Chemistry Module 10

1. Describe an acid

 

2. Descibe a base

1. It tastes sour and and turns blue litmus paper to red

 

2. It tastes bitter, slippery to touch and turns red litmus paper to blue

In the following equation, identify the acid and base

 

HCl + H2O -> H3O1+ + Cl1-

The acid is the HCl because it donates a H+.

 

The base is H2O because it accepts the H+.

What is the chemical definition of a base?

 

What is the chemical definition of an acid?

A base is any substance that accepts H+ ions.

 

An acid is any substance that donates H+ ions.

Which acid is diprotic

 

( diprotic means it donates 2 H+ ions)

 

A. HCl

 

B.H2PO4

C. H3O

 

 

 

B. H2PO4 is diprotic acid

What is an amphiprotic substance?

 

Give an example

Amphiprotic substances can act as acids or bases depending on the chemical formula it is in.

 

Water is a common amphiprotic

You have a brightly colored substance that you think could be an indicator for acids and bases. How could you make sure it is an indicator?
Mix the substance in known bases and acids and see if there is a color reaction for a base and a different color reaction for an acid. If it is an indicator, the color reaction for base will always be the same color for a base and the reaction for acid will always be the same color reaction for an acid.

What is wrong with the following statement:

 

“In a titration, the endpoint occurs when the number of moles of acid added equals the number of moles of base in the orignial solution, or vice versa.”

 

Hint: this exact question is on the test, study it!

The endpoint of a titration indicates that the number of moles of acid added are enough to eat up any base present. If the chemical equation indicates a 2:1 mole ratio, then the number of moles are not equal, they are a factor of 2 apart.
Write a balanced equation for the reaction between H3PO4 and NaOH.

This is an acid and ionic base, so we will follow the the acid+base —> salt+water formula. The salt comes from the metal ion of the base (Na+) and the negative ion left over when the acid donates an it H+ ions. The acid needs to donate three H+ ions, and when that is done, PO4-3 is left behind. To determine the formula, you switch the charges and drop the signs to make NA3PO4. Thus, the unbalanced equation is :

 

H3PO4 +NaOH –> Na3PO4 + H20

 

Now we balance it and the final is:

 

H3PO4 +3NaOH –> Na3PO4 + 3H20

 

 

What is the reacton between HI and Al(oH)3?

This is an acid and ionice base, so it will the the

acid + base –> salt + water formula.

the salt comes from the metal ion of the base (Al3+) and the negative ion left over whe the acid donates its H+ ions (I). To determine the formula, you switch the charges and drop the signs to make All3-. Thus, the unbalanced equation is

HI + Al(OH)3 –> All3 + H2O

 

The balanced equation is:

 

3HI + Al(OH)3 –> All3 + 3H2O

What reaction occurs between H2Cr2O7 and water?

Water is an amphiprotic compound; therfore, in the prescence of an acid, it will act as an base. This particular acid is diprotic, so it will donate 2 H+ ions to two water molecules and make two H3O+ ions. Once it does this, it will become Cr2O72, so the reaction is

 

H2Cr2O7 + H2O —> 2H2O + Cr2O72

Give the concentration in (M) of 1.11 moles of HCl are dissolved in enough water to make 1.5 liters of solution

Molarity is given by number of moles divided by number of liters. We have both those units, so we just divide them.

 

Concentration = #of moles  = 111 moles HNO3

                          #liters    = 1.5 L

 

equals: 0.74 M final answer

A chemist has a stock solution that is 6.78 M HCl. he wants to make 500 ml of 1.15 M HCl. What should he do?

This is a dilution problem, so we use the dilution equation. M1 is 6.78 M, we need todetermine V1. M2 is 1.15 M and V2 is 500 ml.

 

M1 V1 = M2 V2

 

(6.78M) * V1 = (1.15 M) * (500 ml)

 

V1 = 1.15 M * 500

    6.78 M

 

V1 = 84.8 ml

How many grams of sodium sulfate canbe produced if

500ml of 1.6 M sodium hydroxide is reacted with an excess of sodium sulfate?

In order to solve any stoichiometry problem, we must figure out the balanced chemical equation. According to the problem, our reactants are H2SO4 and NaOH. When they react, we learned that a salt and water will be produced. The salt will be composed of the positive ion from the base of (Na+) and the negative ion left over when the acid gets rid of allits H+ ions. In this case, that will be the SO42- ion. Thus, the reaction is:

 

H2SO4 + NaOH –> Na2SO4 + H2O

 

Now balance the equation and your final is:

 

H2SO4 + 2NaOH –> Na2SO4 + 2H2O

 

 

 

A chemist needs to determine the concentration of an unlabeled bottle of HBr. She titrates 15.0 ml of it with 1.14 M NaOH. It takes 45 ml of NaOH to reach the endpoint of the acid. Whatis the concentration of the acid?

Remember, titrations are just stoichiometry probelm, so first we have to come up with a balanced chemical equation:

 

HBr + NaOH –> NaBr + H2O

 

Since the endpoint was reached, we know that there was exactly enough base added to eat up all the acid. First, then, we calculate how many moles of base were added:

 

1.14 molesNaOH   x   0.0450L 

       1 L               x       1            = 0.0512 molesNaOH

 

 

We can now use the chemical equation to determine how many moles of acid were present:

 

0.0513 molesNaOH   x   1 mole HBr

             1               x  1 moleNaOH   =0.0513molesHBr

 

 

Now that we have th number of moles of acid present, we simply divide by the volume of acid to get concentration:

 

Concentration = #moles  = 0.0513 moles HBr 

                       # liters  =      0.0150 L            =

 

 Final Answer 3.42 M

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