5pts anal chem

7/26/2019 5pts Anal Chem

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5pts

1. AGPART0031::Which of the following procedure is most likely to cause random error? Uncertainly

associated with a measuring device (e/g. buret).

2. The only cations is slightly acidic soln. are FE+++

, Zn++

and Cu++

. Which is reagent used in excess

would separate and identify the FE+++

in one step?

3. The presipitate obtained is Fe2O3. What is the gravimetric factor if the amount of Fe3O4needs to be

obtained? 2Fe3O4/3Fe2O3.

4. Two chemists submitted their respective analysis of lead found in samples of water from a polluted

river ( n = 30). A reference sample from their supervisor has a concentration of 12.0 ppb. Chemist 1

obtained an average of 11.6 ppb and a standard deviation of 1.8 ppb. chemist 2 obtained an average

of 11.0 and a standard deviation of 0.5 ppb. Compared to Chemist 1, Chemist 2 is less accurate but

more precise..


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5. Which of the following has no effect on the permanganimetric determination of calcium?Titration is

done at 70oC. as sabi ni gerik

6. A solution contains the following cations: Mn+2

, Bi+3

, Hg+2

, Ba+2

. The solution is saturated with H2S

soln. in NH4OH. The ion that will precipitate is Mn+2

.

7. If 50 ml of a sample of water required 6.4 ml of EDTA solution for titration and each ml of the

EDTA solution is equivalent to 0.40 mg Ca+2

, the ppm CaCO3hardness is: AT. WTS.: Ca = 40

CaCO3= 100 128.

Solution:

8. The most important requirement for a metallochromic indicator to be useful in signaling the

endpoint for a complexometric titration is that

The correct answer is: the condition formation constant between the indicator and the

metal should be smaller than the conditional formation constant between the titrant and

the samae metal ion..

9. Which type of contamination precipitates onto the surface of the colloid a normally soluble

compound? Surface adsorption.

10. Which combination of indicators is usually used for determination of combinations of any of these

soda ash components (NaOH, NaHCO3, Na2CO32)? Methly orange - phenolphthalein.

Solution:

11. The anions sulfate and sulfite have a common confirmatory test reagent. However, one can be

identified from the other because: BaSO4is insoluble in dil HCl while BaSO3is soluble.


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12. In standardizing HCl solution, it was found out that 50 ml of the solution was exactly equivalent to

1.325 g of Na2CO3(100% pure) using methyl orange indicator. What is the N of the HCl

solution? 0.50N.

13. A solution contains the following cations: Mn+2

, Bi+3

, Hg+2

, Ba+2

. The solution is saturated with H2S

soln. in NH4OH. The ion that will precipitate is Mn+2

.

14. A student standardized a solution of 0.05 N NaOH with 0.25g of KHP (MM = 204.20 and required 25.00

mL to reach the phenolphthalein endpoint. He obtained 4.897 x 10-5

N. His calculated normally is wrong

because. he should get 0.04897 N NaOH since the volume should be in liters..

Alternative:


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15. What is the percentage of Na2O in a sample of impure Na2CO3which weighs 1.1 g and which requires 35

ml of 0.5N H2SO4for titration to the methyl orange end point?0.4932.

16. Which combination of indicators is usually used for determination of combinations of any of these soda

ash components (NaOH, NaHCO3, Na2CO32)?Methly orange - phenolphthalein.

17. An unknown solution containing CO3=is clear and colorless. Which list of cations could it contain? K

+,

NH4+, Na

+.

Solution:

Since the solution is colorless,it contains K+, Na+, and NH4+. Cations of alkali (group 1A), alkaline

earth (group 2A) metals and ammonium ions are colorless since the electrons of these ions do not

absorb light in the visible region of the spectrum

18. What is the greatest advantage of doing potentiometric titration against all other titration methods? The

determination of the endpoint is not visual..

19. A 3.7818 g. sample of copper (50%) is discovered in HNOand diluted to 250 ml. If 25 ml of that solution

required 50ml. Of thiosulfate solution for titration of the liberated iodine, what is the copper titer of the

thiosulfate solution? 3.78 x 10-3

.

