· Identify the Arrhenius acid and base that react to produce a given salt
· Write formulas for, and name, acids and bases
· State the color of the following indicators in a solution of a given pH: phenolphthalein, methyl red, and bromthymol blue
· Perform stoichiometry calculations that involve acid-base titrations
· Iowa Model Core
o Understand and apply knowledge of the structure and properties of matter.
o Understand and apply knowledge of chemical reactions
Acid-Base 1: Identifying Acids and Bases
Indicate whether each of the following properties corresponds to an acid or to a base.
1) sour taste / ______2) slippery feel / ______
3) turns blue litmus paper red / ______
4) pH greater than 7 / ______
5) Produces H+ ions in water / ______
6) bitter taste / ______
7) Turns red litmus paper blue / ______
8) Produces OH- ions in water / ______
Key Concept:
When an acid and base react together, they neutralize to form water (H2O) and a salt.
Use this information and your notes to answer the following questions.
1. Identify the Arrhenius acid and Arrhenius base in each of the following neutralization reactions.
a. HI + NaOH à NaI + H2O
b. LiOH + HC2H3O2 à LiC2H3O2) + H2O
c. 2 HClO3 + Ba(OH)2 à Ba(ClO3)2 + 2 H2O
d. H2SO4 (aq) + 2 KOH(aq) à K2SO4 (aq) + 2H2O(l)
e. LiOH + HF à LiF + H2O
f. Ca(OH)2 + H2SO4 à CaSO4 + 2 H2O
Acid-Base II: Naming acids and writing formulas
Binary acids
1) These are compounds containing hydrogen and a nonmetal
2) Formulas always begin with H
3) Named by using the prefix hydro- before the nonmetal stem and adding the suffix –ic acid
Example
Give the name for HF, a binary acid.
Solution
We name a binary acid as hydro- plus nonmetal stem plus –ic acid.
HF contains the nonmetal fluorine, and we construct its name as follows:
hydro + fluor + ic acid.
HF is named hydrofluoric acid.
Polyatomic Acids
These acids contain more than two different elements.
1) “If I –ate it, I’d say –ic.
2) NO HYDRO-
Example:
Name the acid with formula HNO3
See that there’s more than two different elements and the polyatomic ion (NO3) is named nitrate. Change –ate to –ic and add acid.
Nitric acid
3) If the polyatomic ends in –ite, like NO2 (nitrite), change ending to –ous.
Example:
Name the acid with formula HNO2
See that the polyatomic ion (NO2) is named nitrite. Change –ite to –ous and add acid.
Nitrous acid
Problems
Give the name for the following binary acids:
1) H2S
2) HBr
3) HI
4) HCl
Provide the formula for each of the following binary acids:
5) hydrosulfuric acid
6) hydroselenic acid
Give the name for the following polyatomic acids
7) HClO3
8) H3PO4
9) H2SO4
10) H2SO3
Provide the formula for each of the following polyatomic acids
12) carbonic acid (it’s in Pepsi)
13) nitrous acid
Acid-Base III: Determining the acid and base
Key Concept:
When an acid and base react together, they neutralize to form water (H2O) and a salt
1. Determine the acid and base that were neutralized to produce each of the following salts.
a. Sodium fluoride, NaF
Plan: one product is this salt, NaF. The other HAS to be water (see “key concept”). Draw the yield sign with these as your products.
à NaF + H2O
Next: the hydrogen ion (H+) came from the acid and the (OH-) came from the base. These formed the water (H2O). You now know one half of the acid, and one half of the base. Figure out what ion from NaF will bond with the positive (H+) and the negative (OH-). Remember Paula Abdul.
