Question

The following primary standards can be used for the standardization of bases except.

	a.	Benzoic acid
	b.	Oxalic acid
	c.	CaCO3
	d.	KHP

A solution that may contain NaOH, Na ₂CO₃, and NaHCO₃, alone or in compatible combination was titrated with 0.1200 M HCl. The volume of the acid required to reach the phenolphthalein endpoint was 25.67 mL while 38.13 mL to reach the methyl red endpoint. What are the components of the mixture?

	a.	Na2CO3 only
	b.	NaOH only
	c.	NaOH and Na2CO3
	d.	NaHCO3 and Na2CO3

In the standardization of an acid solution with sodium carbonate, why is it necessary to boil the solution before completing the titration?

	a.	to destroy the buffering action of the resulting solution due to the presence of the carbonic acid and unreacted hydrogen carbonate
	b.	all of these
	c.	to eliminate the reaction product, carbon dioxide and carbonic acid
	d.	to achieve a sharper endpoint due to the large decrease in pH

1. What do you call a co-precipitated impurity in which the interfering ion occupies a lattice site in the precipitate?

   	a.	inclusion
   	b.	adsorption
   	c.	coagualation
   	d.	occlusion

1 points   

QUESTION 8

1. 1.      An ideal precipitating agent will yield a precipitate with the following properties except _____.

   	a.	Has very high solubility to avoid losses during filtration and washing
   	b.	Can be easily filtered and washed free of contaminants or impurities
   	c.	Inert towards components of the atmosphere
   	d.	Has known composition after appropriate heat treatment

A lab technician dissolved 2 mol of X in 1 liter of water in order to make a 2 M solution. What did they do wrong?

	a.	They used the wrong solvent.
	b.	They did not account for the increased volume of the 2 moles of X
	c.	They did not account for the decreased volume of the 2 moles of X.
	d.	They did not heat the solution to make it dissolve better.
	e.	They did not do the math right and it won't make a 2 M solution.

1. All of the following are favorable conditions for precipitation of metal cations EXCEPT   

   	a.	Precipitate at low pH
   	b.	Add dilute precipitating agent slowly with vigorous stirring
   	c.	Precipitate in dilute solutions
   	d.	Precipitate from hot solutions

1 points   

QUESTION 12

1. A buffer solution is one which _____.

   	a.	changes color upon addition of strong base.
   	b.	resists changes in pH upon addition of acid or base.
   	c.	contains the maximum amount of solute possible for a particular temperature.
   	d.	contains more than the expected amount of solute for a particular temperature and is       therefore unstable.
   	e.	contains an equal number of hydronium and hydroxide ions.

1 points   

QUESTION 13

1. Which combination of solutions is the best choice for making a buffer solution?

   	a.	equal volumes of 0.1 M formic acid and 0.1 M sodium formate
   	b.	equal volumes of 0.1 M sulfuric acid and 0.001 M sodium sulfate
   	c.	equal volumes of 0.05 M hydrochloric acid and 0.075 ammonium chloride
   	d.	equal volumes of 0.5 M nitric acid and 0.5 M sodium hydroxide
   	e.	equal volumes of 1 M acetic acid and 0.005 M sodium acetate

1 points   

QUESTION 14

1. Calculate the molarity of NaOH solution if 12.25 mL was used to titrate 0.2615 g of primary standard KHP (204.2 g/mole).

   	a.	0.2509
   	b.	0.1354
   	c.	0.1045
   	d.	0.1697

1 points   

QUESTION 15

1. For titration of weak acid with a strong base, which indicator can be used?

   	a.	bromocresol green
   	b.	methyl red
   	c.	phenolphthalein
   	d.	methyl orange

1 points   

QUESTION 16

1. Which of the following statements is FALSE?

   	a.	Absolute error is obtained by subtracting the true value from the measured value.
   	b.	Standard deviation is obtained by taking the square of the variance.
   	c.	Median is the middle value of a data set.
   	d.	Coefficient of variation is simply the relative standard deviation expressed as percentage.

