Question

1. List the proper GLP involve in the handling of a buret.

2. What is the tolerance of a 25mL & 50mL buret?

3. Briefly explain, what a Least Squares Analysis.

  

4. According to Fig. 3 in the Manual, what is the actual volume dispense, if 25mL were delivered.

Answer 1

1] burets are used for deliver liquids for volumetric titrations. it considered as a reference method. a standard 50ml buret is divided in to 1mL graduations with 0.1mL subdivisions. it must be leveling the eye with bottom of the meniscus.

for filling the burets;

• load 50 mL burets using a funnel.
• then it is rinsed inside with small volume of titrant including the the valve and tip.
• fill the buret and then run some in to waste beaker to check for air bubble in the tip.
• make sure all air bubble is cleared.
• then the solution level stabilize and record the initial volume to nearest 0.02 mL.

for titrating;  

• control the stop clock valve with your non dominant hand. this allows for finer control of valve and swirling of recieving flask with your dominant hand.
• in the case when you know approximate volume to be delivered you can add 80% quickly and then slow down near to end point.
• when the end pont is shown by a colour change you will observe a temporary change which disappears with swirling as you get close to the end point.
• to add less than a drop of titrant as end point approach, adjust the stopclock valve until titrant just begin to flow. close the valve and wash the hanging drop in to the recieving flask with a wash bottle.
• repeat the above procedure until the end point colour change is just clearly visible permanent more than 30 sec.

2]   

• tolerance of 25 mL buret; 0.03 mL
• tolerance of 50 mL buret; 0.05 mL

3] least squares method; it is a mathematical analysis used to determine the line of best fit for a set of data, by providing visual demonstration of the relationship between the data points. each point in the data represents the relationship between known independent variable and unknown dependent variable. in this method the set of data points plotted on x and y axis of graph. an analyst using the least squares will generate the best fit line from this. dependent variables are plotted on y-axis and independent variables are on the x-axis.

4] there are several devices used in the laboratory for dispensing measured volumes of liquid substances and solutions.

for example, you dispersed 25 mL of sample water then you are weighted water, and found that that 24.995 g at 25 degrees the density of water at 25 degree is 0.99707 g/mL .The true volume of water should be

volume=mass/density =24.995/0.99707=25.068 mL= 25.07 mL

The volume error is given by 0.07 mL