H___ + ____OH à NaF + H2O
Repeat these two steps to complete the next three questions.
b. Magnesium iodide, MgI2
c. Calcium nitrate, Ca(NO3)2
d. Lithium carbonate, Li2CO3
2. Determine the acid and base that were neutralized to produce each of the following salts. Write the formula for the salt before answering.
a. Potassium bromide
b. Barium chloride
c. Cobalt (II)sulfate
d. Sodium phosphate
3. Complete and balance the following neutralization reactions.
Plan: Reread the “Key Concept” on the last page.
a. HNO3(aq) + Ca(OH)2(aq) à
b. H2CO3(aq) + Ba(OH)2(aq) à
c. KOH(aq) + HNO3 (aq) à
d. Ba(OH)2(aq) + HCl(aq) à
e. NaOH(aq) + H3PO4(aq) à
f. Ca(OH)2(aq) + H3PO4(aq) à
Acid Base IV: Indicators
Using p.602, state the color of the acid-base indicator in each of the following solutions
1) A solution at pH 3 contains a drop of methyl red.
2) A solution at pH 8 contains a drop of bromthymol blue
3) A solution at pH 11 contains a drop of phenolphthalein
4) A solution at pH 7 contains a drop of methyl red
5) A solution at pH 5 contains a drop of bromthymol blue
6) What is the color of bromthymol blue indicator in a solution of pH7?
7) What is the color of methyl red indicator in a solution of pH5?
8) What is the color of phenolphthalein in pure water?
Identifying Acids, Bases, and Salts
The following table contains a list of compounds that can be classified as acids, bases, or salts.
1. Decide what type of substance each compound is and fill in the appropriate space in the column.
2. Base your answer on the compound's formula and on the one piece of information supplied about either its pH or its reaction with an indicator.
3. Fill in any remaining blank spaces for that compound.
To help you become familiar with these substances, information about the use of each compound has been provided. You will probably find this information quite interesting.
Acid, Base, / Color in / Color in / ApproximateCompound / or Salt / Litmus / Phenolphthalein / pH
H3PO4
found in some cola / red
beverages
Ca(OH)2
slaked lime / above 7
used for treating soil
CaSO4 / about 7
used in plaster of Paris
H2CO3
produced in human body / clear
from metabolism of fats
and sugars
Na3PO4
used in some water / no effect
softeners
H2S / below 7
odor of rotten eggs
H2SO3 / red
component in acid rain
Mg(OH)2 / blue
found in milk of magnesia
NH4Cl / about 7
used in batteries and / (slightly below)
Dry cells
“Acids and Bases “
Acids and bases, in life you have a place
Acids have a hydrogen, hydroxide for a base
Acids five off H+ when in water they are stirred
Forming H3O+, hydronium’s the word
The more hydroniums there are, the lower pH gets
All because the silly acid had to go get wet!
Reactive metals like Ca and Fe oxidize
When reacted with an acid they can really shrink in size
Gaseous hydrogen is formed as well as salt in fact
But metals like Au, Ag and Cu won’t react!
Acids and bases, in life you have a place
Acids have a hydrogen, hydroxide for a base
Bases yield hydroxide, OH- how we write
When dissolved in water, and disappear from sight
The more hydroxide ions, the higher pH slopes
The more slippery it feels as it turns your skin to soap!
Fats are hydrolyzed by bases, turns them into soap
Which can be fashioned into bars or dangled from a rope
Bases form when active metals in H2O are placed
Sodium forms from sodium hydroxide, a strong base!
Acids and bases, in life you have a place
Acids have a hydrogen, hydroxide for a base
Put the two together and you get some real neat stuff
It’s called neutralization, I can never get enough
It makes water molecules and salt with no regrets
Titration’s what you call it when you mix them with burets
MaVa = MbVb can be used to calculate
Concentrations of an acid or a base when you titrate
Just remember that Ma or Mb will get multiplied
By the number of each ion by which they’re identified!
Acids and bases, in life you have a place
Acids have a hydrogen, hydroxide for a base
Making Soap
Purpose
Many years ago, American families made the soap used in their home. They saved their cooking fat and mixed it with lye (sodium hydroxide). Heating the mixture formed lye soap.
