7.7: Unit 7 Practice Problems

$$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$

$$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$

$$\newcommand{\id}{\mathrm{id}}$$ $$\newcommand{\Span}{\mathrm{span}}$$

( \newcommand{\kernel}{\mathrm{null}\,}\) $$\newcommand{\range}{\mathrm{range}\,}$$

$$\newcommand{\RealPart}{\mathrm{Re}}$$ $$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$

$$\newcommand{\Argument}{\mathrm{Arg}}$$ $$\newcommand{\norm}[1]{\| #1 \|}$$

$$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$

$$\newcommand{\Span}{\mathrm{span}}$$

$$\newcommand{\id}{\mathrm{id}}$$

$$\newcommand{\Span}{\mathrm{span}}$$

$$\newcommand{\kernel}{\mathrm{null}\,}$$

$$\newcommand{\range}{\mathrm{range}\,}$$

$$\newcommand{\RealPart}{\mathrm{Re}}$$

$$\newcommand{\ImaginaryPart}{\mathrm{Im}}$$

$$\newcommand{\Argument}{\mathrm{Arg}}$$

$$\newcommand{\norm}[1]{\| #1 \|}$$

$$\newcommand{\inner}[2]{\langle #1, #2 \rangle}$$

$$\newcommand{\Span}{\mathrm{span}}$$ $$\newcommand{\AA}{\unicode[.8,0]{x212B}}$$

$$\newcommand{\vectorA}[1]{\vec{#1}} % arrow$$

$$\newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow$$

$$\newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$

$$\newcommand{\vectorC}[1]{\textbf{#1}}$$

$$\newcommand{\vectorD}[1]{\overrightarrow{#1}}$$

$$\newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}}$$

$$\newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}}$$

$$\newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} }$$

$$\newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}}$$

Question 1.

Given the molarity, find the normality of the acid or base.

0.24 M NaOH

1.2 M H3PO4

0.73 M H2SO4

0.24M x 1 = 0.24N

1.2M x 3 = 3.6N

0.73M x 2 = 1.5N

Given the normality, find the molarity of the acid or base.

1.5N HCl

0.84N Mg(OH)2

0.9N  NH4OH

1.5N / 1 = 1.5M

0.84N / 2 = 0.42M

0.9N / 1 = 0.9M

Question 2.

Given the H+ concentration, find the OH- concentration, and the pH.

[H+] = 0.0046 M

[H+] = 3.57 x 10-8 M

Remember the following formulas   [H+] x [OH-] = 10-14M              pH = -log [H+]

[H+] = 0.0046 M           OH- = 10-14/0.0046 = 2.2x10-12 M                 pH = -log(0.0046) = 2.3

[H+] = 3.57 x 10-8 M      OH- = 10-14/3.57x10-8 = 2.8 x 10-7 M           pH = -log(3.57x10-8 ) = 7.4

Question 3.

Given the pH, find the H+ concentration and the OH- concentration.

pH = 12.97

pH = 1.3

Remember the following formulas      [H+] = 10-pH              [H+] x [OH-] = 10-14M

pH 12.9            [H+] = 10-12.9 = 1.26 x 10-13M           [OH-] = 10-14/1.26x10-13 = 0.0794 M

pH 1.3              [H+] = 10-1.3 = 0.050 M                     [OH-] = 10-14/0.050 = 2.0 x 10-13M

Question 4.

Given the [OH-] concentration find the pH and state whether the concentration is acidic basic or neutral.

[OH-] = 4.6 x 10-2 M

[OH-] = 1.0 x 10-7 M

[OH-] = 5.2 x 10-9 M

Remember the following formulas   [H+] x [OH-] = 10-14M              pH = -log [H+]

[OH-] = 4.6 x 10-2 M     [H+] = 10-14/4.6x10-2 = 2.2 x 10-13           pH = -log(2.2 x 10-13) = 12.6             pH above 7 is basic

[OH-] = 1.0 x 10-7 M     [H+] = 10-14/1.0x10-7 = 1.0 x 10-7            pH = -log(1.0 x 10-7) = 7.0                pH of 7 is neutral

[OH-] = 5.2 x 10-9 M     [H+] = 10-14/5.2x10-9 = 1.9 x 10-6 M             pH = -log( 1.9 x 10-6) = 5.7              pH below 7 is acidic

Question 5.

Write the balanced chemical equation for the neutralization of phosphoric acid and magnesium hydroxide.  Then state whether the resulting solution will be slightly acidic, slightly basic, or neutral.

2H3PO4   +   3Mg(OH)2 →  Mg3(PO4)2 + 6H2O

weak acid + strong base = slightly basic

Question 6.

20.5mL of 0.25M sulfuric acid is used to titrate 34.0mL of sodium hydroxide.  What is the normality and molarity of sodium hydroxide?

NaVa = NbVb

Since the formula for sulfuric acid is H2SO4   Na = 0.25M x 2 = 0.50N

(0.50N)(20.5mL) = (Nb)(34.0mL)

Nb = 0.30N

Since the formula for sodium hydroxide is NaOH   Mb = 0.30N / 1 = 0.30M

Question 7.

Most toilet cleaners contain acid to help remove mineral deposits from the bowl.  If 38mL of toilet cleaner takes 26mL of 0.24N NaOH to titrate it, what is the normality of the toilet cleaner?