..

.


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20. Which of the following cations belong to the same group Cu+2

/ Cd+2

/ Hg+2

.

21. An analysis for disulfiram, C10H20N2S4, in Antabuse is carried out by oxidizing the sulfur to H2SO4and

titrating the H2SO4with NaOH. If a 0.4613-g sample of Antabuse is taken through this procdure, requiring34.85 mL of 0.02500 M NaOH to titrate the H2SO4, what is the %w/w disulfiram in the sample?7.00 %

w/w C10H20N2S4


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22. A sample of pyrite, FeS2, contains only inert impurities and weighs 0.5080 gms. After the sample has

been decomposed and dissolved, a precipitate of 1.561gm of BaSO4is obtained. If the calculated

percentage of S in the sample is 42.21% what weight of precipitated as Fe(OH)3and ignited as Fe2O3?

(MW of Fe2O3= 159.7; FeS2= 119.97; BaSO4= 233.40; S = 32.06; Fe = 55.85). 0.2670 g.

23. The titration reaction in permanganimetry is relatively slow but is catalyzed by the following except OH-.

24. In which of the following conditions is the solubility of AI(OH)3highest? A solution of NaF (AI3+

forms

AIF63-

with F-).

25. When performing EDTA titrations, pH is an important factor. Basic conditions are ensured since

most metals form complex with ions during this condition. Too basic conditions are avoided


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because. insoluble hydroxides and basic oxides form thus resulting to a negative error at the

endpoint..

26. A 1.5176 g sample of a CaCO3was dissolved in an acidic solution. The calcium was precipitated as

CaC2O4H2O (146.11) and the ignited precipitate at 230C was found to weigh 0.8249g. What is the

percentage of CaO (56.08) in the sample? 23.8%

27. A super phosphate fertilizer was analyzed for phosphorous. A 0.5414 gram sample produce 0.1277 g of

Mg2P2O7residue upon ignition of the magnesium ammonium phosphate precipitate. The percentage of

P2O5present sample is: 0.1504.

28. Approximately how many grams of NH4Cl (53.45) should be dissolved in a liter of 0.125 F NH3to

reduce the concentration of hydroxide ions to one-thousandth of its original value? 79g

29. A 1.500g sample of impure aluminum chloride was dissolved in water and treated with 45.32mL of

0.1000M AgNO3using K2CrO4as indicator. Express the analysis in %AlCl3(133.33). 13.43%


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30. A 750.25g alloy of nickel was dissolved and treated to remove the impurities. Its ammoniacal solution was

treated with 50 mL of 0.1075M KSCN and the excess cyanide required 2.25 mL of 0.00925M AgNO3.

Determine %Ni (58.69) in the alloy. 10.53%

31. As2O3is oxidized by KMnO4. The millequivalent weight of As2O3(MW = 197.84) as a reducting agent is:

0.04946.

Solution: milliequivalent Weight = (Formula weight/number of reacting units)(1 x 10-3

)

Milliequivalent wgt. = (197.84 g/mole / 4 eq./mole)(1 x 10-3) = 0.04946

32. A 7.279g sample of meat was analyzed for its nitrogen content using Kjeldahl method. Upon

digestion, the ammonia liberated was collected in 250mL of 0.855M H3BO3. The resulting solution

was titrated with 37.25 mL of 0.3122 M HCl using the mixed indicator. Determine the %protein in the

sample using 6.25 as factor for meat products. 13.98%

33. A mixture containing FeCl3(162.2) and AlCl3(133.33) only weighs 750.8 mg. The chlorides were

precipitated using ammonia and ignited to Fe2O3(159.69) and Al2O3(101.96), respectively. The oxide

mixture weighs 351.3 mg. The percentage of Al (26.98) in the sample is approximately 41%


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34.

Solution: NH4ClNH4++ Cl

-. Ammonium chloride is a polyprotic substance (can donate

hydronium ions) unlike the rest.

37.


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38.

Solution: Barium and Sodium does not have the same value of charge therefore,

they can be distinguished through flame test.

5pts anal chem

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