Procedure
1. Add 10 ml oil (or 10g fat) with 10 ml ethyl alcohol in a flask.
2. Heat the mixture until hot.
3. Add 10 ml of 30% sodium hydroxide, NaOH.
CAUTION: 30% NaOH is very caustic and will
damage skin tissue. If you come in contact with it,
rinse immediately for several minutes with
large amounts of water.
4. Heat and stir the mixture until no more alcohol odor is detected.
Remove from heat.
5. Add 20 ml of distilled water and stir mixture until uniform. Let it cool.
6. Pour the mixture into a beaker containing 100 ml saturate salt (NaCl) solution. Stire as you add the solution.
7. Filter the solid that forms. This is your soap. Place in a small metal tin to shape it.
8. Leave the soap on a paper towel to dry overnight. You will test it tomorrow.
Postlab
1. Moisten a small piece of your soap. Test it with pH paper. What do you observe?
2. Test the filtrate with pH paper. What do you observe?
3. Place a small piece of your soap in 10 ml of distilled water. Shake 10 times.
a) Describe the suds produced.
b) Describe the appearance of the water.
4. Repeat step #3 using tap water.
a) Describe the suds produced.
b) Describe the appearance of the water.
5. What do the results of step 3 and 4 tell us?
Clean all glassware and lab tables.
Discard soap in the wastebaskets.
Comparison of Antacids Lab
Introduction:
All of us have been affected (or will be affected) one time or another by indigestion. Indigestion is often caused by excess stomach acid. Popular stomach remedies, or antacids, claim to remove the symptoms of acid indigestion by neutralizing excess stomach acid (HCl).
In this investigation, you will test the effectiveness of several commercial antacids by determining whether the antacid will neutralize a given volume of hydrochloric acid (HCI).
Materials:
Small beaker Medicine dropper 0.1 M HCl
Methyl orange indicator Stirring rod Mortar and pestle
4 Test Tubes
Several different commercial antacids (Rolaids, Tums, Maalox, Alka Seltzer)
Procedure:
1. Pour 5 mL of 0.1M HCl into 4 test tubes.
2. Add 23 drops of methyl orange indicator into each test tube. Record the color in your data table.
3. Obtain four different antacids from your teacher. Write the names of these in your data table. Be sure to note the active ingredient(s) on the container and record that too.
4. Mass 1 gram of antacid in your 100 mL beaker. Dissolve it with 5.0 mL of deionized water. Add the water slowly while stirring until dissolved.
5. Fill a dropper with an antacid and add it drop by drop to one of the test tubes stirring after each drop. Stop after you see a color change. In your data table under the name of the antacid, record the number of drops it took to change the color.
6. Repeat step 5 with the other 3 antacids and record your results. Be sure to thoroughly clean your beaker each time to avoid contamination. Rinse with deionized water.
Data:
Brand Name / Active Ingredient(s) / Color of HCl with Methyl Orange Before / Final Color of HCl After Reaction / # of drops of Antacid usedQuestions (to be answered in lab notebook)
1. Is the addition of an indicator a chemical or physical reaction? Justify your answer.
2. How would you classify the addition of antacid to acid? Ex: Synthesis, Decomposition, etc. Explain your choice
3. Which antacid do you think is the most effective? least effective? Explain why.
4. What of the ingredient(s) do you think were the active neutralizing agent for each of the antacids? What makes you think so?
5. Some of the antacids had more than one active ingredient. Were these antacids more effective than the antacids with only one active ingredient? Explain.
6. Pick two of the active ingredients, and write a balanced chemical reaction with HCl.
______+ ______HCl ------> ______
______+ ______HCl ------> ______
7. Be sure to list at least two possible sources of error.
Household Acids and Bases
Introduction
Indicators often are used to determine the approximate pH of solutions. In this lab, you will make an indicator from red cabbage and use the indicator to determine the approximate pH values of various household liquids. The cabbage juice indicator contains a molecules, anthocyanin, that accounts for the color changes.