1 points   

QUESTION 17

1. What is the concentration in % (m/v) of a NaCl solution prepared by dissolving 9.3 g of NaCl in sufficient water to give 350 mL of solution?

   	a.	37.6% (m/v)
   	b.	3.26% (m/v)
   	c.	0.455% (m/v)
   	d.	2.66% (m/v)

1 points   

QUESTION 18

1. In standardizing a solution of NaOH against 1.431 grams of KHP, the analyst uses 35.50 mL of the alkali and has to run back with 8.25 mL of acid ( 1 mL = 10.75 mg NaOH). What is the molarity of the NaOH solution?

   	a.	0.2118
   	b.	0.2598
   	c.	0.2044
   	d.	0.7831

1 points   

QUESTION 19

1. To calculate the Molarity of a solution when the solute is given in grams and the volume of the solution is given in milliliters, you must first:

   	a.	Convert volume of solution in milliliters to liters, but leave grams to moles
   	b.	None of the above
   	c.	Convert grams to moles, and convert volume of solution in milliliters to liters
   	d.	Convert grams to moles, but leave the volume of solution in milliliters

1 points   

QUESTION 20

1. The solubility of salt A in 100 mg of water is 25 grams at 25^oC. A solution is prepared by adding 30 milligrams of salt A in 100 grams of water at 25^oC. The resulting solution after mixing is a/an

   	a.	unsaturated
   	b.	supersaturated
   	c.	diluted
   	d.	saturated

1 points   

QUESTION 21

1. Precision refers to the closeness of measurements to each other. Which statistical parameter does not describe the precision of a set of data?

   	a.	coefficient of variation
   	b.	B and C
   	c.	absolute error
   	d.	standard deviation

1 points   

QUESTION 22

1. A sample consisting of Na ₂CO₃ and NaHCO₃, and inert matter weighs 1.179 grams. It is titrated with 0.100 N HCl with phenolphthalein as the indicator, and the solution became colorless after the addition of 24.00 mL. Another duplicate sample was titrated with HCl using methyl orange as indicator. It required 50.25 mL of the acid for the color change. What is the percentage of NaHCO₃ in the sample?

   	a.	21.58
   	b.	5.17
   	c.	11.60
   	d.	1.60

1 points   

QUESTION 23

1. Which statement correctly describes a weak diprotic acid titration?

   	a.	At the first equivalence point, the pH is calculated using the Henderson-Hasselbalch equation.
   	b.	At the equivalence point, there is maximum buffering capacity.
   	c.	The pH beyond the second equivalence point will rely on the amount of OH- remaining in solution.
   	d.	The initial pH will depend on the nature of the buffer composition.

1 points   

QUESTION 24

1. A solution contains 28% phosphoric acid by mass. This means that:

   	a.	1 L of this solution has a mass of 28 g
   	b.	1 mL of this solution contains 28 g of phosphoric acid
   	c.	100 mL of this solution contains 28 g of phosphoric acid
   	d.	1 L of this solution contains 28 mL of phosphoric acid

1 points   

QUESTION 25

1. A 300mg sample containing Na ₂CO₃, NaHCO₃, NaOH, and inert material either alone or in some combination was dissolved or titrated with 0.10 M HCl. The titration required 24.41 mL to reach the phenolphthalein endpoint and an additional 8.67 mL to reach the methyl red end point. Na₂CO₃ (105. 99), NaHCO₃ (84.01), NaOH (39.99). Identify the components of the sample.

   	a.	Na2CO3 and NaHCO3
   	b.	Na2CO3 only
   	c.	NaOH and NaHCO3
   	d.	Na2CO3 and NaOH

Answer 1

1. Oxalic acid can not be used as aprimary standard for acid-base titrations.

2. Phenolphtahlein acts as an indicator for complete reaction of NaOH and half reaction of Na2CO3 while methyl orange is an indicator for complete reaction of NaHCO3.. Thus, solution conains NaOH and Na2CO3.

3. It is necessary to boil the solution before completing the titration to destroy the buffering action of the resulting solution due to the presence of the carbonic acid and unreacted hydrogen carbonate.

4. Inculsion is known as the coprecipitated impurity in which the interfering ion occupies a lattice site in the precipitate.

12. A buffer solution is one which resists change in pH on addition of acid or base.

13. Buffer is a mixture of a weka acid and its conjugate base or a weak base and its conjugate acid. Also, any buffer is most effective when concenteartion of acid/base and its conjugate is almost equal. Thus, best buffer will be formic acid and sodium formate.

14. 1 mole KHP requires 1 mole NaOH to undergo neutralization reaction.

Moles of KHP = Wt of KHP / Molar Mass

= 0.00128 mol

Mol of NaOH = 0.00128 mol

Volume = 12.25 mL = 0.01225 L

Molarity = moles / Volume = 0.00128 mol / 0.01225 L = 0.1045M

15. Phenolphthalein is used as an indicator for weak acid-strong base titrations.