1.It is important to rinse all glassware before use in a chemical experiment. Wh

Question

1.It is important to rinse all glassware before use in a chemical experiment. When using a beaker to hold a solution that is to be pipetted, the beaker should be rinsed with

Select one:

a. distilled water..

b. the solution that it is to contain.

2.Before using a volumetric flask it should be rinsed with

Select one:

a. the solutiion that is to be diluted.

b. distilled water.

3.A pipette has a designated volume of 20.00 mL.A student uses the pipette to deliver three aliquots of water and determines the mass of each as follows:

20.0119 g

20.0009 g

20.0109 g

Calculate the relative spread of these masses and select the correct answer from the list below.

Select one:

a. 0.00055%

b. 0.011%

c. 0.055%

d. 20.0079%

4.There are 0.10 moles of actic acid in 100 mL of a particular solution. Which of the following is correct in expressing the concentration of acetic acid in this solutions as %w/v.

Select one:

a. 0.1 %

b. 0.6%

c. 0.01%

d. 6 %

5.What is the pI of an amino acid?

Select one:

a. The pH when the amino acid is in its zwitterionic form.

b. The pH when the acidic proton has been removed from the amino acid.

c. The pH when the amino acid first forms an ion.

d. The pH when the proton on the NH3 is removed.

Explanation / Answer

1) b, the glassware after rinsed with distilled water better rinsed also with the solution it is to be hold definitely.

2) a, volumetric flask to be rinsed with distilled water.

3) c, 0.055. T he difference between maximum value and minimum value = 0.011

so percentage of relative spread = 100*0.011/20   = 0.055

4)0.01 moles of acetic acid (AA) = 0.1* MW of AA = 0.1* 60 = 6 gr.

so 6 grams of AA is present in 100 ml of a solution ,

so its percent w/v = 6% w/v

5) a, pl is the isoelectric point. it is the pH at which any molecule will be neutral, carries no electric charge. Zwittr ion is a neutral molecule with having both +ve and -ve charges simultaneously. Zwitter ion of amino acid is a molecule containing NH3+ and COO- both positive and negative ions simultaneously.

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