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Chapter 4: Problem 36

An aqueous solution of an unknown solute is tested with litmus paper and found to be acidic. The solution is weakly conducting compared with a solution of \(\mathrm{NaCl}\) of the same concentration. Which of the following substances could the unknown be: \(\mathrm{KOH}\), $\mathrm{NH}_{3}, \mathrm{HNO}_{3}, \mathrm{KClO}_{2}, \mathrm{H}_{3} \mathrm{PO}_{3}, \mathrm{CH}_{3} \mathrm{COCH}_{3}$ (acetone)?

Short Answer

Expert verified
The unknown substance could be \(\mathrm{H}_{3} \mathrm{PO}_{3}\) (phosphorous acid), as it is acidic and a weak electrolyte.

Step by step solution

01

Eliminate non-acidic compounds

As we know that the solution is acidic, we can start by eliminating any substance that is not acidic or does not produce acidic solutions: 1. KOH: A strong base, not acidic. 2. NH3: A weak base, not acidic. So now, our list of possible substances is: HNO3, KClO2, H3PO3, or acetone (CH3COCH3).
02

Eliminate strong acids

Since the solution is weakly conducting, it indicates that the solute is a weak electrolyte. Thus, strong acids can't be the unknown substance: 1. HNO3: A strong acid (strong electrolyte), not a weakly conducting substance. Now, our list of possible substances is: KClO2, H3PO3, or acetone (CH3COCH3).
03

Investigate remaining substances

Finally, we will evaluate the remaining substances regarding their acidic nature and weakly-conducting property: 1. \(\mathrm{KClO}_{2}\) - When dissolved in water, it forms a neutral solution, so it can't be our unknown substance. 2. \(\mathrm{H}_{3} \mathrm{PO}_{3}\) - Phosphorous acid (H3PO3) is a weak acid (weak electrolyte), so it fits the criteria of being acidic and weakly conducting. 3. \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) - Acetone is a weakly-conducting organic compound that does not act as an acid when dissolved in water, so it can't be our unknown substance. So based on the given properties, the unknown substance could be: \(\mathrm{H}_{3} \mathrm{PO}_{3}\) (phosphorous acid).

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Most popular questions from this chapter

(a) Which will have the highest concentration of sodium ions: \(0.25 \mathrm{MNaCl}, 0.15 \mathrm{M} \mathrm{Na}_{2} \mathrm{CO}_{3},\) or \(0.075 \mathrm{MNa}_{3} \mathrm{PO}_{4} ?(\mathbf{b})\) Which will contain the greater number of moles of sodium ion: \(20.0 \mathrm{~mL}\) of \(0.15 \mathrm{M} \mathrm{NaHCO}_{3}\) or $15.0 \mathrm{~mL}\( of \)0.04 \mathrm{M} \mathrm{Na}_{2} \mathrm{~S} ?$

Pure acetic acid, known as glacial acetic acid, is a liquid with a density of \(1.049 \mathrm{~g} / \mathrm{mL}\) at \(25^{\circ} \mathrm{C}\). Calculate the molarity of a solution of acetic acid made by dissolving \(20.00 \mathrm{~mL}\) of glacial acetic acid at \(25^{\circ} \mathrm{C}\) in enough water to make \(250.0 \mathrm{~mL}\) of solution.

Citric acid, \(\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7}\), is a triprotic acid. It occurs naturally in citrus fruits like lemons and has applications in food flavouring and preservatives. A solution containing an unknown concentration of the acid is titrated with KOH. It requires $23.20 \mathrm{~mL}\( of \)0.500 \mathrm{M} \mathrm{KOH}$ solution to titrate all three acidic protons in \(100.00 \mathrm{~mL}\) of the citric acid solution. Write a balanced net ionic equation for the neutralization reaction, and calculate the molarity of the citric acid solution.

Bronze is a solid solution of \(\mathrm{Cu}(\mathrm{s})\) and \(\mathrm{Sn}(s) ;\) solutions of metals like this that are solids are called alloys. There is a range of compositions over which the solution is considered a bronze. Bronzes are stronger and harder than either copper or tin alone. (a) A \(100.0-\mathrm{g}\) sample of a certain bronze is \(90.0 \%\) copper by mass and \(10.0 \%\) tin. Which metal can be called the solvent, and which the solute? (b) Based on part (a), calculate the concentration of the solute metal in the alloy in units of molarity, assuming a density of $7.9 \mathrm{~g} / \mathrm{cm}^{3} .$ (c) Suggest a reaction that you could do to remove all the tin from this bronze to leave a pure copper sample. Justify your reasoning.

State whether each of the following statements is true or false. Justify your answer in each case. (a) When acetone, \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\), is dissolved in water, a conducting solution results. (b) When ammonium nitrate, \(\mathrm{NH}_{4} \mathrm{NO}_{3}\), dissolves in water, the solution is weakly conducting and basic in nature.
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